Biological Services Program
FWS/OBS-78/48
September 1978
Impacts of Transmission Lines
on Birds in Flight
Office of Research and Development
U. S. Environmental Protection Agency
Fish and Wildlife Service
U.S. Department of the Interior
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Fish and Wildlife Service to supply scientific information and meth-
odologies on key environmental issues which impact fish and wildlife
resources and their supporting ecosystem. The mission of the Program
is as follows:
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assessment.
2. To gather, analyze, and present information that will aid
decision makers in the identification and resolution of
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3. To provide better ecological information and evaluation for
Department of the Interior development programs, such as those
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Information developed by the Biological Services Program is in-
tended for use in the planning and decision making process to prevent or
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Biological Services Program
FWS/OBS-78/48
September 1978
IMPACTS OF TRANSMISSION LINES
ON BIRDS IN FLIGHT
Proceedings of a Workshop
Oak Ridge Associated Universities
Oak Ridge, Tennessee
31 January - 2 February 1978
edited by
Michael L. Avery
National Power Plant Team
1451 Green Road
Ann Arbor, Michigan 48105
Interagency Agreement no. 40-570-76
between U.S. Department of the Interior
and U.S. Department of Energy
Project Officer
Kenneth D. Hoover
National Power Plant Team
This study was conducted
as part of the Federal
Interagency Energy/Environment
Research and Development Program
Office of Research and Development
U.S. Environmental Protection Agency
Fish and Wildlife Service
U.S. Department of the Interior
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
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DISCLAIMER
The opinions, findings, conclusions, or recommendations expressed in
this report are those of the authors and do not necessarily reflect the views
of the Office of Biological Services, Fish and Wildlife Service, U.S. Depart-
ment of the Interior.
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PREFACE
Progress to alleviate the national and world energy problem will
come as individual issues are identified and acceptable solutions imple-
mented. One of the specific issues to emerge in the last few years in
the United States is the Impact of electric power transmission lines
on birds in flight. Therefore, the National Power Plant Team, Office of
Biological Services* U.S. Fish and Wildlife Service, requested Oak Ridge
Associated Universities {ORAU) to organize and convene a workshop of
knowledgeable experts to examine this issue and options for dealing with
it. The participants are listed at the end of this report.
Dr. Stanley Anderson ably served as Conference Chairman. He was
assisted by a Steering Committee consisting of Kenneth Hoover, Philip
Johnson* Roger Kroodsma, and Robert Wei ford. Prepared papers were
Invited and are included here as authored contributions. Five working
groups were organized, and we express appreciation to the following
individuals for their service as chairmen of these sessions:
Bird Behavior - Sidney Gauthreaux, Jr.
Habitat - James Tanner
Mitigation - Daniel Willard and Larry Thompson
Management Options - Spencer Amend
Research Priorities - Milton Friend
Their efforts in capturing the often spirited discussion and recording
both agreement and lack of agreement -- a difficult proposition at best
~ is appreciated. The editorial assistance of David Armbruster, ORAU,
and James Lewis, Office of Biological Services, is greatly appreciated.
Karen Kempf, Sally Vreeland, and Fran Scherger were instrumental in the
preparation of the manuscript.
All references cited in the individual papers are listed in a
separate section at the back of this Proceedings. Several additional
references pertinent to the subject of this Workshop, but not cited, are
also included at the suggestions of Nancy S. Dailey and Michael Avery.
These references are denoted by an asterisk (*).
Funds for support of this Workshop were provided by the Office of
Biological Services, U.S. Fish and Wildlife Service, and by the Environ-
mental Protection Agiency. Clearly, the ideas and suggestions expressed
in this report do not represent or imply any policy or position on
behalf of sponsoring agencies or participants' institutions.
Philip L. Johnson
Executive Director, ORAU
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TABLE OF CONTENTS
Page
INTRODUCTION - Kenneth Hoover 1
KEYNOTE ADDRESS: The Impact of Transmission Lines on
Birds (and Vice Versa) - Daniel E. Willard 3
Responses - Dale K. Fowler 8
Spencer Amend 10
INVITED PAPERS
Migratory Behavior and Flight Patterns -
Sidney A. Gauthreaux, Jr 12
Transmission Line Wire Strikes: Mitigation Through
Engineering Design and Habitat Modification -
Larry S. Thompson 27
Effects of Transmission Lines on Bird Flights: Studies of
Bonneville Power Administration Lines -
Jack M. Lee, Jr 53
Evaluation of a Proposed Transmission Line's Impacts on
Waterfowl and Eagles - Roger L. Kroodsma 69
Transmission Line Engineering and Its Relationship to
Migratory Birds - W. Allen Miller . 77
Routing Transmission Lines Through Water Bird Habitat in
California - Edward W. Col son and Ellen H. Yeoman 87
The Klamath Basin Case - Ira D. Luman 91
WORKING GROUP SUMMARIES
Behavior 105
Habitat 108
Mitigation 110
Management Options 118
Research Priorities 120
WORKSHOP SUMMARY - Stanley H. Anderson 127
Data Base on Avian Mortality on Man-Made Structures -
Nancy S. Dai ley 129
REFERENCES 131
PARTICIPANTS 147
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INTRODUCTION
Kenneth D. Hoover
U.S. Fish and Wildlife Service
The amount of land used for electric power generation and trans-
mission in the United States is expected to triple during the next 30
years. Current and future patterns of electric power transmission and
distribution lines across the country will increase the potential for
interference with the daily, seasonal, and migrational movements of
birds.
Habitats and flight pathways of birds are unavoidably altered by
the presence of overhead power lines and associated structures. Migration
and distribution patterns will also be affected if birds avoid areas
adjacent to these structures. The overall impact of transmission lines
on bird movements, however, is not fully understood, although it has
been the subject of an increasing amount of research in recent years.
While there are many documented cases of birds of prey, waterfowl, and
other large birds found dead or injured near transmission lines and
towers, the exact cause of death or injury has often been indeterminable.
Virtually no data are available on the impacts of transmission lines on
smaller birds.
Biologists and other decision makers are often called upon to
determine if proposed lines will, or existing lines do, cause bird
collisions, or whether nearby habitats may be affected by the presence
of such lines. Frequently they must rely on inadequate information to
address these problems or attempt to predict such impacts in a variety
of experimental ways.
Currently, proposed sites for transmission lines are evaluated on
the basis of several considerations. Among these are:
1. Proximity of these sites to certain types of habitat;
2. Probability of seasonal inclement weather;
3. Use of these areas by birds during the migratory, breeding,
and wintering seasons;
4. Use of these areas by individual species and the behavioral
characteristics of those species;
5. Design of proposed transmission lines and towers; and
6. Possible mitigation to reduce the impacts on birds in flight.
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The lack of a unified body of data from previous research and the
absence of a universal approach to study the problem have hindered its
resolution. The U.S. Fish and Wildlife Service and others have frequently
faced the question of impacts of transmission lines on birds, however,
no one individual or agency has been able to answer this question
adequately. Furthermore, much existing information is not specific to
transmission line impacts.
To review the current state of knowledge on this subject and to
draw together sources of information, the National Power Plant Team
(U.S. Fish and Wildlife Service) recently sponsored a "Workshop on the
Impacts of Transmission Lines on Birds in Flight". Three major questions
were addressed during this workshop:
1. What is the magnitude of the problem of birds striking trans-
mission lines and related structures?
2. What are possible short-term solutions to this problem?
3. What are the best approaches to use in the future to solve
this problem?
Resolution of these questions will enable those groups concerned
with transmission line impacts on birds, such as the U.S. Fish and
Wildlife Service and other federal conservation and regulatory agencies,
state fish and game commissions, electric utility companies, and conservation
organizations, to more accurately predict such impacts.
Pooling of information was facilitated by the presence of profes-
sionals from diverse technical backgrounds representing many of the
organizations mentioned above. A group discussion on each major issue
was followed by working sessions during which participants combined
their expertise to draw specific conclusions and develop recommendations.
Although participants represented groups with different interests and
goals, much valuable information on organizational structure, hierarchy,
and responsibility was exchanged and enhanced communication between
these organizations.
Finally, the workshop has stimulated the formulation of research
plans and coordination of research efforts resulting in studies utilizing
similar research techniques. Thus, the first step has been taken toward
creating a data base which will be useful in answering the three questions
the workshop addressed.
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THE IMPACT OF TRANSMISSION LINES ON BIRDS (AND VICE VERSA)
Daniel E. Willard
School of Public and Environmental Affairs
Indiana University
There is no controversy about whether birds collide with transmission
lines. Almost anyone who watches birds in the vicinity of lines has
seen a collision. Krapu (1974) has reported several well-documented
cases in North Dakota, and Anderson (1978) has done the same in Illinois.
The question turns on the importance or value of the fatalities.
Anderson (1978) and Kroodsma (1977) have questioned the importance of
the collisions in terms of the bird populations. Roy Hamilton (pers.
comm.) asks, further, how much is it worth to try to avoid collisions.
Transmission lines seem to have two kinds of effects on birds:
physical and electromagnetic. I will discuss only the physical in terms
of collisions. There is good evidence that birds are electrocuted by
towers and lines, but the number seems small. Some authors have reported
navigational disorientation and physiological damage resulting from
birds passing through electric fields. The evidence is inconclusive,
but, given the increasing number of ever higher voltage power lines, it
would appear that serious and careful study by unbiased (or several
equally, but oppositely, biased) groups is called for. The importance
of electrical effects needs discussion here.
Several authors have reported on the fatality rate due to collisions.
Stout and Cornwell (1976) summarized the causes of death reported in the
available literature. They estimated that 0.1 percent of the deaths
were caused by collisions. The largest category of collision was
transmission lines of one kind or another. Kroodsma (1977) reported
that less than 1 percent of the non-hunting waterfowl deaths in the
vicinity of the Red Wing, Minnesota power plant were power line related.
He, like others, points out the much higher mortality rate due to botulism
and, of course, hunting. Of the waterfowl populations he studied at a
power plant in Southern Illinois, Anderson (1978) reported 0.4 percent
mortality due to power lines. Over a period of a decade biologists at
the Patuxent Wildlife Research Center have analyzed all the dead Bald
Eagles they could get. In a series of articles authored by several
researchers, 6 to 8 percent of the Bald Eagle deaths were due to transmission
lines. At least twice as many were shot (Belisle et al. 1972, Coon et
al. 1970, Cromartie et al. 1975, Mulhern et al. 1970, Reichel 1969).
However, these sorts of calculations do not tell the whole story
for three reasons. First, fatalities and injuries are inadequately
reported. Second, a number of species may have higher death rates that,
because of their small populations, do not show in these data but,
because of their small numbers, nonetheless are important. Third, some
species are more biologically sensitive at specific places and seasons.
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Before continuing with these points in detail, I want to describe
two kinds of significance: biological and political. Biologists
generally think in terms of birth rates, death rates, population growth
rates, carrying capacity, and so on. A particular form of mortality
becomes important when it affects the ability of a species to survive or
maintain itself. We use bag limits to regulate the death rate of game
species to maintain healthy populations. For example, about one-third
of all Pintails are killed by hunters every year. In the Pacific Flyway,
that means hunters will kill between 1 and 1.5 million Pintails each
year. They will take home only about one-third of those because many
will die of lead poisoning and some cripples will not be recovered by
hunters. In any case, if about a thousand Pintails run into a trans-
mission line, it does not make much difference to the survival of the
species; the loss of a single California Condor or Whooping Crane may
have considerable biological significance.
Now, take those thousand dead Pintails and place them so that some
hunter or environmental group finds them and calls the governor, the
police, the national guard, or the media — that is political significance.
Change the Pintails to a species with an even wider constituency, such
as Canada Geese, and the political significance increases. Game species
have greater clout in some ways than rare and endangered species, even
though the biological threat to the latter is greater.
A few years ago I reviewed the literature on bird collisions with
various obstacles. Although much of the data was circumstantial, people
reported dead, usually maimed, birds under or near television towers,
bridges, transmission lines, fences, lighted buildings, unlighted
buildings, trolleys, the Cliffs of Dover, moving vans, airplanes, steam
shovels, fire towers, roller coasters (lighted and unlighted), smokestacks,
radio antennas, ships, grain elevators, and even a mounted horseman.
There are surely other obstacles. The amazing thing is not that there
are so many deaths or maimings but that there are so few reported losses.
The literature reports collisions for about 280 species representing
many families and orders. Swans, pelicans, cranes, and eagles are
reported in much greater numbers than their populations would suggest.
Either big, strikingly marked birds are easier to find and are more
noteworthy or they have more collisions per individual. In intensive
studies of television towers, it is obvious that passerines are frequent
victims.
At first, I thought that regular, intensive dead bird searches
under obstacles would reveal some reliable information about the risk to
bird populations from these obstacles. This reasoning is particularly
seductive for a linear net or fence like a transmission line. It seems
so simple to walk along under the lines looking for downed birds. Most
birds that strike a power line probably do not fall directly beneath it
and do not get counted, however. The majority fly off, and at some
distance from the line either recover or die. Although I have no evidence,
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I suspect the crippling and recovery rates vary with the nature of the
line, species, and behavior at the time. I have seen a number of such
bird collisions with lines and have never seen a bird come down, which
leads me to believe proportionally much greater numbers hit and run.
There is no way I know to estimate what happens to these birds.
Assuming there is a dead bird somewhere, probably no one looks for
it. While the literature tells us there is an agency which records the
falling of each sparrow, that agency has not seen fit to make its/his/her
data available to me. It is safe to say most nongame bird deaths are
unrecorded. Again, I cannot quantify further.
Suppose someone looks. What are the odds he will find a bird in
the area he searches? Anderson's paper (1978) is most revealing. Dogs
increase the likelihood of finding downed birds. Anderson also used
boats and an organized search team. However, when tested against
planted birds, his crew found only 58 percent of the birds. Depending
on terrain, and size and coloration of the birds, I suspect discovery
would vary considerably.
While the literature is replete with reports of dead birds under
lines, it is not always clear how the birds died. Unfortunately, in our
Oregon study (Willard and Willard in press), waterfowl chose to succumb
to lead poisoning, botulism, shot wounds, and other undetermined causes
under our study lines.
Our studies did not show, nor is there literature that indicates,
whether removal by scavengers is an important factor. In summary, it
appears that dead bird studies, even of game species, are inconclusive
enough to limit their usefulness as predictive tools.
I mentioned above that some species have such a small population
that the absolute number of deaths may be small but highly important to
the particular population. Sisson (1975) reported on the power line
induced deaths of 30 Mute Swans over 15 years. This population on the
Jordan River in Michigan has dropped from 70 to 25 since 1959. Two
birds per year could make a difference in such a small population. In
this species, not widely spread in North America, death becomes doubly
critical.
In the Klamath Valley of Oregon we found that 10,000 of the world's
40,000 Ross's geese passed through one of the alternative routes of a
proposed 500 kV transmission line (Willard et al. 1977). We were forced
to evaluate whether it was worse to threaten 10,000 Ross's Geese or,
alternatively, 3 million Pintails. Although we were able to avoid both,
the question remains - can we really compare the value of individuals of
one species with the value of individuals of another? Is this really a
biological question?
This experience suggests to me that we should take guidance from
the new strip mining legislation. This statute requires that Federal,
State, and local agencies list areas of such ecological significance
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that strip mining should be forever prohibited. We might set aside
buffer zones around areas of ecological importance to avian populations
so that all presumptively detrimental impacts would be forever prohibited.
One vehicle might be the Rare and Endangered Species Act. Obvious
suggestions are in the localities of the Aransas National Wildlife
Refuge (Whooping Cranes), Red Rock Lake (Trumpeter Swans), Lake Okeechobee
(Everglade Kites), and the Los Padres National Forest (California Con-
dors).
Some species are more in jeopardy during the breeding season when
their population can least afford it. About 200 pairs of White Pelicans
breed on the Lower Klamath Lake Wildlife Refuge. Raising a brood
requires both parents to forage extensively. The pelicans fly along the
canals about 30 feet high. While White Pelicans do not dive into the
water like Brown Pelicans, they do watch the water, locate prey, land,
and fish. As they watch the water while flying, they are distracted and
run into lines crossing the canals. During the 1976 breeding season
four adult female pelicans were found dead under wires. Autopsy showed
wires were the likely cause of death. Four out of 200 pairs were un-
successful in raising young. A 2 percent reduction is significant in a
small, otherwise threatened population. We see, then, that some species
have more significance than others and that certain times and places are
more important that others.
Where do we stand predictively? We know some things and we do not
know some others. Anderson (1978) lists at least five factors which
influence the frequency of waterfowl collisions with power lines:
number of birds present, visibility, species composition or behavior of
birds, disturbance, and familiarity of birds with the area.
We know how to count birds in the area. It may take time but it
can be done; in fact, in many cases it is being done. Our method in
Oregon will give us accurate data on where and how high birds will move
in an area. We know enough to predict changes in bird movements in
reponse to land use changes in our area.
We know less about visibility. Stout and Cornwell (1976), Krapu
(1974), P. Johnsgard (pers. comm.) and others agree that the worst cases
occur when visibility is reduced. Therefore, Kroodsma (1977) and others
have suggested marking wires in some manner. Sisson (1975) points out
that marking wires did not reduce the killing of Mute Swans. My own
studies are similar to Anderson's (1978) in that birds seem to be able
to avoid any wires they see, and most birds have good vision. They get
into trouble when they are preoccupied with landing, other members of
their own species, predators, or hunting. Waterfowl, particularly,
panic with the sudden appearance of an airborne predator. In short,
like humans, birds will run into things when they are not watching where
they are going.
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Species vary in ability to avoid lines. None seems immune. Swans
and pelicans seem particularly vulnerable, but this may be a result of
their detectability as corpses.
Disturbance seems important. We can calculate the probability of
a disturbance within broad limits; we cannot be sure when it will occur.
It appears that many kills occur when large numbers of birds are surprised
in conditions of poor visibility. In Oregon, waterfowl move about and
feed at night to avoid hunters. Because only a few fields are optimum
foraging areas at any one time, the birds gather in only a few special
fields and eat in huge, mixed flocks. Toward morning, fog forms.
Normally, birds will wait until visibility improves, but the hunters
come at legal dawn. Years of daily walking power lines paths might still
result in a researcher's missing this worst-case event when the independent
variables of farm practice, hunting pressure, fog, and disturbance
occur.
Bird familiarity with the area is hard to calculate. In Oregon, we
found migrating birds generally flew about 300 yards high, much too high
to interact with power lines. However, birds passed through the proposed
power line route at least twice daily on feeding flights. During hunting
season, they crossed the "firing line" well above shot range. On the
few windy and foggy days we experienced, the flocks flew about 20 yards
above the "firing line". I suspect bad weather would change their
normal behavior, even if they were familiar with the presence of power
lines.
All of this leads me to make some recommendations. Each point is
arguable depending on your relative values for power lines and birds.
1. Avoid ecologically sensitive areas.
2. Avoid vulnerable species.
3. Determine what it is worth to avoid sensitive areas and vulnerable
species.
4. Critically reexamine the value of devices increasing the
visibility of wires.
5. Control human access to waterfowl areas with existing lines.
6. Study the electromagnetic effects of power lines on birds.
7. Assume no correlation between conductor size and damage.
There is no evidence that 745 kV lines are a worse impact
threat than 69 kV lines. Perhaps the converse is true.
8. Control land use within one mile of new lines,
9. Accept dead bird studies with a certain degree of skepticism*
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RESPONSE TO KEYNOTE ADDRESS
Dale K. Fowler
Tennessee Valley Authority
Dr. Willard has done a masterful job of describing the state of the
art of this relatively new area of environmental concern. I know that
many of the thought provoking points he has made will be vigorously
debated over the next two days.
I am particularly intrigued by Dr. Willard's interpretation of
existing wire strike mortality data. If this information is relatively
meaningless, then we are not in a position to conclude that a serious
problem exists. We can speculate that more birds die from wire colli-
sions than are found, but we can also speculate, with some support from
existing data, that the number of dead birds in the vicinity of trans-
mission lines reflects a low incidence of fatal collisions. The magnitude
of the problem {or the lack of one) is a function of the number of dead
birds. Are these collision-related deaths frequent enough to justify the
added transmission line construction costs that some of Dr. Millard's
recommendations would require? Good mortality data are a prerequisite
to answering this question.
Dr. Willard's comments regarding species with dangerously low
populations are well taken. Any added source of mortality would be a
blow to such populations, and measures to reduce the likelihood of wire
strikes to these species should be weighed heavily against all the other
factors that are considered when siting and constructing new lines.
However, I would expect that potentially serious, collision-related
situations, such as proximity to threatened and endangered species
habitats, would be localized, highly site-specific, have a predictable
distribution, and include only small portions of a given power system. I
also suspect that the potential for such problems would vary among power
systems due to differences in land use, height of vegetation, topography,
climate, and other factors that would affect avian flight patterns.
Therefore, mortalities for one region, such as the West, may not be
representative of other regions, such as the Northeast or Southeast.
We know of very few documented bird collisions with Tennessee
Valley Authority (TVA) transmission lines. Occasionally we receive
reliable reports that large birds, such as Great Blue Herons, have been
found dead beneath our lines, so collisions do occur. However, these
reports are infrequent, and there has been no feedback from our biologists,
from biologists of other agencies, or from the general public to indicate
the existence of a serious problem.
Although we do not consider TVA transmission lines a significant
mortality factor to migratory bird populations, potential bird-wire
collisions are evaluated during the siting of new lines. Our TVA
biologists closely scrutinize corridors that pass near waterfowl
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refuges and other sensitive habitats, and their recommendations are
considered, along with many factors, in final route selection. Most
potential environmental problems can be identified and resolved during
transmission line siting. However, because there are many interest
groups to be considered in final route selection, the choice is seldom
easy.
We realize there might be specific sites within our power system
where factors could create a high probability of bird-wire collisions.
There are over 17,000 miles of transmission lines within the TVA system,
and obviously one cannot be absolutely sure about the likelihood of
site-specific problems being absent or present. However, it has been
our experience that where TVA-related environmental problems do occur,
there is little time lag between the occurrence of the problem and our
attention being drawn to it.
If we do have areas within the TVA power system that constitute
significant wire strike mortality problems, we want to know where they
are. Professionals in a diverse array of disciplines are employed by
TVA, and the agency is involved in many natural resource programs. Among
these is a very promising cooperative program, involving several other
agencies, aimed at establishing resident flocks of Giant Canada Geese in
the Tennessee Valley. Wire strike mortalities involving these geese, or
some of the other water and shorebirds we are working with, would riot be
welcome news to our waterfowl biologists.
We are conducting research to better understand the environmental
effects associated with TVA's right-of-way construction and maintenance
programs. We also have a cooperative, cost-sharing program available
for landowners who are interested in managing wildlife on TVA rights-of-
way on their land. Although these efforts do not directly pertain to
this workshop, they illustrate that where problems and opportunities related
to transmission lines have been clearly identified, TVA has been responsive.
We intend to do the same in the area of wire strikes if a serious problem
is quantitatively documented.
We do feel that this workshop will greatly clarify the present
confusion concerning avian mortalities associated with transmission
lines. Many utilities are understandably apprehensive about the economic
ramifications of this relatively recent environmental consideration. A
logical, objective evaluation of this situation is clearly needed.
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RESPONSE TO KEYNOTE ADDRESS
Spencer Amend
Kansas Forestry,
Fish, and Game Commission
Approximately one year ago (January 1977), Lawrence Livermore
Laboratory sponsored a gathering similar to this one in an attempt to
identify potential environmental hazards associated with geothermal
development. Shortly after that meeting Ken Hoover (U.S. Fish and Wild-
life Service) and I, as well as some others, discussed the possibility
of using this approach to identify and, in some orderly manner, to
establish priorities for efforts to obtain information we do not have
concerning the relationships between power lines and bird movement
patterns. So I feel some sense of satisfaction in the fact that we are
gathered for this purpose today.
When we were initially considering an appropriate composition for
this workshop, we agreed to be guided by the level of professional
expertise of those we would invite; that is, for the moment we are not
representing those who happen to be paying our salaries. A critical
factor in determining our final success will be the degree to which each
of us approaches this problem on a strictly professional and scientific
basi s.
Perhaps just a brief comment is in order concerning my perception
of the role of a reviewer in a situation such as this. I feel it is
appropriate for someone in this position to identify potentially con-
troversial areas in order that subsequent discussion can focus on and
clarify those areas.
I suggest that there is a very basic question which needs to be
addressed: "Oust why are we interested in birds anyway?" My answer is
based on that first wildlife text, to which Dr. Willard referred,
specifically the part about man's having dominion over the creatures of
the sea, land, and air. I suggest that indeed the purpose for our
interest in birds relates to our desire to enjoy and use them for our
own purposes, both consumptive and nonconsumptive. Indeed, the entire
science of wildlife management is predicated on the notion of manipulating
wildlife populations for man's enjoyment. This brings me to my first
point of issue with Dr. Willard. He states that the question turns on
the importance or the value of the fatalities involved. A more accurate
statement would encompass the importance relative to our abilities to
manage and subsequently to enjoy the birds involved. Apparently, both
Dr. Willard and Dale Fowler missed the principal point--at least from my
perspective—by focusing their attention solely on the collision aspect
and, more importantly, by overlooking the impact through habitat use or
behavioral changes on man's use of the bird resource.
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I concur with the approach of recognizing the important distinction
between biological and political significance in discussing power
line/ bird interactions. Biological significance, while no doubt an
overall issue of considerable importance, is, I think, not likely to be
demonstrable in relation to a single powerline, except in rare cases.
The cumulative effect of many lines in many locations within the areas
traversed by birds throughout their life cycles may be of greater significance
when considered with other mortality factors. The size of the species
population in question really serves only to increase the significance.
The next point I would like to deal with briefly is the scavenging
issue raised by Dr. Willard when he indicated there is no literature
indicating that removal by scavengers is an important factor. My own
recollection on this point is somewhat hazy, but some studies have
indicated that is is important (e.g., Goddard 1977, Scott et al. 1972).
Perhaps the computer bibliography can help clarify this point. As with
many issues, I suspect we will need to consider this one on a rather
site-specific geographical basis, and it is reasonable to expect considerable
variation.
Dr. Willard raised the question of whether we can really compare
the value of individuals of one species with the value of individuals of
another and implied that we would not wish to do so. I submit, however,
that this is quite a common and very realistic management question, one
which is often dealt with in setting priorities and determining how best
to direct our attention or to utilize our scarce resources.
I would like to endorse, for discussion purposes at least, the
suggestion that geographical areas be inventoried from the standpoint of
their sensitivities to adverse impacts of power lines. This kind of
inventory should be quite useful in not only allowing power line con-
struction to avoid highly sensitive areas but also helping resource
agencies focus data gathering efforts.
In considering Dan's nine recommendations, I feel a bit inadequate
in that no additional ones occur to me. I am particularly pleased with
the recommendation concerning land use within one mile of new lines,
although this does not appear to follow from the logic developed in the
paper. It arises generally and speaks to the point I made earlier about
habitat use and availability.
In conclusion, I believe Dan gave us a good keynote speech which
identifies several potential points of discussion, and I look forward to
attempting to resolve with you any conflicts I may have been able to
generate.
11
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MIGRATORY BEHAVIOR AND FLIGHT PATTERNS
Sidney A. Gauthreaux, Jr.
Clemson University
INTRODUCTION
Since the beginning of recorded history the migration of birds has
attracted the attention, and intrigued the imagination, of man. Bird
migration has likewise been of considerable interest to biologists, and
myriad studies have sought answers to the hows and whys of bird migration.
Many of these studies have been summarized in books devoted entirely to
the subject {e.g., Brewster 1886, Clarke 1912, Coward 1912, Cooke 1915,
Thomson 1926, Wetmore 1926, Tinbergen 1949, Rudebeck 1950, Lincoln 1952,
Dorst 1962, Schuz 1971, Bykhovskii 1974, Griffin 1974). The amount of
data that has been collected and the published findings on all aspects
of bird migration is truly staggering, and even the most comprehensive
reviews have been able to provide little more than a sketchy overview of
the subject.
In this paper I will review some facts about bird migration with an
emphasis on the geographical distribution of migrants; the seasonal and
daily timing of migration; the direction, route, and altitude of migratory
flights; and the influence of weather on the density of migration. This
information will permit a better appreciation of the potential impact of
transmission lines on all kinds of migratory birds. Although we cannot
say what this impact is because of the lack of carefully designed,
quantitative studies, reports of bird fatalities at TV towers, tall
buildings, and the like during migration suggest that on certain occasions
the impact could be considerable.
GEOGRAPHICAL DISTRIBUTION OF MIGRANTS
A wealth of information on the distribution of North American
migrant birds can be gleaned from the pages of American Birds (formerly
Audubon Field Notes) and the range maps of Robbins et al. (1966).
Additional information on the geographical pattern of the breeding
density of certain migrant species can be obtained from the "Breeding
Bird Survey of the United States Fish and Wildlife Service". MacArthur
(1959) analyzed the breeding distribution of North American passerines
wintering primarily in the neotropics (Figure 1). He found that the
eastern deciduous forests contained far more neotropical migrants than
northern coniferous forests and grasslands, and he correlated these
differences with the contrast between winter and summer food supplies in
the given habitat. Will son (1976) in a partial reanalysis of MacArthur's
(1959) findings showed that:
1. North American neotropical migrants are less prevalent in
grasslands than in forests, but there is no significant
difference in the proportion of neotropical migrants in
deciduous and coniferous forests.
12
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Figure 1. The distribution of the percentages of bird species breeding
in the United States but overwintering in the neotropics.
Note that the eastern third of the country contains the greatest
percentages of neotropical migrants (after MacArthur 1959).
2. Coniferous forests have relatively fewer year-round resident
individuals than grasslands or deciduous forests, and grasslands
and coniferous forests have slightly fewer resident species
than deciduous forests.
3. Most neotropical migrant birds breed primarily in deciduous
forests, and most of those that breed in coniferous forests
are parulids (i.e., American warblers).
In the northeastern deciduous forests, on the average, 62 percent
of the breeding species and 75 percent of the individuals are migrants.
In the northern coniferous forests, 80 percent of the breeding species
and 94 percent of the individuals are migrants, while in the grasslands
76 percent of the breeding species and 73 percent of the individuals are
migrants. Although similar analyses for waterfowl and shorebirds are
not available, distribution and migration data can be found in Bell rose
13
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(1976) and Palmer (1976) for waterfowl and in Stout et at. (1967) and
Sanderson (1977) for shorebirds.
In general there is considerably more bird migration in the eastern
two-thirds of the United States than in the West (Lowery 1951; Lowery
and Newman 1955, 1966). One basis for this pattern is that more migrants
(species and individuals) breed in the East, but another basis is exemplified
in Figure 2. The breeding range of the Philadelphia Vireo extends
toward the northwest into Canada, but its migration is restricted to the
eastern United States. Approximately 33 species of land bird migrants
conform to this pattern. Thus, even though a number of land bird migrants
breed considerably farther west and north of the eastern forests of the
United States, they migrate through the eastern States. The White-
throated Sparrow is an example of a short-distance migrant that winters
in the southern portions of the United States (Figure 3). Even though
the breeding and wintering ranges extend westward, the spring and fall
migration of the species is almost exclusively east of the Rocky Mountains.
SEASONAL TIMING
Much of what we know about the seasonal timing of bird migration in
North America comes from the work of field observers and birdbanders,
and their findings have been regularly summarized in the spring and fall
migration issues of American Birds. Virtually every State has a check-
list or bird book containing information on the seasonal occurrences of
migrant birds. Saunders (1959) examined the variation in the timing of
spring arrivals among 50 different species in comparison with the mean
40-year arrival dates and found that in late, cold springs migrants
arrived later than in early, warm springs. Gauthreaux and LeGrand
(1975) associated the advancement or retardation of the seasonal timing
of migration with year-to-year changes in continental wind patterns.
Robbins et al, (1966) has summarized considerable data on the seasonal
timing of bird migration for most North American species. This information
is presented on species maps as isochronal lines that show the average
first-arrival date where birds migrating to the north may be seen about
the first of March, April, May, and June. Preston (1966) has analyzed
mathematically the timing of spring and fall migration and found that in
general those species that leave early return late (e.g., waterfowl,
sparrows). Preston discusses evidence that shows breeding birds occupy
their summer habitat as soon as it is habitable and depart as soon as
they have finished breeding. The standard deviation of the timing of a
species' migration is less in spring than in fall, hence the birds are
better synchronized in spring. During fall migration some species show
an almost bimodal timing with young and adults traveling at somewhat
different times (Murray 1966). In the spring, males of most species
arrive before the females, and adults precede young (Gauthreaux 1978a).
A number of factors must be considered in discussing the seasonal
timing of migration. The more important of these are vegetational
development in the spring, food availability, and climatic factors in
spring and fall. Weydemeyer (1973), in a 48-year study of spring arrivals
of migrants in Montana, found that ranges in dates of arrival were
14
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Figure 2. The breeding distribution and migration area of the Philadelphia
Vireo (Vireo philadelphicus). Although the breeding range of
this species extends into northwestern Canada, its migration
through the United States is confined to the eastern half of
the country (after Robbins et al. 1966).
15
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Figure 3. The breeding and wintering distribution of the White-throated
Sparrow (Zonotrichia albicollis) in North America. Although
the breeding range and wintering range of this species extend
beyond 120°W, the species migrates almost exclusively to the
east of the Rocky Mountains (after Robbins et al. 1966).
16
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greatest during late March and April and least in late May and June.
Slagsvold (1976) working in Norway founcf that for the country as a whole
there was a 6-day delay in bird arrival for each 10-day delay in vegetation
development. Thus, the arrival of migrants at higher latitudes and
altitudes was faster than the development of vegetation. Slagsvold also
found that earlier arriving species varied considerably in arrival date
at a particular locality from year to year, but late arriving species
had much less variation in arrival time. Minkowski and Bajorek (1976)
examined the spring arrival dates of 29 common or conspicuous migrants
and summer resident species in southern Michigan over a 7-year period.
They concluded that granivorous, omnivorous, and aquatic species tend to
arrive earlier than strictly insectivorous species, and that earlier
arriving species have a greater variance in arrival time than the later
arriving species.
DAILY TIMING OF MIGRATION
The majority of small birds, including most passerines, migrate at
night, and most waterfowl and shorebirds migrate both at night and during
the day. Raptors, several woodpeckers, swallows, several corvids,
bluebirds, and blackbirds migrant during daylight hours. The determination
of whether a species migrates at night or during the day has come from
laboratory studies of Zugunruhe--miqratory restlessness in caged birds
(Gwinner 1975); from data gathered when migrating birds collide with TV
towers, buildings, or power lines or when migrants are attracted to and
killed at, lighthouses and ceilometers (see Weir 1976 for review); and
from direct visual studies of daytime migration in progress. According
to data gathered by surveillance radars at several localities in the
United States and Canada, considerably more birds migrate at night than
during the day (Gauthreaux 1975).
A number of studies have shown the temporal pattern of nocturnal
migration (e.g., Lowery 1951, Sutter 1957a, Harper 1958, Gauthreaux
1971). As can be.seen in Figure 4, the initiation of nocturnal migration
occurs about 30 to 45 minutes after sunset; the number of migrants aloft
increases rapidly, peaking between 2200 and 2300. Thereafter, the
number of migrants aloft decreases steadily until dawn, indicating that
migrants are landing at night. Daytime migration is initiated near dawn
(sometimes earlier), peaks around 1000, and declines to minimal density
shortly after noon (Sutter 1957b, Gehring 1963, Gauthreaux 1978b).
DIRECTIONS AND ROUTES OF BIRD MIGRATION
Although considerable attention has been directed to laboratory
studies of direction finding in migratory birds (Emlen 1975), there is
an increasing emphasis on field studies of migratory orientation using
direct visual means (Lowery 1951, Lowery and Newman 1963, Gauthreaux
1969) and radar (Eastwood 1967, Gauthreaux 1975). Radar can provide
detailed information on the direction of migratory movements when
conditions for direct visual studies are poor while at the same time
sample a fairly large geographical area. Figure 5 is a photograph of
the display of the ASR-4 radar operated by the Federal Aviation Admin-
17
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Figure 4. The average hour-to-hour variation in the quantity of nocturnal
migration plotted as the percentage of peak density. The data
for eight nights were gathered using WSR-57 weather radar
during the spring of 1965 in southwestern Louisiana (see
Gauthreaux 1971 for more details).
Figure 5. A photograph of the ASR-4 radar screen showing echoes from
birds migrating toward the NNE. The range marks are located
every 2 nautical miles. Echoes from aircraft appear near 6 nm
range at 80° and 10° azimuths. The photograph was made on 27
April 1972 at Greenville, South Carolina (Federal Aviation
Administration ASR-4 radar installation), at 1947 EST.
18
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istration at the Greenville-Spartanburg Airport in northwestern South
Carolina. Similar radar systems are operated at many medium-sized arid
large airports throughout the United States. Echoes from individual
birds can be seen moving toward the north-northeast. Movement is indicated
by the "tails" of echoes produced by the fading of previously registered
echoes.
Radar studies of bird migration have been conducted in Illinois
(Graber and Hassler 1962, Bellrose and Graber 1963, Hassler et al. 1963,
Bellrose 1964, Graber 1968), coastal New England (Drury and Keith 1962,
Nisbet 1963a, Drury and Nisbet 1964, Nisbet and Drury 1968), eastern New
Jersey {Swinebroad 1964), coastal Virginia (Williams et al. 1972, 1977),
South Carolina (Gauthreaux 1974, 1976, 1978b), northern Georgia (Gauthreaux
and Able 1970; Able 1973, 1974; Gauthreaux in prep.), coastal Louisiana
(Gauthreaux 1971, 1972; Able 1972, 1973, 1974; Fuller 1977), northern
Ohio (Tolle and Gauthreaux in prep.), Arizona, New Mexico, and western
Texas (Beason 1978), several locations in Canada (Richardson 1969, 1971,
1972; Blokpoel and Defosses 1970: Myres and Cannings 1971; Richardson
and Gunn 1971; Speirs et al. 1971; Blokpoel 1974; Blokpoel and Gauthier
1974), and in northwestern Alaska (Flock 1972, 1973; Hubbard and Flock
1974). Although there are many geographical gaps in the coverage and
some studies have concentrated on waterfowl migration (e.g., Bellrose
1964, Blokpoel et al. 1975), particularly west of the Rocky Mountains
(Beason 1978), a continental pattern of bird migration in North America
is beginning to emerge.
In general, the axis of migration for most passerines is northeast
to southeast in the eastern two-thirds of the United States, but in
central southern Canada the axis of passerine migration is northwest to
southeast. Bellrose (1964, 1976) has shown that most waterfowl in
the Mississippi valley move more north-south with eastward and westward
deviations depending on topographic factors (Takes, marshlands, and
river systems). Wind direction exerts a strong influence on the direction
and timing of migration (Gauthreaux and Able 1970, Able 1974, Alerstam
1976), and the routes birds fly appear to be determined, at least in
part, by the prevailing wind patterns in North America during spring and
fall (Gauthreaux 1972). For example, in northwestern South Carolina in
spring the prevailing winds blow to the northeast, and the average
distribution of the directions of nocturnal migration on calm nights
(that is, when wind directions are not an influencing factor) in spring
is toward the northeast (29.5°). Thus, in spring the preferred direction
of migrants closely matches the prevailing wind direction. In fall the
winds in the same area usually blow toward the southeast, and the average
distribution of the directions of nocturnal migration on calm nights is
toward the southwest (231.5°). These data were gathered using direct
visual means, moon-watching (Lowery 1951), and ceilometer-watching
(Gauthreaux 1969), but data gathered from radar conform to the above
pattern (see Gauthreaux 1978b for details). Wind direction in relation
to the normal direction of migration can also influence the altitude of
migration as well as the number of migrants aloft, and these topics are
discussed below.
19
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There have been very few field studies of the influence of power
lines or other electromagnetic devices on bird migration, but there is
some evidence that when local magnetic fields are disrupted by electrical
currents, the orientation of birds is affected slightly (see discussions
by Southern 1975, Larkin and Sutherland 1977, Moore 1977). The magnetic
disturbance produced by electric current in power lines is generally
localized and does not extend beyond a distance of several meters.
Thus, the effects on the orientation of migrating birds may be minimal
when birds fly well above the power lines, but clearly more work is
needed on this subject.
ALTITUDE OF MIGRATION
Radar has provided the best data on the altitude of bird migration,
and radar studies have shown that most bird migration normally occurs at
altitude below 500 m above ground level (Nisbet 1963b; Eastwood and
Rider 1965; Able 1970; Bellrose 1971; Blokpoel 1971a, 1971b; Bruderer
and Steidinger 1972; Gauthreaux 1972). In general, the larger the bird
species and the faster its airspeed, the higher it flies during migration
for minimum cost of transport (Tucker 1975).
The distribution of nocturnal migrants in the airspace is strongly
skewed to the lower altitudes. In Table 1 the quantity of nocturnal
migration per altitudinal stratum is expressed as the percentage of the
total number of birds aloft. The data were gathered using WSR-57 weather
radar at New Orleans, Louisiana, in the spring of 1967 (see Gauthreaux
1970, 1972). Seventy percent of the migrants at night were most frequently
between 241 m (800 feet) and 1127 m (3718 feet), and within this zone
approximately 75 percent were between 241 m (800 feet) and 482 m (1600
feet). In Table 2 the altitudes of peak densities of migrants aloft on
Table 1. Altitude of nocturnal migration at New Orleans (expressed as
a percentage of total number of birds aloft).
Antenna elevation Altitudinal zones in meters
2.5°
241-1127
482-1690
724-2254
965-2817
(N « 34)
X
70
20
8
4
S.D.
19
13
10
8
N * 30)
241-482
482-724
724-965
965-1206
X
74
18
7
2
S.D.
17
14
B
3
20
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70 spring nights arid 35 fall nights are given. These measurements were
made with the VISR-57 radar at weather stations in New Orleans and Lake
Charles, Louisiana; Athens, Georgia; and Charleston, South Carolina.
Seventy-three percent of the 79 altitude measurements on 70 spring
nights showed the altitudes of peak densities of migrants to be at 305 m
or lower. In the fall, 56 percent of the 39 measurements on 35 nights
indicated that the greatest concentrations of migrants aloft were at 305
m. As Table 2 shows, on some occasions the altitude at which most birds
were migrating was considerably higher than the usual 305 m.
Most radar cannot detect birds very close to the ground (but some
shipboard navigation radar can), and consequently the minimum altitude
of nocturnal migration displayed on radar cannot be measured accurately.
Studies using direct visual means to detect migrating birds as they pass
through a narrow vertical beam of light (Gauthreaux 1969) suggest that
a considerable number of birds fly within 100 m of the ground at night.
This is particularly so within an hour after the initiation of nocturnal
migration and at the time birds are landing during the night. On some
misty, cloudy nights tremendous numbers of call notes from migrants
Table 2. Altitude of greatest concentration of nocturnal migrants aloft.
Altitude Number of observations
Meters Feet Spring Fill
152
500
1
—
305
1000
57
22
457
1500
3
2
610
2000
6
3
762
2500
2
1
914
3000
—
1
1219
4000
2
1
1372
4500
3
-
1524
5000
1
3
1676
5500
1
2
1829
6000
2
2
2134
7000
1
1
22S6
7500
—
1
Total 79 39
21
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aloft can be heard, and on many of these occasions the distance of the
call notes overhead indicates the birds are flying within a few meters
of the ground. The altitude of migration changes throughout the night.
Usually the maximum mean altitude of migration is reached about 2 hours
after initiation, and thereafter slowly declines as birds begin to
terminate their nightly migration (Able 1970).
Daytime migration usually occurs at altitudes below 300 m, and
quite often flocks of daytime migrants can be seen moving just above
tree level. This, however, is not always the case. When migrants are
arriving on the northern coast of the Gulf of Mexico during daylight
hours in spring after a trans-Gulf flight, they are usually at altitudes
above 1500 m (Gauthreaux 1971, 1972). When the migrants encounter a
cold front and headwinds before they make their landfall, they will
often fly within a few meters of the water's surface. On those occasions
when the flights are delayed and most of the migrants arrive at night,
tremendous numbers will strike wires, towers, and the like. In general,
daytime migrants will fly lower when there is poor visibility, dense
cloud cover, and drizzle.
WEATHER INFLUENCES ON THE DENSITY OF MIGRATION
Figure 6 shows the radar displays of nocturnal migration on ASR-4
radar with different migration traffic rates (Gauthreaux 1978b). These
displays were quantified by direct visual means (moon-watching [Lowery
1951] and ceilometer observations [Gauthreaux 1969, Able and Gauthreaux
1975]). After being calibrated, the radar can be used to measure the
quantity of migration, and it is possible to study the weather factors
responsible for the night-to-night variation in the quantity of migration.
It is generally accepted that in spring more migration occurs on the
west side of a high pressure system and before a cold front and low
pressure system (zones 4 and 5 in Figure 7). In fall very large migrations
occur just after a cold front on the east side of a high pressure system
(zones 1 and 2 in Figure 7). But what weather factors or combination of
weather factors influence the density of migration?
In the last several years a number of studies have attempted to
answer this question (see Richardson 1978 for a detailed review of this
subject). Because weather factors interact in complex ways, multivariate
statistical analyses must be used, and the results of studies using such
analyses have been summarized in Tables 3 and 4. Table 3 gives the
weather factors that have been shown to significantly influence the
quantity of spring migration. Of all the weather factors listed, wind
and temperature are clearly the most consistently important factors. In
fall (Table 4) the same pattern is found. Both wind and temperature
are, of course, significantly intercorrelated. Thus, the largest spring
migrations occur with winds from the south and southwest, which bring
warming temperatures, and the largest fall migrations occur with winds
from the northwest and north, which usually bring colder temperatures to
an area. Another point regarding the influence of weather on the quantity
of bird migration should be mentioned. The amount of night-to-night
22
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Figure 6. Photographs of the ASR-4 radar screen showing the changes in
the density of bird echoes as a function of migration traffic
rate (the number of birds crossing 1 mile of front per hour).
All photographs were made with the radar adjusted to 6 nm
range, the same high gain setting, Moving Target Indicator
(MTI) engaged, and no attenuation circuits engaged. As can be
seen, after the traffic rate (TR) is about 30,000 birds, the
screen is essentially saturated with bird echoes. (A) 9 May
1977, TR = 2000; (b) 12 May 1977, TR = 5000; (C) 24 April
1977, TR = 10,400; (D) 21 April 1977, TR = 12,000; (E) 28
April 1977, TR = 21,600; (F) 11 May 1977, TR = 32,400; (G) 26
September 1977, TR = 52,000; (H) 28 September 1977, TR =
218,700.
23
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Figure 7. A generalized synoptic weather pattern showing zones used in
analyzing the relationship between synoptic weather and the
density of bird migration in spring and fall. The arrows
indicate the general pattern of airflow.
variation in the quantity of migration explained by weather is 50 to 60
percent on the average. The remaining variation is undoubtedly due to
the internal conditions of the migrants (e.g., energy for migration,
physiological readiness to migrate) and the actual number of ground
migrants in an area.
The weather conditions most often associated with migrants colliding
with man-made objects (poor visibility, low ceiling, drizzle) are not
those conducive to very large migratory movements. Why, then, do tremendous
numbers of migrants collide with TV tower guy lines, buildings, and
other obstructions during migration? The answer to this question is
rather straightforward. When birds initiate a migration with favorable
24
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Table 3. Influence of weather variables on spring migration
(multivariate analyses).
General v
*
0.26
Bruderer (1978)
*
*
0.52
aSpec1f1c weather variables (e.g., 24-hour change in temperature, temperature departure from
normal) are Included in general variable (e.g., temperature.)
b
September,
cOctober-November.
dNovember.
25
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weather conditions, they sometimes move into areas where the weather has
deteriorated (e.g., a stalled frontal system), and this combination of
events is usually associated with such disasters. Occasionally disasters
occur under ideal weather conditions for migration, but these are exceptional
(Avery et al. 1977).
ACKNOWLEDGEMENTS
I wish to acknowledge the personnel of the United States Weather
Bureau and the Federal Aviation Administration for their generous cooperation
in permitting me to use their radar systems during my bird migration
work. I also wish to acknowledge the continued grant support of the Air
Force Office of Scientific Research for my ongoing research program in
bird migration. The manuscript was brought into final form while I held
grant AFOSR 75-2782, and I thank Anne Snider and Frank Moore for their
assistance in the preparation of the manuscript.
26
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TRANSMISSION LIKE WIRE STRIKES:
MITIGATION THROUGH ENGINEERING DESIGN AND HABITAT MODIFICATION
Larry S. Thompson
Montana Department of Natural Resources and Conservation
INTRODUCTION
Collisions of birds with overhead utility wires are nothing new.
Over a century ago, Coues (1876) documented bird kills resulting from
collisions with overhead telegraph lines, and wire strikes have probably
been a continuing source of avian mortality ever since. Wire strikes
have not received a great deal of public or scientific attention, how-
ever, until the last few years. As more and more overhead utility lines
are built, heavy bird losses are reported with increasing frequency, and
public concern over future losses becomes great. Unfortunately, much of
the existing problem stems from the fact that nearly all utility lines
operating today were built without knowledge of the causes, magnitude,
or importance of wire strikes - and, hence, without considering wire
strikes in siting or line design. Thus, we are suddenly realizing that
the thousands of miles of overhead wires strung across the continent --
many crossing wildlife refuges and other areas heavily used by migratory
birds -- may pose a very real threat to bird populations, and we must
try to do something about it. Also, the probability of wire strikes is
acknowledged to be an important consideration in environmentally sound
design and siting of new lines. We are therefore faced with the dual
problem of doctoring existing lines in an effort to correct past mistakes
and of ensuring that new lines will result in the least possible collision
mortality.
In this paper, I will summarize factors influencing the probability
of wire strikes and discuss means whereby such losses can be mitigated
or prevented. While the small body of literature developing on wire
strikes provides invaluable information relevant to the mitigation of
wire strike mortality, most of the material presented here is based upon
unpublished data and on conversations with many knowledgable individuals.
I will also discuss the significance of wire strikes and the relative
cost effectiveness of efforts toward mitigation.
FACTORS INFLUENCING THE PROBABILITY OF WIRE STRIKES
Predictability, or the a priori estimation of the probability of
wire strikes under certain conditions, is a requisite to mitigation.
However, there is a dearth of quantitative information on specific
circumstances or rates of collision mortality, information which is
essential to predicting high risk situations.
27
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In certain circumstances, overhead wires may cause a small but
regular loss of birds, which can be measured over time to estimate rate
of kill. This has been attempted by Willard et al. (1977) who derived
estimates of rates of wire strikes in the Klamath Basin of Oregon
ranging from 0.4 to 162 birds/mile/year. Anderson {1978) estimated that
from 0.2 to 0.4 percent of the maximum number of waterfowl present were
killed by twin 345 kV transmission lines crossing a slag pit in Illinois.
By observing diurnal waterfowl flights in this area, Anderson found that
0.01 percent of the total flights observed in the vicinity of the lines
(only 4 percent of all flights in the area) resulted in fatal collisions.
Similar results were reported by Lee (1978b), who found 0.03 to 0.05
percent of the estimated total number of flights near the lines resulted
in collision mortality during periods of good visibility.
Nevertheless, the most dramatic bird kills caused by collisions
with overhead wires are often catastrophic, irregular in time, and hence
unpredictable. A given stretch of line may result in negligible bird
mortality for many years, then suddenly-- during the chance juxtaposition
of a certain flock of birds with certain adverse weather conditions and
a certain disturbance - cause dramatic kills of hundreds of birds over-
night. Thus, it may be argued that specific mortality rates cannot be
quantified, except after many decades of exhaustive study.
While many questions remain unanswered, sufficient information
exists to draw the following qualitative conclusions regarding factors
influencing the probability of wire strikes. This information will
serve to guide our efforts toward mitigation until more quantitative
data become available.
SPECIES OF BIRD
Over 80 species of birds, representing 13 orders, have been documented
as victims of wire strikes or electrocutions in the United States (Table
1). Although this table represents only a small sample of total mortality,
it serves to illustrate the wide variety of guilds, sizes, and behaviors
of birds -- from hummingbirds to swans -- which are vulnerable to this
source of mortality. Scott et al. (1972) reported 74 species killed by
power lines in England. Represented among these species is one order -
Cuculiformes -- not reported in Table 1.
Estimates of relative or absolute numbers of birds of various
species killed by wire strikes are subject to serious limitations.
First, most published accounts of dead birds may be biased toward larger
or light-colored birds, which are more conspicuous, and may also overestimate
rates of losses, as only unusually heavy kills are discovered and published.
Second, reported losses may be only the tip of this iceberg, as only a
very small percentage of the total kill is actually reported; most
casualties are either destroyed by predators, hidden or swept away by
water, or left to decompose along some remote marsh far from the eye of
the biologist.
28
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Table 1. Bird species for which mortality due to overhead wires has been documented in North America.
Order, species, and source of data Indicated Type of
cause of wires .
mortality involved
P0DIC1PEDIFORMES
Horned Grebe (L. S. Thompson unpubl., J. R. Waters unpubl.)
Eared Grebe (D. C. McGlauchlin pers. corim., McKenna and Allard 1976)
Western Grebe (D. C. McGlauchlin pers. comm., McKenna and Allard 1976)
Pied-billed Grebe (Anderson pers. comm., Krapu 1974 pers. comm., D. C.
McGlauchlin pers. comm., McKenna and Allard 1976)
S
S
S
P
P
P
P »T
ro
vo
PELECANI FORMES
White Pelican (G. L. Krapu pers. comm., D. C. McGlauchlin pers. conn.,
McKenna and Allard 1976, Peterson and Glass 1946, J. R. Waters unpubl.,
Willard et al. 1977) 5
Brown Pelican (Willard 1977) S
Double-crested Cormorant (D. C. McGlauchlin pers. comm., McKenna and Allard
1976, von Bloeker 1927, J. R. Waters unpubl.) S
CICONIIFORMES
Great Blue Heron (Lee 1978b, Lano 1927, Willard 1977) E,S
Black-crowned Night Heron (J. R. Waters unpubl.) S
Heron spp. (Boeker 1972) E
Cattle Egret CO- Weise Ders. comm.) S
Egret spp. (Boeker 1972) E
Wood Stork (D. Tiller fide G. Grant) S
Least Bittern (Guillory 1973) S
P
U
P,T
D,P
U
U
u
u
u
F
ANSERIFORMES
Whistling Swan (Willard et al. 1977)
Trumpeter Swan (Banko 1960, H. H. Burgess pers. comm.)
Mute Swan (D. Willard pers. comm.)
Canada Goose (H. H. Burgess pers. comm., McKenna and Allard 1976,
Willard et al. 1977)
S
S
S
U
u
u
-------
Table 1 (cont.)
White-fronted Goose (H. H. Burgess pers. comm., Willard et al. 1977) S U
Snow Goose (incl. Blue Goose) (Anderson 1978, Blockpoel and Hatch
1976, H. H. Burgess pers. conn., G. L. Krapu pers. comm., Peterson
and Glass 1946, Stout and Cornwell 1976, Willard et al. 1977) S D,P
Mallard (Anderson 1978, Krapu 1974, Lee 1978b, D. C. McGlauchlin
pers. comm., McKenna and Allard 1976, Siegfried 1972, Stout and
Cornwell 1976, Willard et al. 1977) S D,P,T
Buffiehead (Lee 1978b) S P
Black Duck (Anderson 1978) S P
Gadwall (Anderson 1978, Krapu 1974) S D,P
Pintail (Anderson 1978, Cornwell 1968, Griffith 1977, Krapu 1974, Lee
1978b, McKenna and Allard 1976, Siegfried 1972, Stout and Cornwell
1976, Willard et al. 1977) S D,F,P,T
Green-winged Teal (Anderson 1978, Coues 1876, Lee 1978b, D, C.
McGlauchlin pers. comm.) S P,T
Blue-winged Teal (Anderson 1978, Cornwell and Hochbaum 1971, Krapu 1974,
g D. C. McGlauchlin pers. comm., McKenna and Allard 1976, Siegfried 1972,
Stout and Cornwell 1976, J. R. Waters unpubl.J S F,P,T
American Wigeon (Anderson 1978, Willard et al. 1977) S P
Northern Shoveler (Anderson 1978, D. C. McGlauchlin pers. comm.,
McKenna and Allard 1976) S P
Wood Duck (Anderson 1978, Stout and Cornwell 1976) S P
Redhead (H. H. Burgess pers. comm., D. C. McGlauchlin pers. comm.,
McKenna and Allard 1976) S P
Ring-necked Duck (Boyd 1961) S P
Canvasback (McKenna and Allard 1976, Willard et al. 1977) S P
Lesser Scaup (Anderson 1978, Krapu 1974, D. C. McGlauchlin pers.
comm, McKenna and Allard 1976, J. R. Waters unpubl., Willard
et al. 1977) S P,T
Ruddy Duck (Krapu 1974, Lee 1978b, D. C. McGlauchlin pers. comm.,
Siegfried 1972, Stout and Cornwell 1976, J. R. Waters unpubl.,
Willard et al. 1977) S D,P
Fulvous Whistling-Duck (McCartney 1963) S U
Common Merganser (Willard et al. 1977) S P
Merganser spp. (Stout and Cornwell 1976, J. R. Waters unpubl.) S U
-------
Table 1 (cont.)
FALCONIFORMES
Red-tailed Hawk (Boeker and Nickerson 1975, Crawford and Dunkeson 1973,
USF&WS unpubl.) ED
Rough-legged Hawk (USF&WS unpubl.) E D
Golden Eagle (Baglien 1975, Boeker 1972, Boeker and Nickerson 1975,
Crawford and Dunkeson 1973, Hannum et al. 1974, Richardson n.d.,
USF&WS unpubl.) E D
Bald Eagle (Boeker 1972, Boeker and Nickerson 1975, Crawford and
Dunkeson 1973, Sprunt et al. 1973, USF&WS unpubl.) E D
Marsh Hawk (J. R. Waters unpubl.) ?
American Kestrel (USF&WS unpubl.) ?
GALL IFORMES
Greater Prairie Chicken (Krapu 1976) S T
Sage Grouse (Borell 1939, Myers 1977) S P,T
Ring-necked Pheasant (Krapu 1974, 0. C. McGlauchlin pers. comm.) S P
w Gray Partridge (Krapu 1974) S T
Turkey (Boeker 1972) E D
GRUI FORMES
Whooping Crane (J. Reed pers. comm.) S
Sandhill Crane (Walkinshaw 1956) S D
Sora (D. C. McGlauchlin pers. comm.) S U
Virginia Rail (D. Kiel and F. Cassel 1978) S P
Black Rail (Emerson 1904) S
American Coot (Anderson 1978, Krapu 1974, Lee 1978b, D. C.
McGlauchlin pers. comm., McKenna and Allard 1976, L. S. Thompson
unpubl., Siegfried 1972, J. R. Waters unpubl., Willard et al. 1977) S P,T
CHARADRIIFORMES
Kill deer (Lee 1978b) S P
American Golden Plover (Krapu 1974) S T
Common Snipe (Lee 1978b, D. C. McGlauchlin pers. comm.) S P
Solitary Sandpiper (Krapu 1974) S T
Least Sandpiper (Emerson 1904, Willard et al. 1977) S T
-------
Table 1 (cont.)
Western Sandpiper (Emerson 1904; Lee 1978b)
Buff-breasted Sandpiper (Krapu 1974)
Marbled Godwit (Krapu 1974)
American Avocet (McKenna and Allard 1976)
Northern Phalarope {Emerson 1904, Willard et al. 1977)
Woodcock (Bailey 1929)
Glaucous-winged Gull (Lee 1978b)
California Gull (Krapu 1974)
Ring-biHed Gull (McKenna and Allard 1976, J. R. Waters unpubl., Willard
et al. 1977)
Laughing Gull (Willard 1977)
Franklin's Gull (D. Kiel and F. Cassel 1978, Krapu 1974, D. C.
McGlauchlin pers. comm., J. R. Waters unpubl.)
Common Tern (McKenna and Allard 1976)
Black Tern (D. C. McGlauchlin pers. conn-, J. R. Waters unpubl.)
COLUMBIFORMES
Rock Dove (L. S. Thompson unpubl.)
Mourning Dove (Lee 1978b, D. Kiel and F. Cassel 1978, Stahlecker
1975)
STRIGIFORMES
Great Horned Owl (Boeker and Nickerson 1.975, Edeburn 1973, Emerson 1904,
Fitzner 1975, McCarthy 1973, USF&WS unpubl.)
Short-eared Owl (Fitzner 1975, L. S. Thompson unpubl., Willard et al.
1977)
Great Gray Owl (Nero 1974)
APOPIFORMES
Allen's Hummingbird [Hendrickson 1949)
PICIFORMES
Yellow-benied sapsucker (Weston 1966)
PASSERIFORMES
Horned Lark (Coues 1876, D. Kiel and F. Cassel 1978, Stahlecker 1975,
L. S. Thompson unpubl.)
-------
Table 1 (cont.)
CO
CjJ
Purple Martin (Anderson 1933}
E
D
Common Raven (Boeker 1972)
E
D
Common Crow (Boeker 1972, Lee 1978b)
E,S
D,P
American Robin (Lee 1978b)
S
P
Thrush (Anderson pers. comm.)
S
P
Bohemian Waxwing (L. S. Thompson unpubl.)
S
F
Starling (Lee 1978b)
S
P
Vireo sp. (Anderson pers. comm.)
S
P
Yellow Warbler (D. Kiel and F. Cassel 1978)
S
P
Western Meadowlark (Coues 1876, D. Kiel and F. Cassel 1978, D. C.
McGlauchlin pers. comm.)
S
-
Yellow-headed Blackbird (L. S. Thompson unpubl.)
s
P
Red-winged Blackbird (Anderson pers. comm., Lee 1978b, McKenna et al.
1976)
S
P
Common Grackle (D. C. McGlauchlin pers. comm.)
S
-
Brown-headed Cowbird (D. C. McGlauchlin pers. comm.)
S
-
Grosbeak (Anderson pers. comm.)
S
P
Song Sparrow (Lee 1978b)
S
P
Savannah Sparrow (D. Kiel and F. Cassel 1978)
S
P
Lincoln's Sparrow (D. Kiel and F. Cassel 1978)
S
P
Chestnut-collared Longspur (D. Kiel and F. Cassel 1978)
S
P»T
McCown's Longspur fCoues 1876)
s
T
Lapland Longspur (Swenk 1922)
S
-
S = wire strike.
E = electrocution.
? = uncertain.
''d = distribution line (less than 50 kV).
F = fence.
P = transmission line (greater than 50 kV)
T = telephone or telegraph line.
U - unspecified power line.
-------
It appears, however, that the most consistent victims of wire
strikes are large migratory water birds of the orders Podicipediformes,
Pelecaniformes, Ciconiiformes, Anseriformes, Gruiformes, and Charadriiformes.
Among these, species whose flocking behavior brings large numbers of
birds together in dense flocks in small wetlands are most frequently
reported. Field-feeding puddle ducks are especially susceptible to
collisions with overhead wires due to the high speed and low altitude of
their flights (Boyd 1961, Krapu 1974, Stout and Cornwell 1976, Wi11ard
et al. 1977). Anderson (1978) found Blue-winged Teal to be more vulnerable
than American Coots or Mallards. Swans, pelicans, cranes, and "white"
geese are also particularly vulnerable due to their great size, low
maneuverability, and flocking behavior (Beer and Ogilvie 1972, Harrison
1963, Ogilvie 1967, Perrins and Reynolds 1967, Sauey pers. comm., Walkinshaw
1956, Willard et al. 1977). Scott et al. (1972) reported that nocturnal
migrants appear to be more susceptible than diurnal migrants. Raptors,
due to their great visual acuity, are rarely the victims of wire strikes
but are vulnerable when distracted or blown off course by gusts of wind.
Whether or not birds of different species are killed in proportion to
their relative abundance has not been shown.
CONDITION OF BIRDS
Most authors concur that young, inexperienced birds, as well as
migrants in unfamiliar terrain, appear to be more vulnerable to wire
strikes than resident breeders. Stout and Cornwell (1976) found negligible
sexual differences in susceptibility of waterfowl. However, Anderson
(1978) found adult Mallards to be more vulnerable than juveniles and
male Blue-winged Teal to be more vulnerable than females.
Many species appear to be most susceptible to collisions when
alarmed, pursued, searching for food while flying, engaged in courtship,
following cones of light at night, taking off, landing, or when otherwise
preoccupied and not paying attention to where they are going (Lee 1978b,
Wi11ard et al. 1977).
WEATHER AND VISIBILITY
Wire strikes appear to be most frequent at night and during windstorms,
snowstorms, periods of heavy fog, or other meteorological phenomena
which reduce visibility and/or cause birds to fly lower. Several researchers,
however, have noted both fatal and nonfatal collisions during periods of
clear, calm, daytime weather when visibility is optimal (Anderson 1978,
Krapu pers. comm., Lee 1978b, Walkinshaw 1956, Willard et al. 1977).
HABITAT ADJACENT TO RIGHT-OF-WAY
Wire strikes of water birds are, of course, most frequent where
lines cross water areas or grainfields used by the birds or where they
separate feeding and roosting areas. Water bird strikes are seldom
reported other than in these situations, but passerines have been found
34
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beneath lines crossing upland habitats (Cassel pers. com., Stahlecker
1975). Gull concentrations near a sanitary landfill were reported by
Lee (1978b) to suffer heavy losses. Willard et al. (1977) suggest that
lines within a single habitat, e.g., a grainfield, are more likely to
cause bird/wire strikes than lines running between different habitats.
TYPE OF WIRES
The physical configuration of lines in space (the strike zone) is
of great importance in determining risks of wire strikes. It is also
perhaps easier to change than the characteristics of birds in attempting
to mitigate losses. Wires of all sorts, including fences, telegraph
lines, telephone lines, power distribution lines, guy wires, and power
transmission lines, have resulted in bird casualties (Table 1). The
small diameter, low (less than 20 feet), high density lines (especially
telephone lines, which may have 20 or more small wires strung between
strucutres, and low-voltage transmission and distribution lines, which
are often underbuilt at various heights on the same set of poles) appear
to be the major source of wire strikes, but they are also much more
abundant than transmission lines. There is some evidence that the large
conductors of extra-high voltage lines are more visible than smaller
conductors or ground wires, especially when strung in bundles, and hence
result in fewer wire strikes (Lee 1978b, Willard et al. 1977). These
extra-high voltage conductors may also alert birds to their presence
through corona discharge and associated noise or by electromagnetic
field effects, although this has not been demonstrated (Lee 1978b) .
The overhead ground, or static, wire is often implicated as a major
culprit in bird losses involving higher voltage lines because birds will
fly over the more visible conductor bundles only to collide with the
relatively invisible, thin static wire (R. Hamilton pers. comm., R. A.
Hunt pers. comm., R. Johnson pers. comm., D. Loomis pers. comm., Scott
et al. 1972, Willard et al. 1977).
OPPORTUNITIES FOR MITIGATION
Transmission line siting is often approached initially by iden-
tifying a corridor, often several kilometers wide, which is broadly
suitable for a transmission line. Corridor selection is followed by
centerline selection, or on-the-ground determination of the precise
route of the line, which in turn is followed by actual engineering and
construction of the line. It is essential to consider mitigation at
each of these three stages of the facility siting process, as described
below. Since very few specific mitigating measures have actually been
implemented and studied, I am unable to present a definitive, state-of-
the-art report as to relative effectiveness. Instead, I will summarize
feasible suggestions and ideas with the hope they will he pursued in
greater depth as a result of this workshop.
CORRIDOR SELECTION
The decision where -- or whether -- to build a new line may be the
most important mitigative tool we have. If it can be shown that broad
35
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geographical areas between proposed endpoints of a new line differ in
risk for wire strikes, mortality can obviously be reduced by staying
away from areas with a high-risk potential. These areas include wet-
lands in general, waterfowl concentration areas, flyways, roosting
areas, feeding areas, low passes, breeding areas, and especially the
paths used for periodic feeding flights. If the area between line end-
points is of uniform impact risk, losses may be mitigated only by not
building the line overhead or by selecting a feasible engineering
alternative with other endpoints.
Corridor selection — depending on the width of the corridor --
provides a very coarse, but nevertheless important, means of mitigation.
If wetlands or other high-risk areas can be avoided by distances of
several kilometers, the probability of catastrophic losses will be
greatly reduced. Unfortunately, moving a corridor to bend around a
critical area increases both the length and cost of the line. Figure 1
shows approximate costs per circuit kilometer of lines of different
voltages and indicates costs involved in deviating from a straight line.
Also, wire strikes are not the only consideration in corridor selection.
They may be treated with low priority when land use, socioeconomic
problems, human populations, and physical characteristics of the land-
scape are simultaneously considered. Thus, even with the best planning,
new corridors may have to include wetlands or other high-risk areas, and
we must look toward other means for mitigation.
CENTERLINE SELECTION
Within a corridor several kilometers wide, there are an infinite
number of possible centerline locations, and centerline placement provides
the opportunity for a much finer degree of spatial mitigation than does
corridor selection. In water bird concentration areas, a four-season
study of the corridor by a waterfowl specialist should be conducted to
determine local movement patterns and optimum line placement. The
studies carried out by Willard et al. (1977) and proposed by Lee and
Meyer (1977) provide excellent models for such investigations. Local
low-level feeding flights are of particular concern, and utilities
should be required to obtain information regarding the size, composition,
seasonality, and frequency of such flights so that flight paths can be
avoided wherever possible.
Several specific mitigative measures involving centerline siting
may be effective where waterfowl concentration areas cannot be avoided.
Scott et al. (1972) suggest line placement parallel rather than perpen-
dicular, to predominant lines of flight. It is also likely that lines
sited adjacent to cliffs, tall buildings, windbreaks, or at the base of
low hills (Figure 2) will result in fewer losses than lines in flat
terrain because birds in flight begin gaining altitude in response to
these highly visible features and, thus, fly well over the lines. Also,
clustering lines, or sharing the same right-of-way with several types of
lines, may be preferable because the network of wires is more visible
36
-------
15 69 100 161 230 345 500
VOLTAGE LEVEL , kV
Figure 1. Estimated costs of overhead and underground power line
installation.
37
-------
juijiiillulJpSZwUUuili
A. High-hazard Situation
x
' - ¦ «U\u •
i/MMiIi
«
-An,,
V
I
B. Corrected Situation
Figure 2. Mitigation by judicious line placement relative to local
topography.
and confined to a smaller area. Birds in flight would have to make only
one climb and descent to cross a cluster of lines, whereas separate
lines require many such maneuvers (Figure 3). However, the hazard to
birds during periods of decreased visibility may be greater where many
lines are clustered together, forming a virtual obstacle course to
flocks flying at many different heights (Figure 4). The relative effect
on mortality rates of separate versus clustered lines depends on many
site-specific factors and deserves careful study.
Another possibility for mitigation involves judicious centerline
placement in relation to local climate. Avoiding areas of frequent and
heavy fog can reduce the probability of wire strikes. It may also be
possible to locate conductors parallel, rather than perpendicular, to
prevailing winds, thereby reducing the likelihood birds will be blown
perpendicularly into wires. Wind roses, as shown in Figure 5, could
provide useful information applicable to centerline placement, although
prevailing wind direction may not be clear in some areas (Figure 5A) or
may differ in the same area between seasons (Figure 5B and 5C). In the
latter example, siting the centerline parallel to prevailing spring
winds would result in crosswinds and a greater probability of wire
strikes in the fall. Wind direction is probably more important in fall
Figure 3. Mitigation by clustering lines at river crossings. Mote
that two climbs and descents are required at A while only
one is necessary at B.
38
-------
B
Figure 4. Separate lines (A) and clustered lines (B). While the
probability of a flock of birds encountering a line is
greater at (A), the risk of collision in a flock of
birds passing through the lines during poor visibility
is greater at (B).
39
-------
A
B
C
Area I
Area II
Spring
Fa 1 1
Figure 5. Hypothetical wind roses for two areas, the first (Area I)
showing little predominance of wind direction and the second
(Area II) showing strong seasonal predominance of direction
which differs from spring to fall. Direction of lines indi-
cate wind direction in each of 16 compass points, and length
of lines indicates the percentage of time the wind blows in
that direction.
than in spring, because hunting pressure has been shown to increase the
nocturnality of duck movement (Willard et al. 1977). This type of
mitigation is probably most applicable to lines in river canyons where
winds are topographically confined yearlong to a certain direction
(Figure 6).
MITIGATION BY ENGINEERING DESIGN
The following mitigative measures may be applicable both to de-
signing new lines and to reducing losses on existing lines which are
causing considerable bird mortality and which cannot feasibly be moved.
Underqrounding
If conductors are buried, the chances of wire strikes are, of
course, reduced to zero. This is quite feasible for telephone and power
distribution lines, and in certain cases it may actually be cheaper than
overhead construction. However, as voltage rating increases, cost
increases exponentially, and risk for detrimental impacts to resources
other than waterfowl may also increase significantly (Schiefelbein
1977). Figure 1 compares costs of overhead and underground transmission
for a variety of voltages, based on currently available technology.
Termination costs, or the costs of "going under" at each end of the
underground segment, are considered separately as these are roughly the
same regardless of line length. (Total underground costs are calculated
from Figure 1 by multiplying the cost per unit length by total length
and adding twice the indicated termination costs.) Technology has been
proven only for voltages of 69 kV and below; high voltage underground
40
-------
Figure 6. Where winds are confined by topography, as in major river
canyons, wire strikes can be mitigated by line placement
parallel, rather than perpendicular, to wind direction and
by crossing the river obliquely rather than perpendicularly.
In this figure, A is preferable to B or C.
technology is presently in the prototype stage. In fact, out of 5373
miles of 100 kV lines projected over the period 1976 to 1981, only 56
miles are planned as underground (Federal Power Commission Bull. 22175,
26 February 1976). Less than one mile of gas-insulated, prototype,
underground, 500 kV transmission line has actually been built (Ray pers.
comm.).
Tower Design
For 500 kV metal-lattice towers, two basic tower designs are available
guyed and free standing (figure 7). Guyed towers are relatively lightweight
and are used exclusively as suspension towers, that is, towers which
simply hold the wires off the ground. The guy wires leading from these
towers may pose an additional collision hazard, which can be mitigated
by using self-supporting towers at river crossings or in wetlands.
Self-supporting towers are also used as suspension structures, but the
larger and sturdier designs may be used as dead-end structures, capable
of withstanding a strong lateral pull from unbalanced conductor tension.
Although the range of costs of self supporting towers ($24,000 to $72,000)
is greater than that of guyed towers ($18,000 to $23,000), self-supporting
towers are often required at water crossings, since the long spans
involved require greater tower strength.
Presence of Static Wires
As mentioned above, the static wire is smaller and hence less
visible than conductors on higher voltage lines, and it appears to be a
major cause of collision mortality. This hazard may be reduced simply
by eliminating the static wire from spans crossing wetlands. However,
41
-------
500 KV SINGLE CIRCUIT TOWER - SELF SUPPORTED 500 KV SINGLE CIRCUIT TOWER - GUYED
DELTA CONFIGURATION DELTA CONFIGURATION
Figure 7. Self-supported and guyed 500 kV tower designs.
there are two major objections. The purpose of the static wire is to
intercept and drain the electrical charge from a lightning strike; if
the wire is not present, the lightning bolt can strike conductors and
cause relays to trip out. Indeed, lightning appears to be the major
single cause of power!ine outages in the U.S. (Schiefelbein 1977). In
many areas, charts of lighting frequency are available, and the probability
of lightning strikes on a given span may be calculated. Even in areas
of low lightning frequency, eliminating the static wire will slightly
increase the probability of lightning-caused outages. Since eliminating
the static wire over a certain span causes lateral stress on the towers
at the ends of the span, dead-end structures, at a greatly increased
cost, would be required. This increased cost could be somewhat offset
by savings in the price of the static wire, which has been estimated by
Bonneville Power Administration to exceed $13,000 per mile of single-
circuit 500 kV line (Schiefelbein 1977).
Height of Conductors
One suggested means of mitigation is to adjust the height of conductors
above ground to avoid predominant approach flight path heights of those
42
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birds using nearby water areas. However, there are several serious
problems with this approach. First, flying heights and approach patterns
of birds vary greatly by species, season, and weather conditions. Birds
which fly at great heights during clear, calm weather may fly very close
to the ground during periods of poor visibility and thus be vulnerable
to wires of varying height. Also, conductors sag in the middle and may
be over twice as high near the tower as at mid span. Upper and lower
bounds are put on the available range of heights of conductors by the
increasing costs of taller towers and by mirnmum ground clearance
standards, respectively (Table 2).
Table 2. Approximate minimum ground clearance for power lines of
different voltages.
Voltage (kV) 15 69 115 161 230 500
Clearance (ft) 22 24 25-27 27-29 30-31 35
Clearance (m) 6.7 7.3 7.6-8.2 8.2-8.8 9.1-9.5 10.7
Some advantage may be gained by installing conductors on the highest
towers possible because wire strikes are often associated with low
visibility. This may cause additional problems, though, with species
reluctant to fly under the conductors, thereby increasing their chances
of collision with the static wire, not to mention the problem of increased
cost.
Where lines cross forested lands, tower height can sometimes be
reduced to that of the trees, reducing above-canopy exposure and thus
lowering the risk of collision to birds flying over the treetops (Figure
8). This requires shorter spans and more towers to maintain minimum
ground clearance, and it may be costly. Losses might be reduced by
keeping all lines between towers in roughly the same horizontal plane,
that is, employing a flat conductor configuration rather than a delta or
stacked configuration. This effectively reduces the vertical dimension
of the potential strike zone. To be effective, however, the static wire
must remain above the plane of the conductors.
Increasing Visibility of Wires
Measures which increase the visibility of wires (especially static
wires) would theoretically decrease the probability of birds colliding
with the wires. Daytime wire visibility may be enhanced by increasing
the diameter or by changing the color or reflectivity of the wire.
Collision hazard seems to be roughly inversely proportional to wire
diameter, and although larger diameter conductors are preferable electrically,
they are also more expensive and require stronger towers. Stringing
conductors in bundles, a common practice for higher voltage lines,
43
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A. High-hazard Situation
B. Corrected Situation
Figure 8. In areas where flocks of birds commonly fly just above the
forest canopy, wire strikes can be mitigated by placing the
lines just below treetops. The horizontal, dotted line
indicates minimum ground clearance of the conductors, and
lowering the line while maintaining this clearance requires
more towers and shorter spans.
increases apparent conductor diameter and hence visibility. No information
is available on the relative visibility of different color wires to
birds, although dark wires would probably be most visible against an
overcast sky and bright, reflective wires would likely be most visible
on sunny days.
Visibility of wires may also be increased by attaching highly
visible objects to them. Large, colored spheres of the type frequently
used on lines near airports or on long, high spans may be installed at
a cost of approximately $100 each. While birds may very well see these
spheres, they may still fail to see the wires between and may strike the
wires while swerving to miss the spheres. Scott et al. (1972) reported
that 15 cm black tapes tied at 1.9 m (6-foot) intervals along static
wires were effective in reducing bird casualties in England. The same
authors reported an experiment in England in which static wires were
marked at 1.2 m (4-foot) intervals with 5 cm bands of luminous orange
tape, or with luminous orange strips having a free-hanging tail 5 cm
long. Casualties were somewhat lower on marked spans during the 3 years
after marking than during the preceding 3-year period. The number of
casualties at marked spans was also lower than adjacent unmarked spans
during the 3 years after marking. However, differences were not significant
and were probably overriden by effects related to line placement. The
relative effectiveness of the two marking techniques could not be determined,
and the orange strips faded to white 18 months after marking. Marking
44
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wires with other devices such as ribbons, streamers, flags, or even
plastic windmills of the type seen in used car lots may be effective in
reducing losses and should be tested in the future. Disadvantages of
this type of mitigation are the aesthetic impact of such marking and
nighttime ineffectiveness.
Wire visibility may be increased at night by attaching reflective
or luminous objects to the wires or by giving the wires a reflective or
luminous coating and providing a nighttime light source. The expense
and logistical problems of illuminating long spans of transmission lines
would be formidable, and there is some evidence that night floodlighting
may be counter effective. Several authors (Avery et al. 1976, Cochran
and Graber 1958, Johnston and Haines 1957, Laskey 1960, Rybak et al.
1973, Weir 1976) found that nocturnally migrating birds are attracted to
the "white hole" created by a bright beam of light; they become blinded
or disoriented, often flying around within the beam for hours or until
exhausted or killed by striking objects. Avery (pers. comm.) and Weir
(1976) suggest that strobe lights may be much more effective than flood-
lights in reducing collision mortality, although in at least one case
(Whelan 1976) strobes did not provide an improvement over continuous
light. Some evidence suggests red strobe lights may be preferable to
white (Weir 1976), but much work is needed to determine optimum frequency,
color, intensity, direction, and location relative to the lines. One
manufacturer, Flash Technology of America (pers. comm.), has developed a
strobe model (FTB-205 B) specifically for use on transmission towers.
Nighttime illumination of wires has not been adequately tested; it
certainly could not be expected to prevent losses due to the preoccupation
of startled or flocking birds or to birds being thrown off course by
gusts of wind.
Repelling Birds from the Vicinity of Conductors
The probability of wire strikes can be reduced if the birds are
somehow kept away from the vicinity of the lines. This may be accomplished
by making habitat near the lines relatively less attractive than habitat
farther from the lines (as discussed above) or by chasing or scaring
birds away from the lines with some sort of auditory or visual stimulus.
Wind-operated whistles or bells have been suggested, but they would
probably be of limited effectiveness. A device known as Av-alarm, which
produces high-frequency "distress" sounds effective in repelling certain
species of birds, has been used in connection with TV towers and airport
ceilometers with limited success. These devices are rather expensive,
of unknown effectiveness in repelling water birds (which may habituate
to a constantly repeated sound), and impractical to install along long
lengths of power!ine. Windmills or wind-animated scarecrows made to
resemble hunters, canids, or raptors may be effective in repelling birds
during daylight hours. Raptor silhouettes cut from paper have reduced
avian collisions with a glassed-in walkway in Pullman, Washington (Johnson
and Hudson 1976), and owl dummies have reduced the number of pigeons
roosting on an interstate highway bridge just east of Seattle, but
similar devices to repel waterfowl have not been tested. Encouragement
of raptor nesting on towers as a waterfowl deterrent merits study.
45
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A problem with this type of mitigation is that otherwise attractive
habitat is rendered unavailable to a segment of the bird population,
forcing it into less suitable habitat elsewhere. This may have an
effect on carrying capacity as great as, or greater than, wire strike
mortality and may render this type of mitigation counterproductive.
Again, no data are available to document this supposition.
Shielding Structures
If wires can be screened by trees, billboards, or other man-made
structures, it is quite likely collisions can be reduced or prevented.
Many bird species are reluctant to fly under objects, and ducks in
particular begin gaining altitude well ahead of an obstacle in their
path (Fog 1970, Gunter 1956). Shelterbelts, bridges, billboards, high
wooden fences, or other highly visible structures can force birds to fly
over lines even if they cannot see the wires (Figure 9). These flight
path barriers could probably be effective even if much lower in height
than conductors or if some distance from the right-of-way, provided they
are located optimally along the flight path of the birds. Further study
of the behavior of birds in relation to obstacles in their flight path
would allow optimum placement of such barriers. Of course, such structures
would have to be designed to prevent birds from colliding with them, and
they have the potential of being eyesores. This type of mitigation
would probably be most effective for smaller lines (especially telephone
and distribution) or at multiple-line river crossings.
Preventing Distraction of Birds
It has been noted that birds are highly vulnerable to collisions
when startled or distracted. Prohibiting hunting or travel (perhaps by
closing access roads parallel to lines through wetlands) may serve to
reduce collision losses.
Figure 9. Mitigation by placing highly visible structures next to the
line to alter flying height of birds.
A. High-hazard Situation
B. Corrected Situation
46
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Mitigation by Habitat Modification
If the habitat factors which make certain power!ine rights-of-way
attractive to birds are known, the opportunity exists to mitigate wire
strikes by making certain habitats relati vely less suitable or attractive
to high-risk species. I emphasize relatively since it may not be desirable
to degrade right-of-way habitat quality, and hence carrying capacity,^
simply to lower mortality rates -- no one is going to recommend draining
or filling a wetland crossed by a powerline simply to lower the incidence
of collision mortality. Perhaps a better approach would be to make
nearby habitat more attractive, thereby not only attracting birds away
from a high-risk situation but benefiting the population as well. This
means may be particularly effective with respect to feeding flights; in
cases where feeding and roosting areas are separated by a power line,
it may be advantageous to create new feeding and resting areas, as shown
in Figure 10. Lee (1978b) mentioned large kills of gulls flying between
a wetland and a sanitary landfill-, changing the location of the landfill
could reduce these losses. Although these measures may be expensive,
they may very well be less expensive and.more beneficial than some of
the contrived engineering solutions noted above. They will certainly
not be applicable however, in all situations.
A corollary measure involves changes in local land use patterns on
and near the right-of-way in order to change local flight patterns of
migratory birds. For example, reversing the locations of a grainfield
used as a feeding area and an alfalfa field (Figure 11) may reduce
collision mortality. Willard et al. (1977) found that grainfields in
the Klamath Basin of Oregon were more attractive to waterfowl than were
pastures, especially just before or just after harvest, and that plowing
greatly reduced attractiveness while flooding increased it. It is thus
possible to remove or relocate the feeding enticement by changing the
timing or location of flood irrigation.
Experience has shown that landowners are often reluctant to make
such dramatic changes voluntarily, and it would be difficult to force
them to do so outside the right-of-way. Consequently, these habitat
changes may be most practical on public land or along multiple corridors.
Also, traditional flight patterns may be difficult to change through
habitat modification.
SIGNIFICANCE OF WIRE STRIKES
The "significance" of an adverse impact to wildlife really incor-
porates two distinct concepts—bioloigcal significance and social
acceptability (Buffington 1976). A biologically significant impact is
one which is long-term and which results in a measurable change in
carrying capacity or ultimate population size. In this respect, the
impact of wire strike mortality on bird populations can be judged bio-
logically significant only if it exceeds the compensatory response
capability of the population and thus results in a measurable population
decline. That this is the case with any waterfowl species is highly
doubtful, since waterfowl populations are able to compensate for sub-
stantial hunting mortality, which is much greater than collision mortality
47
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1
A. High-hazard Situation
B. Corrected Situation
Figure 10. In some cases, local feeding flight patterns may be changed
by creating new feeding and/or resting areas.
Figure 11. Mitigation by local land use change. Reversing the locations
of attractive and unattractive land uses in the vicinity of a
power line may change waterfowl feeding flight patterns.
(Anderson and Burnham 1976). Stout and Cornwell (1976) estimate that
wire strikes comprise about 0.1 percent of total waterfowl nonhunting
mortality in their sample; hunting mortality, in comparision, probably
affects 20 percent to 30 percent of waterfowl populations (Anderson and
Burnham 1976, McGregor pers. comm., Willard et al. 1977). Losses of
certain rare species with lower compensatory ability may indeed be
biologically significant; the loss of five Whooping Cranes to wire
strikes could be disastrous to the population. The extent of our know-
ledge today is such that we may not be able to perceive or measure
changes in carrying capacity attributable to wire strikes, even if they
are sizable and long-term.
Should wire strikes be found not to significantly affect population
size over the long-term, they may be important in another respect,
48
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namely, social acceptability. The public sensitivity may be so affronted
by the loss of 10 Whistling Swan that this loss constitutes a very real
social impact and is deemed by society to be unacceptable, although the
loss may not be biologically significant. The recent public outcry
over the proposed Midpoint to Medford 500 kV lines (which would cross
Oregon's Klamath Basin, a very important waterfowl concentration area)
illustrates this point well. The public simply does not want to see
birds killed by power lines, regardless of the biological significance
of such losses.
The concern has also been raised that, while losses may not affect
ultimate population size, they may reduce the harvestable surplus of
waterfowl available to hunters. The assumption that nonhunting mor-
tality is largely replaced by hunting mortality may not be true above
certain threshold values (Anderson and Burnham 1976, Stout and Cornwell
1976), and post-hunting season mortality may have an important effect on
populations. Cornwell (1968) believed that wire strike losses add to,
rather than replace, hunting mortality.
It may be relevant at this point to bring up the concept of maximum
sustainable yield (see Sharma 1976 for a discussion of this concept in
relation to impact significance). If we assume that a fixed proportion
of the population of migratory birds can and will be lost to various
types of mortality (predation, disease, starvation, shooting, wire
strikes, etc.) each year without affecting carrying capacity -- that is,
the maximum sustainable yield -- we may allocate certain portions of
this harvestable surplus to the various sources of mortality (Figure 12)
and manage accordingly.
Figure 12. The maximum sustainable annual mortality of populations can,
to some extent, be differentially allocated to specific
types of mortality without affecting carrying capacity or
long-term population size. (Modified from Sharma 1976.)
49
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Society may deem wire strike mortality to be an unfortunate but
unavoidable phenomenon and thus allocate a certain percentage of the
harvestable surplus to these losses rather than accept the costs of
mitigation. This nonaction amounts to saying that a certain amount of
wire strike mortality is part of the cost society must pay for a con-
venient source of energy. If carrying capacity is to remain constant,
the magnitude of other types of mortality will have to adjust downward.
This includes hunting mortality, and the social impact of reduced avail-
ability of waterfowl to hunters hardly needs mention.
On the other hand, wire strike losses may be judged unacceptable,
and society must then attempt to channel money, energy, and resources
into efforts to mitigate or prevent losses. Society is then faced with
the problem of optimizing the balance between various social costs of
mitigation and the benefits of reduced wire strike mortality.
COSTS VERSUS BENEFITS OF MITIGATION
A couple of hypothetical examples may best serve to illustrate the
difficulty of balancing the costs and benefits of mitigation. Let us
assume we could accurately predict the rate of wire strike mortality of
a proposed twin 500 kV transmission line through the center of a circular
wetland 10 km in diameter to be 100 kg of waterfowl per km per year. In
order to skirt this wetland completely, each line would have to be
increased in length by (1 Ott/2 -10) km or 5.7 kilometer. The increased
cost of doing so, assuming a cost of $125,000 per km, would be $1,425,000.
This compares with 80,000 kg of waterfowl that would be "saved" assuming
a 40-year life of the line (100 kg per circuit kilometer-year times 2
circuits times 10 km times 40 years). Thus, the cost to society per
kilogram of waterfowl would be $17.81. This may be unreasonably expensive,
especially since the losses may not be biologically significant and the
"lost11 waterfowl are never actually recovered.
For another example, let us consider a pond 0.1 km wide which will
be spanned by a 500 kV line using 23 m guyed structures on each side.
Using the same hypothetical rates of wire strikes noted above, approx-
imately 400 kg of waterfowl would be lost over the 40-year life of the
line. Assuming these losses could be prevented by eliminating the
static wire, thus requiring self-supporting towers which are (by best
1977 estimates) approximately $100,000 more expensive to install,
society is, in effect, paying $250 per kilogram of waterfowl. If losses
could be prevented by installing colored flags on the guy wires at a
cost of $1,000, the cost to society could be reduced to $2.50 per kilogram
of waterfowl.
These may be artificial examples, but they serve to illustrate an
important point: Costs of mitigation must be weighed carefully against
the benefits to be obtained. This problem is sufficiently difficult to
solve under any circumstances, but it is compounded by the fact that
wildlife values (despite several recent attempts) are essentially
unquantifiable. What is the value of a duck, a cormorant or a Whooping
Crane? The U.S. recently settled a Canadian claim for ducks killed by
an oil spill by paying the Canadian government $2 per duck (Efford
50
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1976), and the possibility exists that utilities may be required to
reimburse the public a dollar value for waterfowl losses attributable to
wire strikes. But what is the monetary value of a lost opportunity for
a hunting experience? In another recent case, the court awarded a
wetland owner $90,000 damages for alleged avoidance by birds of his land
because of nearby power!ines (Bonde 1970).
Obviously, whatever the value of waterfowl, the point is ultimately
reached where further investments in mitigating measures yield diminishing
returns in terms of waterfowl abundance. Long before this point is
reached, serious consideration should be given to compensation of wire
strike losses as an alternative to mitigation.
COMPENSATION AS AN ALTERNATIVE TO MITIGATION
In the example of the 500 kV lines through a circular wetland,
$1,425,000 was the cost estimate of mitigation through center!ine place-
ment, and the benefits to be obtained amounted to 2,000 kg of waterfowl
saved annually. If the line were built as originally planned, through
the center of the marsh, the money is saved while the ducks are lost.
What benefits could be obtained by using this same amount of money
instead for waterfowl habitat improvement, wetland acquisition, winter
feeding, law enforcement, or other long-term increases in carrying
capacity? It is likely they could far exceed the benefits to be obtained
by merely preventing a relatively small percentage of nonhunting mortality.
While compensation is an attractive alternative to mitigation, it
is not the final answer, especially where "out-of-kine" compensation is
involved. No amount of Mallard habitat improvement can compensate for
the loss of a flock of Whooping Cranes to wire strikes. Serious logis-
tical difficulties may be encountered by efforts to compensate Snow
Geese losses in the U.S. by improving breeding habitat in Canada, al-
though Pacific Power and Light is considering a proposal by Ducks
Unlimited to compensate for collision losses in Oregon by contributing
$248,000 to habitat acquisition in Canada. Problems in forcing utilities
to make such compensation would be formidable. Nevertheless, it is an
alternative which, in some cases, would yield greater benefits than
mitigation and should be considered on a case-by-case basis.
The point is not that mitigation is unimportant. The point here is
simply that creating additional habitat may, in some cases, be a better
use of available money than developing more and more sophisticated and
energy-intensive "technological fixes" such as strings of lights or
electronic noisemakers.
SUMMARY AND CONCLUSIONS
Transmission line wire strikes by migratory birds are an increas-
ingly serious problem in the United States. While a great many species
are affected, large water birds are the most consistent victims and
losses are heaviest in waterfowl concentration areas during periods of
51
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wind, fog, rain, or nighttime feeding activity. Initial siting of lines
away from hazard areas is perhaps the most direct approach to mitigation
but cannot always be implemented because of other siting constraints.
Where lines cross high-risk areas, losses may be reduced by a variety of
means, including underground installation, changes in tower design,
removal of static wires, changes in conductor height, increasing wire
visibility, repelling birds from the vicinity of conductors, installing
shielding structures, preventing distraction of birds, and local habitat
modification. Most of these mitigating measures have not been tested,
but the most promising short-term solutions appear at this time to be the
following: marking wires (especially static wires and guy wires) with
permanent, highly visible flags or strips; changing flight patterns of
birds by installing highly visible banners parallel to the lines or by
altering land use patterns adjacent to the right-of-way, and clustering
lines at river crossings. The biological significance of wire strikes
may not be great, but the public relations value to utilities of at-
tempting mitigating measures may be high. The costs of many potentially
effective mitigating measures outweigh the benefits to be obtained, and
in some cases compensation by habitat improvement may be preferable to
mitigation. Priorities for future research should be the evaluation of
rates, causes, circumstances, and populational significance of wire
strikes on different types of lines (with particular reference to the
importance of the static wire); development of wire markers, warning
devices, or alternative tower designs which are effective but not pro-
hibitively expensive; and exploration of the many untested mitigative
measures discussed above.
ACKNOWLEDGEMENTS
I extend my sincere thanks to the many individuals who took time
to discuss this topic with me and whose ideas form the bulk of this
paper. Much of the material presented here was gathered during the
course of transmission line impact evaluations carried out by the Energy
Planning Division, State of Montana.
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EFFECTS OF TRANSMISSION LINES ON BIRD FLIGHTS: STUDIES OF BONNEVILLE
POWER ADMINISTRATION LINES
Jack M. Lee, Jr.
Bonneville Power Administration
INTRODUCTION
Bonneville Power Administration {BPA) is the agency within the U.S.
Department of Energy responsible for marketing power generated by Federal
hydroelectric dams in the Columbia River Basin. BPA operates over
19,000 km of transmission lines (115 kV to 500 kV AC, + 400 kV DC)
located throughout the Pacific Northwest. As a Federal agency, BPA is
subject to provisions of the National Environmental Policy Act which
require that the environmental impact of major actions be identified.
In 1974, BPA began a research program to obtain specific information
on the environmental impact of transmission facilities. The program was
designed to be responsive to concerns identified during the environmental
impact statement process by BPA, other agencies, and the public. Initial
research was directed at the impact of extra high voltage (EHV) (above
230 kV) transmission lines on plants and animals (Goodwin 1975, Lee and
Rogers 1976, Griffith 1977). This reflected the wide interest in the
possible biological effects associated with corona and electric and
magnetic fields of EHV transmission lines. To date, this research has
shown that most impacts on wildlife that are detectable by field observation
are due primarily to habitat modifications resulting from construction
and maintenance operations (Lee 1977).
In recent years, a growing number of comments on the possible
effects of BPA transmission lines on migratory birds have been received.
The comments have been primarily in the form of questions rather than
reports of observed effects. Research on the BPA system so far has
concentrated on possible effects of transmission lines on bird distri-
bution and abundance (Lee and Rogers 1976, Lee and Griffith 1978,
Griffith 1977) and on the use of transmission line structures as nesting
sites (Lee 1976). Preliminary information has also been collected on
the effects of transmission lines on bird flight behavior, including
collisions with wires. This last subject has received considerable
attention in recent years, and the need for quantitative data is generally
recognized. In this paper, I will point out the distinguishing charac-
teristics of transmission lines, briefly review relevant literature» and
report on studies and observations of the effects of BPA transmission
lines on bird flight behavior and collision mortality.
53
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TRANSMISSION LINES
Transmission lines are used to transmit electric power from genera-
tion sources to load centers. In 1975, there were an estimated 408,930
Qircuit ion of overhead transmission lines (in this group 100 kV to 800
kV) in the U.S. with EHV (345 kV to 800 kV) lines constituting approximately
6.3 percent of this total (Edison Electric Institute 1976). Currently,
the highest voltage for operational a.c. transmission lines in the U.S.
is 765 kV. BPA has constructed a 1200 kV AC prototype transmission
line, and such ultra high voltage (above 800 kV) lines are expected to
be in use in the 1980's.
Compared with power distribution (below 115 kV) and communication
(telephone and telegraph) lines, transmission lines usually have much
larger support towers and conducting wires (conductors) (Figure 1). At
voltages above 345 kV, multiple conductor bundles are usually used. For
example, the 4.07 cm diameter conductors used on high capacity BPA 500
kV lines, which are in bundles of three for each of the three-line
phases, are over four times larger than the single conductors used on
some 12.5 kV distribution lines. The conductors on the BPA 1200 kV
prototype line are 4.07 cm in diameter, and there are eight of them in
each phase arranged in 1.1 m diameter circular bundles. On some transmission
lines, one or two overhead groundwires (also referred to as shield wires
or static wires) are used for protection against lightning. These are
usually of small diameter compared with conductors.
For EHV lines, effects form the electric and magnetic field and
from corona are more apparent than from lower voltage lines (Lee et al.
1977). The calculated electric field strength at conductor height at
1 m, 10 m, and 50 m from the conductors of a 230 kV AC transmission line
is about 20 kV/m, 1.3 kV/m, and 0.05 kV/m, respectively. For a 500 kV
line at these distances, these values are approximately 70 kV/m, 4.3
kV/m, and 0.3 kV/m, respectively. For comparison, the DC electric field
strength of the earth is about 0.13 kV/m at the surface (Polk 1974).
Magnetic field strength is a function of current rather than voltage as
in the case of the electric field. At distances greater than about 10 m
field strength is usually of less magnitude than the 0.6 Gauss of the
earth's DC magnetic field (average in fair weather).
Corona occurs when the electric field on the surface of a trans-
mission line conductor exceeds the breakdown strength of air (Deno and
Comber 1975). Audible noise and flashes of light are among the products
of corona. With a.c. transmission lines, corona is most noticeable
during inclement weather. The noise consists of a broadband hissing,
crackling component with a 120 Hz tone or multiples of this frequency
occasionally present. The amount of audible noise produced by transmission
lines varies considerably depending on a number of factors including
weather, voltage, and conductor configuration. With BPA's present 500
kV line design, audible noise during rain averages about 50 dB(A) at the
edge of the right-of-way.
54
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Figure 1. Configurations of typical BPA transmission towers. For
comparison, a typical 125 kV distribution line pole, 10.4
m high, is shown to the left of each transmission tower.
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LITERATURE REVIEW
Bird deaths due to collisions with power lines have been documented
in several reports (Table 1). In a number of reports, there is insuffi-
cient information with which to determine whether the line involved was
a transmission or distribution line. Terms such as "power lines" or
"overhead lines" are frequently used without qualification, and the
latter can include communication lines. As a comparison with the
reports in Table 1, I found at least nine reports which describe bird
collisions with distribution lines and five reports which do not dis-
tinguish between power and communication lines. (An annotated bibliography
listing these reports is available from the author.) It should be
pointed out that in some reports the birds found dead beneath distri-
bution lines may have been electrocuted. Electrocution is generally not
a problem with transmission lines because of the greater distance
between conductors.
In general, reported mortality levels due to bird collisions with
transmission and even distribution lines are low compared with those
reported for certain other types of obstacles (e.g., television trans-
mitting towers) as described in reviews by Vosburgh (1966) and Weir
(1976). Currently, it is not clear how "reported" mortality due to
collisions with various obstacles compares with actual mortality.
Table 1. Reports of bird collisions with transmission lines and with
'^owerlines" which may have included transmission and/or
distribution lines.
Reference
Line type
Location
No. birds found
Circumstances
Anderson
1978
Two 345 kV trans-
mission lines
Central Illinois
343 dead or crippled
waterfowl
Birds were found in a water-filled
slag pit near lines during the fall
over a 3-year period. Anderson
estimated approximately 400 birds
killed each year during fall and
winter.
A rend
1970
500 kV transmis-
sion line
Sutter N.W.M.A..
California
50 ducks
Birds apparently startled into flight
by Illegal hunters at night.
Scott et
si. 1972
Two 400 kV trans-
mission lines
Dungeness, Great
Britain
1,285 birds of 74
species
Birds found near three line spans
between January 1964 and November
1970. Actual number of casualties
estimated at 6,000.
W11 lard et
al. 1977
230 kV transmis-
sion line
Klamath Basin,
Oregon
lc waterfowl and
shorebirds
Birds were found at three sites during
searches conducted during fall 1976
and spring 1977.
Blokpoel S
Hatch 1976
"Power line"
Manitoba, Canada
An estimated 25-75
Snow Geese
Light airplane startled birds into
flight.
Go!lop
1965
"Power lines"
Saskatoon,
Canada
15 birds of 12
species
Birds found during one fall where
series of powerlines crossed sandbar.
Krapu
1974
"Power lines"
North Dakota
15 birds
Mortality includes Krapu's own obser-
vations over several years plus re-
ports from other persons.
Stout
1967
"Power lines"
California
235 Ruddy Ducks
Report did not indicate when col-
lisions occurred other than that
losses were greatest during fcggy
periods.
56
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Reported collision mortality due to wire strikes has been related
to other nonhunting mortality in waterfowl by Stout and Cornwell (1976).
In their paper, reported mortality due to collisions with objects account-
ed for 2,299 (0.1%) of the 2,108,880 birds in their sample. Of the
former number, 1,487 were reported collisions with telephone and power
lines. Cornwell and Hochbaum (1971) have pointed out bird collisions
with lines largely go unnoticed and unreported. This can probably also
be said of many other types of collisions.
Concerns have also been expressed which are somewhat contradictory
to those related to the collision potential of transmission lines.
During a court case involving an Illinois duck hunting club and a power
company, witnesses testified that transmission lines adversely affected
waterfowl hunting near the line (Anon. 1968). Similar testimony was
given during a 1977 court case in Washington State (United States vs.
Chadbourne). This latter case involved a BPA 500 kV transmission line
which was constructed across land leased by a private duck hunting club.
In both of these cases, the court, in effect, found that a transmission
line would have some adverse influence on waterfowl flight behavior
resulting in adverse effects on waterfowl hunting near the line. The
possibility that power lines could change waterfowl hunting success was
also suggested in a study of the interaction between birds and obstacles
by Willard and Willard (in press).
These reports and testimony raises the question as to whether birds
react to the electrical effects of transmission lines. There is evidence
that birds can at least perceive such effects. The range of frequencies
heard by most birds is very similar to man's range (Bremond 1963), and
it is reasonable to assume that corona noise is audible to birds. Although
birds are commonly seen perched on distribution and communication lines,
I have never seen a bird attempt to land on an energized transmission
line conductor. Unsuccessful landing attempts have been reported to me
on a few occasions. Graves et al. (1978) reported that, in a laboratory
test, pigeons were apparently able to detect a 60 Hz electric field of
32 kV/m (the lowest field strength tested). This is the field strength
at approximately 2 m from the conductors of a 500 kV line. Two reports
have indicated birds are able to perceive electric and magnetic a.c.
fields at levels comparable to those of the earth's d.c. fields (Southern
1975, Larkin and Sutherland 1977.)
STUDIES OF BPA TRANSMISSION LINES
Prior to the start of a study in October 1977, which is described
below, most observations of the effects of BPA transmission lines on
bird flights were made incidentally to collecting other biological data.
For example, during a 13-month study of the +400 kV DC Intertie in
Oregon, Griffith (1977) observed a juvenile pintail sustain fatal injuries
by colliding with the overhead groundwire. Visibility was good at the
time of the collision. One of the duck's eyes had an opaque appearance
which did not appear to have been caused by the collision. On another
occasion, Griffith and I watched a turkey vulture collide with a conductor
57
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of a 230 kV line located adjacent to the DC line. This collision also
occurred when visibility was good, although in this case the bird
apparently was not seriously injured.
Griffith's study was not specifically designed to provide information
on bird collisions; however, after several hundred hours of field observa-
tions and after traveling hundreds of kilometers on the right-of-way
access road, he found only five dead birds, some of which may have
collided wth the line. The DC Intertie line has metal towers approximately
36 m tall and two sets of 4.47 cm diameter conductors in bundles of two.
The line also has a single overhead groundwire. Most of the line is
located in western juniper and sagebrush, and only a few small areas
utilized by waterfowl are crossed.
I made an interesting observation while conducting breeding bird
counts on the right-of-way of two 500 kV transmission lines in central
Oregon. A Golden Eagle being chased by two Common Ravens collided with
the conductors on one of the 500 kV lines. Although the bird exhibited
some erratic flight behavior after the collision, it did not appear to
be injured. The line had two 4.07- cm diameter conductors for each
phase. The most extensive bird collision mortality which has been
reported for a BPA transmission line occurred near Portland, Oregon, and
involved a 230 kV line. This study is described below.
BIRD COLLISIONS WITH A 230 KV TRANSMISSION LINE
On January 1977 while observing bird flights near Bybee Lake, I
began finding birds between towers 7/2 and 6/6 of the BPA Ross-St. Johns
230 kV transmission line (Figure 2). The line carries two electrical
circuits (double circuit). Between structure 6/6 and the St. Johns
Substation 2.5 km to the southwest, there is a single 1.6 cm diameter
overhead groundwire. Overall dimensions of the steel support towers and
conductro configurations are shown in Figure 2. Each of the six conductors
is 2.7 cm in diameter and consists of outer aluminum wire strands and
inner steel strands. At midspan, the lowermost conductors are approximately
20 m above the ground. At the Bybee Lake crossing, the lowest conductors
are about 25 m above the water. The line was energized in 1952.
A 115 kV transmission line operated by Portland General Electric
Company (PGE) runs parallel to the BPA 230 kV line. The 115 kV line has
three 2.6 cm diameter conductors spaced 3.8 m apart on a horizontal
plane. The conductors are supported by wood pole, H-frame structures
which average 21 m in height. The conductors are approximately 16 m
above the water at the Bybee Lake crossing. The horizontal distance
between the outermost conductors of the two transmission lines is about
22 m. The 115 kV line was energized in 1974.
Bybee Lake is utilized by waterfowl, shore and waterbirds, and
large numbers of gulls (primarily Glaucous-winged). The gulls and crows
are attracted to a sanitary landfill southwest of Bybee Lake. Waterfowl
hunters utilize the area and fishermen, bird watchers, and other recreationists
are present at various times.
58
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"PORTLAND, OR'EgGnI
-a Centerline of BPA 230kV line
D o Centerline of PGE 115kV line
• Dead Bird
k >\ 100 m
6/5.
6/6 j
N J
\f/
7/1,
BYBEE LAKE
BY BEE LAKE
7/3-
7/21
Sanitary Landfill
230kV Steel Tower
6!4m
6.4m
-z/49&m*v.
50m
(Awe.)
Figure 2. Approximate locations of 60 dead birds found near two
transmission lines in Oregon during periodic searches
from 29 January through 28 April 1977.
59
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Dead Bird Counts
Initially, 41 dead birds were found between towers 7/2 and 6/6. It
appeared the length of time the birds had been dead ranged from a few
days to about 2 months. Additional searches between towers 7/2 and 7/1
were made on 5, 16, 19, and 26 February; 5, 12, and 19 March; and 28
April 1977. The span between 7/1 and 6/6 was searched on all these days
except 16 February. The section between tower 6/6 and 6/5 was also
searched every day except 5 February. Searches were made between 7/3
and 7/2 only on 11 and 26 February.
Between 29 January and 28 April 1977, a total of 60 dead birds was
found during the searches (Table 2). Thirty percent of the birds had
externally noticeable collision-type damage such as broken wing bones
and lacerations about the head, neck, or breast. Twenty-one birds
eventually could not be relocated during the dead bird searches. Most
of these were probably removed by scavengers, although some may have
been missed by searchers. Other biases exist because an unknown number
of birds probably fell into Bybee Lake and were not found, and others
may have sustained mortal collision injuries but were able to hide or
move away from the right-of-way before they died. Anderson (1978)
estimated his dead bird count was about 58 percent of the actual mortality,
and the corresponding estimate reported by Scott et al. (1972) was about
20 percent.
Flight Counts
Observations of bird flights across the spans where the dead birds
were found were made on four occasions (Table 3). These, plus observations
made incidentally to conducting the dead bird searches, indicated that
the heaviest gull flights were during early morning when the birds flew
south across the line to Bybee Lake and the landfill and during evening
when they returned to their roosting sites to the north. Flights continued
across the spans in both directions throughout the day, however, at
reduced intensities. The gull population using the sanitary landfill
appeared to number several thousand birds. Other birds observed in
smaller numbers included ducks, crows, Great Blue Herons, shorebirds,
and passerines.
1 estimate that on the days counts were made, between 2,000 and
6,000 bird flights occurred across the 230 kV line between towers 7/3
and 6/5. Using a conservative estimate of 2,000 bird flights per day and
assuming similar flight intensities in late fall, at least 354,000 bird
flights occurred during the time (1 November 1976 to 28 April 1977) in
which the 60 birds were killed. Tripling this latter number of 180 to
allow for sample biases mentioned above indicates roughly 0.05 percent
of the estimated total flights resulted in fatal collisions.
My data suggest the actual percentage of flights resulting in fatal
collisions probably varied by species. However, because of the limited
amount of diurnal flight counts and a lack of data on nocturnal flights,
an estimate of such variations was not attempted. My overall estimate
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Table 2. Identification of dead birds found between towers 7/3 and 6/5
of the BPA Ross-St. Johns 230 kV transmission line from 29
January through 28 April 1977.
Species Number found
Gull
29
Green-winged Teal
7
Pintail
7
American Coot
3
Ruddy Duck
2
Western Sandpiper
2
Great Blue Heron
2
Common Crow
2
Mallard
1
Unidentifiable duck
1
Killdeer
1
Common Snipe
1
Mourning Dove
1
Song Sparrow
1
Total
60
61
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Table 3. Summary of counts of bird flights across the right-of-way of
the BPA Ross-St. Johns 230 kV transmission line where dead bird
counts were made.
Flight direction
Between line structures Total
each
7/3-7/2 7/2-7/1 7/1-6/6 6/6-6/5 direction
30 January 1977, 0700-0900
Northwest
Southeast
NL
N
82
547
31
75
N
N
113
622
19 February 1977, 0700-0900
Northwest
Southeast
54
478
80
253
47
51
83
68
264
850
26 February 1977, 1700-1730
Northwest
Southeast
133
4
259
11
34
2
134
5
560
22
5 March 1977, 1000-1100
Northwest
Southeast
37
306
14
29
22
8
380
143
453
486
Total
3,370
Approximately 77 percent of these flights were by gulls,
No counts made.
62
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is one order of magnitude smaller than that interpreted from the data
reported by Anderson (1978). Anderson's data indicate an average of
1,700 daily diurnal bird flights during the fall of 1974 when there were
an estimated 338 collision casualties. Depending on the extent of
nocturnal flights in Anderson's study area, the actual percentage of
collisions in his study may have been closer to the magnitude estimated
for Bybee Lake.
Bird Collisions
During the flight observations (tabulated in Table 3), a gull
collided with a 230 kV conductor. During incidental flight observations,
a shorebird collided with the overhead groundwire. Although the gull
fell to the ground and the shorebird fell into Bybee Lake, both were
subsequently able to fly away. The frequency of an observed collision
during periods of good visibility, one collision per 3,370 flights, is
in contrast to the corresponding ratio of one in 11,061 interpreted from
the data reported by Anderson (1978). Anderson reported this ratio as
one in 250,000; however, this was apparently based on two observed
collisions out of the 553,059 total flights observed at the slag pit.
Only 4 percent (22,122) of the birds actually flew across the transmission
lines, and I believe this latter number is the appropriate value to
relate to observed collisions.
Eighty-nine percent of the birds counted flew above the overhead
groundwire (or conductors in the span between 6/6 and 6/5 of the 230 kV
line with most birds just clearing the line. Nine percent of the birds
flew under the conductors of the 230 kV line, and only about 2 percent
flew between the upper and lowermost conductors. On 58 (1.7 percent)
occasions, birds were observed to turn back as they approached the line.
In most cases, after flying parallel to the line and gaining altitude,
the birds flew over the line.
The bird flight observations and the locations of the dead birds
suggest that of those birds which bore no apparent collision damage,
most were probably killed by colliding with the 230 kV line. I hypothe-
size that the birds were flying in a northerly direction with the wind
(prevailing wind direction was from the south during my visits to the
study area). The birds struck the line and momentum caused most of them
to fall north of the center of the right-of-way. Although the two
collisions described above occurred when visibility was good, reduced
visibility was probably a determining factor in the fatal collisions.
CIimatological data obtained from Portland International Airport (9.4 km
southeast of the study area) showed that between 1 November 1976 and 29
January 1977 fog occured on 21 days and heavy fog (visibility 0.4 km or
less) occurred on 44 days. Between 30 January and 28 April 1977 (during
which only 11 dead birds were found), fog was present on 16 days and
heavy fog on 12 days.
In addition to monthly differences in collision mortality, there
were large differences in the number of dead birds found in each of the
four spans of the 230 kV line (Figure 2). The heaviest mortality,
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including all 21 ducks listed in Table 2, occurred between towers 7/2
and 7/1. This is consistent with flight observations which showed
almost all duck flights were across this span. The limited amount of
data collected on bird flights, however, does not provide an adequate
basis for explaining differences in mortality among the spans. Related
factors which may have determined the incidence of collisions include
the proximity of the spans to the sanitary landfill and Bybee Lake and
the presence of the overhead groundwire.
With the large number of birds flying across the two transmission
lines and with the formidable array of wires perpendicular to a low-
altitude flyway, one might expect to find more dead birds than we did.
Most birds were able to avoid the lines even, perhaps, during night or
in time of poor visibility during the day. Through social interaction,
most gulls in the area had probably learned the location of the transmission
lines as they learned the location of the sanitary landfill. Other
resident birds also were probably quite aware of the location of the
lines, at least during times when visual cues were available. Low-level
corona noise from the 230 kV line was usually audible during my visits
to the area. It is possible that corona noise and electric and magnetic
fields may provide location information to flying birds during periods
of reduced visibility (Lee and Griffith 1978). Whether such information
is an aid to birds in avoiding collisions with transmission lines has
yet to be determined.
WICHE TRANSMISSION LINE BIRD STUDY
In October 1977, a 1-year study began which was designed to provide
additional quantitative data on the effects of BPA transmission lines on
bird flights and collisions. This study is being conducted by James R.
Meyer, an intern with the Western Interstate Commission for Higher
Education (WICHE). Most of the field data for the study will be obtained
in three geographic areas having two or three primary sample sites per
area. These areas have been selected to include a variety of environ-
mental and transmission line conditions so the factors which may determine
the kinds and magnitude of effects on birds can be studied.
All sample sites contain some form of water or wetland habitat.
This type of habitat frequently attracts large numbers of birds including
waterfowl. These areas and the birds inhabiting them usually have high
ecological and social values. This study is, therefore, designed to
look at "worst-case" situations. By taking this approach, if problem
areas exist, they would most likely occur in these situations. There-
fore, an estimate of the seriousness of the problem can be more reasonably
made.
Study Areas
Sample site one in th$ Portland-Longview study area is Bybee Lake,
described above. Site two is near Longview, Washington, where two 500
kV lines and two 230 kV lines cross the Columbia River. This site is
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used by small to moderate numbers of ducks, and smaller numbers of geese
and swans are present at various times. Some of the towers have red
aircraft warning lights. Waterfowl hunters use the area at times.
A second study area is the Willapa National Wildlife Refuge on the
Washington coast; the refuge contains a 115 kV wood pole transmission
line. The section of line to be studied is from U.S. Highway 101 to
near the Long Beach Substation. Two sites will be studied, each having
a different type of line construction. Most of the line crosses wetland
habitat, and it crosses the Bear River. Moderate to large numbers of
ducks and geese utilize the area. Some waterfowl nesting also occurs
during the spring. The refuge is open to waterfowl hunting on certain
days during the season.
The central Washington study area extends from near Ephrata, Wash-
ington, south to State Highway 7. Sample site number one in this area
is a Rocky Ford Creek, and BPA lines at this site include a 500 kV line
and two 230 kV lines. Site two is in the Frenchman Hills Wasteway Area
and includes only a 500 kV line. Site three is Lower Crab Creek and
also includes the 500 kV line. This part of Washington is utilized by
moderate to large numbers of ducks and geese during fall and spring
migration. Some waterfowl nesting also occurs. This is also an important
waterfowl hunting area, and both public and private shooting areas are
found near the 1ines.
Study Methods
Data collection consists of two primary activities; dead bird
counts and bird flight observations. Because few studies of this type
have been conducted, the development and evaluation of methods of data
collection and analysis are important parts of the study. Suitable
portions of right-of-way of the lines in the primary study areas are
periodically and systematically searched for dead birds. If the habitat
permits, the entire right-of-way including a strip of adjacent land
{approximately 45 m out from the right-of-way) is searched. Birds found
are examined for cause of death, and their location is mapped. During
each search, an effort is made to locate all birds previously found and
left onsite as well as to locate new birds. By tagging and leaving
birds on the site, information on removal and decomposition rates can be
obtained. To obtain information on recovery success, a sample of dead
birds is randomly planted at least once on each site immediately prior
to beginning regular searches for dead birds. The location and number
of birds planted are not known to the searcher.
For all sections of lines where dead bird searches are conducted,
periodic and systematic observations of birds flights are made. Infor-
mation obtained by these observations will provide a basis for interpreting
the mortality levels obtained with the dead bird counts. The following
information will be noted for all birds approaching the section of line
under observation: species or type of bird, number in flock, direction
and altitude of flight, and behavior when approaching the line. Most
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flight observations will be done during daylight including some counts
from daylight to dark. Beginning in January 1978, a night viewing
device ("Javelin" model 226) will be used for nocturnal flight observa-
tions and to observe the behavior of predators and scavengers. A 16 mm
movie camera will be used to document the various types of flight
behavior which are typically observed in each study area.
The feasibility of various methods to remotely monitor bird flight
behavior and collisions will be studied. These methods will include
time-lapse photography, closed circuit television, and devices which
monitor collision impacts with conductors or overhead groundwires.
Between 22 October 1977 and 28 January 1978, each of the three
study areas will be sampled during alternating 2-week periods. From
February through June 1978, observations will be concentrated primarily
in the Bybee Lake and Central Washington Study areas.
Preliminary Results
Data from the study are still being collected and analyzed, so only
preliminary information is available at this time. During the initial
dead bird counts between 22 October and 21 December 1977, a total of 19
birds was found in the three study areas along a total of about 5 km of
lines (James R. Meyer, personal communication). This number included
seven Green-winged Teal, two Red-winged Blackbirds, one American Robin,
two Mourning Doves, four Starlings, two Glaucous-winged Gulls, and one
Bufflehead. Ten of these were found in the Central Washington study
area near a 0.6 km long section of the 500 kV line at the Lower Crab Creek
site. All but five of the 19 birds found had collision-type damage
detectable by field examination.
During eight days of flight observations, Meyer saw five ducks and
three blackbirds collide with the overhead groundwire of the 500 kV
line. Five of the birds fell to the ground and at least two of these
received fatal injuries. The collisions occurred during good visibility.
During the time period in which the collisions were observed, 17,867
birds were counted flying across the line. These data show that, on the
average, there was one collision observed for every 2,233 flights counted.
This ratio is similar in magnitude to that described previously for the
230 kV line at Bybee Lake. The 500 kV conductors are 3.3 cm in diameter
and are in bundles of three for each phase of the delta configuration.
The two overhead groundwires are each 9.78 mm in diameter.
Exact flight counts have not yet been tabulated for the other
sites; however, waterfowl flight intensities at the Lower Crab Creek
site were the highest of any of the sites during the initial phase of
the study. By making flight observations during both day and night,
Meyer expects to express the collision mortality as a percentage of the
overall flight intensity and species composition. The final results of
the WICHE study may indicate the need for additional research including
the need to develop measures to mitigate adverse effects.
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DISCUSSION AND CONCLUSIONS
Experience with BPA transmission lines indicates such lines can
affect bird flights and that birds at times collide with conductors or
overhead groundwires. To date, however, I am not aware of situations
where BPA transmission lines represent a significant avian mortality
factor. Only preliminary data currently exists for basing such conclu-
sions, so any such conclusions must be considered tentative. Until more
definitive information is available, it seems reasonable to consider the
potential for bird strikes when evaluating the impacts of transmission
lines. This is especially so if areas utilized by threatened or endangered
birds may be affected. Even relatively small increases in mortality
from whatever source may be significant when these kinds of birds are
involved.
Based on studies of BPA lines and on my review of the literature on
bird collisions with power lines and other obstacles, it appears that
several factors need to be considered when predicting the effects of
existing or planned transmission lines on birds (Table 4). Currently,
information with which to evaluate the relative importance of these and
other factors in determining the incidence of bird collisions with
transmission lines is extremely limited. For example, little is known
about whether the structural and electrical differences between transmis-
sion lines and other types of utility lines also result in different
effects on birds. Therefore, I believe it is not desirable to attempt
to predict impacts of transmission lines on birds by using information
based only on observations of distribution or communication lines. It
Table 4. Factors which may determine the number of bird collisions
expected with a transmission line during some specific
period.
General category Factor Suspected high collision risk situations
Bird biology
Flight
Transmission line
Environment
Species
Age
Health
Migration
Sex
Flight Intensity
altitude of flights
Size of flocks
Time of flights
Tower type
Voltage
Conductor charac.
No. of lines
Overhead groundwire
Line length
Age of 11ne
Aircraft warning
light
Weather
Habitat
Human activity
Geographical
location
Nocturnal fliers or those with awkward flight characteristics
Imnature birds with limited flight experience
Sick or injured birds
Migrants as opposed to resident birds
Birds involved in nuptial displays
Large numbers of birds crossing the right-of-way during all times of day
Altitudes equal to or lower than the uppermost wires
Large flocks -with small spacing between birds
Nocturnal flights and diurnal flights during inclement weather
Guyed structures or tall towers near river crossings
Lower voltage lines with reduced electric field and corona effects
Small diameter, single conductor/phase configurations
Double-circuit lines with wire at different heights
Multiple wires small 1n diarreter compared with conductors
A long line through a high use area
A newly constructed Hne before birds can habituate
Nonflashing lights on towers in established flyways
Fog, snow, rain, sleet, or high winds
Attractive bird habitat on and surrounding the right-of-way
Hunting and other human activities which startle or distract birds
Lines located perpendicular to a narrow* low-altitude flyway
-------
may well be that the larger size of the transmission line conductors and
the electrical fields and noise which they produce combine to decrease
the potential for bird collisions - especially during the critical times
when visibility is poor. It also appears that the presence of one or
more small diameter overhead groundwire on a transmission line may
greatly increase the potential for bird collisions. For all studies and
reports involving transmission lines and birds, it is therefore, important
that details of the lines be given along with information on pertinent
environmental conditions. As a minimum, information should be given on
the number and voltage of all lines present and the size and number of
conductors and overhead groundwires. For all studies involving dead
bird counts, information on bird flight intensities, altitudes, timing,
and species composition during the time the mortality occurred should be
provided.
As a biologist, I am concerned with all sources of avian mortality.
As a biologist for a power marketing agency, I devote most of my research
efforts toward identifying the mortality associated with transmission
lines. I believe that collision mortality should be considered in
relation to other possible adverse effects of transmission lines (e.g.,
increased vulnerability of birds using towers to illegal shooters} and
to possible beneficial effects (e.g., use of towers by birds for perching
and nesting). Although there is a need for research on the effects of
transmission lines on birds, this need also applies to other types of
utility lines and perhaps even to other types of man-made structures.
For transmission lines, at least, a goal should be to develop models
with which to predict the impact of existing and proposed lines on birds
with some degree of confidence. This will require multidisciplinary
studies conducted in a variety of environmental settings which include
the various types and configurations of lines.
Research may reveal areas where significant mortality (whether
defined in a political or ecological context) is occurring as a result
of birds colliding with transmission lines. Likewise, in some areas,
transmission lines may affect local flight patterns. In the case of
waterfowl, effects on flight behavior may result in either increased or
decreased waterfowl mortality if waterfowl hunting success near the
lines is changed. Until information derived from sound research is
available, utilities may be reluctant to expend the effort and funds to
develop means to mitigate suspected adverse effects. Likewise, until
information is available on the effects of existing transmission lines
on birds, decision makers may be reluctant to commit financial resources
to minimize potential effects on birds when new transmission lines are
designed and located.
I wish to thank Anthony R. Morrell and Dennis B. Griffith for
assisting me in collecting field data during the study of the 230 kV
line at Bybee Lake and for reviewing an early draft of this paper. My
thanks also to Dr. T. Dan Bracken and James R. Meyer for their review of
a draft of this paper. Dr. Bracken also provided the calculated electric
field strengths cited in this paper. I appreciate the assistance of
James Meyer for providing me with preliminary results from his study.
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EVALUATION OF A PROPOSED TRANSMISSION LINE'S IMPACTS
ON WATERFOWL AND EAGLES
Roger L. Kroodsma
Environmental Sciences Division
Oak Ridge National Laboratory
INTRODUCTION
This paper summarizes an environmental assessment of the potential
impacts of a proposed transmission line on waterfowl and Bald Eagles.
This transmission line would be one of three 345 kV lines servicing the
nuclear powered Tyrone Energy Park (TEP), which is proposed by the
Northern States Power Company (NSP) to be constructed near Eau Claire,
Wisconsin. The line would cross the Mississippi River just north of Red
Wing, Minnesota, through important waterfowl and Bald Eagle habitat. The
U.S. Nuclear Regulatory Commission (NRC) has reviewed NSP's application
to construct TEP, has prepared a Final Environmental Statement (U.S. NRC
1977), and has completed public hearings. The Wisconsin Public Service
Commission is presently reviewing the TEP application.
As an ecologist, I was a reviewer for the NRC and prepared the
portions of the Environmental Statement dealing with impacts of trans-
mission lines. The purpose of this paper is to discuss potential impacts
of transmission lines on migratory waterfowl and eagles, to present the
TEP case as an example problem, and to suggest possible mitigation
techniques and needed research.
POTENTIAL IMPACTS
The potential impacts of transmission lines on both waterfowl and
Bald Eagles include mortality due to collisions (not electrocution) with
lines and towers, and disturbance of important habitat (e.g., eagle nest
sites, important waterfowl resting and feeding areas). Electrocution is
not considered a problem with high voltage transmission lines (in contrast
to the smaller distribution lines), because conductors are far enough
apart to prevent simultaneous contact of a bird's extremities with
adjacent conductors.
Waterfowl collisions with lines appear to be responsible for a very
small fraction of hunting and nonhunting mortality. Nationwide data
reported by Stout and Cornwell (1976) indicate that only about 0.07
percent of nonhunting mortality results from collisions with lines. This
figure includes data not only for transmission lines, but also for the
smaller distribution lines and telephone wires. Thus, deaths caused by
transmission lines would appear to have had no Significant impact on
waterfowl populations. As transmission lines proliferate, however,
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impacts will increase and become of more concern. Most collision mor-
tality probably occurs near breeding, feeding, or resting areas where
birds fly low. On long-distance migratory flights and flights between
feeding and resting areas, flocks generally fly high enough that collision
with lines is unlikely. As far as disturbance of waterfowl is concerned,
a few observers (no published accounts as far as I know) believe that
large transmission lines cause some avoidance of habitats within roughly
one quarter mile of the lines.
For eagles, collision with power lines would not seem to be a
problem, because the species has keen sight, flies relatively slowly,
and maneuvers well. However, if eagles often fly during poor visibility
(e.g., fog, dusk), collision potential is increased. Also, because of
their hunting behavior, eagles may not always be attentive of power
lines. Several papers (Beecham and Kochert 1975, Bel isle et al. 1972,
Coon et al. 1970, Cromartie et al. 1975, Mulhern et al. 1970) have
reported deaths of eagles due to collisions with power lines. The type
of line usually involved has apparently been distribution lines, with
which electrocution would also have been a possibility. Mortality data
for immature and adult bald eagles indicate that about 10 percent of the
known deaths from 1960 through 1972 resulted from impact injuries, many
of which resulted from collisions with power lines (Table 1). Authors
of these papers, however, stated in personal communications with me that
Table 1. Mortality of fledged Bald Eagles in the United States.
Source
1960-65d
Vears
1966-68b
1969-70°
1971-72d
Total
Percent
Shot
45
28
18
13
104
47
e
Unknown
18
20
3
4
45
20
f
Impact
7
10
4
1
22
10
Poisoning
1
1
7
14
23
10
Electrocution
1
2
2
1
6
3
Trapped
2
2
1
0
5
2
Miscellaneous
2
6
4
4
16
7
a Coon et al. 1970.
b Mulhern et al. 1970.
c Bel Isle et al. 1972.
d Cromartie et al. 1975.
e No diagnosis could be made on the basis of autopsy findings.
f Impact injuries resulted from the eagles strlJdng some object, frequently & power line or tower
(the sources gave no more breakdown for impact).
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electrocution may have, in fact, accounted for some, if not most, of
these "collision" deaths. Electrocution may have been mistakenly omitted
as the cause of death because of the lack of obvious electrocution
burns. Thus, it appears that collision with lines may not account for
as large a fraction of mortality as the literature reports. The effect
of disturbance caused by the presence of power lines in important hab-
itats would probably be more critical in breeding areas than in nonbreeding
areas. Assuming that eagle breeding activity is relatively susceptible
to disturbance, one might conclude that the proximity of transmission
lines would adversely affect eagle reproduction. However, many other
raptor species have been observed nesting in transmission line structures,
primarily where other suitable nest sites were not available. Raptors
in general seem to become accustomed to various man-made structures, and
their use of habitat may not be greatly disturbed by nearby transmission
lines. Nevertheless, effects on rare or endangered raptors, such as
eagles, should receive attention.
THE TYRONE ENERGY PARK CASE
One of the 345 kv lines of the TEP is proposed to run west from the
plant, cross the Mississippi River, and connect with the existing Prairie
Island Nuclear Station on the west bank of the river about five miles
north of Red Wing, Minnesota (Figure 1). This region of the Mississippi
River, like much of the river, is used by large numbers of migrating
waterfowl and Bald Eagles. An assessment of the potential impacts of a
power line crossing the Mississippi River in this area was needed for
the environmental impact statement. Initially, NSP proposed two possible
routes ("proposed" and "Lock and Dam", see below). One route passed near
a wetlands complex of about 1100 acres (Gantenbein Lake and associated
wetlands, see Figure 1) that is heavily used by migrating waterfowl,
while the other passed through the wetlands complex. The Gantenbein
wetlands constitute a private hunting preserve which is managed to
attract waterfowl, and in the hunting season it is hunted only every
other morning every other week. During the NRC review of the NSP
application, several other alternate routes were investigated by both
groups, as described below.
As seems to be the case in most environmental assessments, there
was less information available on which to assess the Impacts and_
identify the best route than an ecologist would like. Concentrations of
overwintering eagles had been observed at several sites along the Missis-
sippi River near Prairie Island, and the number of eagles in each area
had been estimated. Also, 15 or 20 eagles had occasionally been seen in
a forested area at dawn and dusk, indicating the birds roosted there.
However, the exact roost site had not been sought or located. Frequency
of migrating eagles in the area had not been documented. Eagles were
not known to inhabit the area during the late spring and summer. Numbers
of migratory waterfowl frequenting various wetland sites in the area had
not been documented. However, the number of each species passing through
the Mississippi Flyway in this region (Table 2) could be roughly esti-
mated from Bell rose (1976). A small fraction of this number of birds
would be expected to occur near Prairie Island. Persons familiar with
the area believed that much larger numbers of waterfowl frequented the
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u*. .
PRAIRIE ISLAND
Figure 1. Proposed and alternate routes crossing the Mississippi
River and leading to the existing Prairie Island Nuclear
Station. Solid lines show existing transmission lines.
Double-dash lines represent possible routes to Prairie
Island, including the proposed route at Sturgeon Lake,
the lock and dam route at Lock and Dam No. 3, the Trenton
route at Diamond Island, and the Red Wing route at
Fed Wing.
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Table 2. Estimated numbers of waterfowl passing through the
Minneapolis-Prairie Island-Red Wing region during
spring and fall (from Bell rose 1976).
Species Number Corridor Status3
Whistling Swan 30,000-60,000 1
Snow Goose 50,100-100,000 3 (fall)
0-1,000 0 (spring)
Canada Goose
small races 500-2,500 5
larger races 15,100-50,000 3
American Wigeon 201,000-400,000 2 (fall)
Gadwall 11,000-25,000 4
Green-winged Teal 2,000-25,000 5
Mallard 201,000-375,000 4
Black Duck 1,000-10,000 5
Pintail 10,000-75,000 5
Blue-winged Teal 501,000-750,000 1
Shoveler 2,000-15,000 5
Canvasback 51,000-100,000 1
Redhead 40,100-100,000 2
Ring-necked Duck 36,000-60,000 1
Greater Scaup 0-500 0
Lesser Scaup 76,000-250,000 2
Buffiehead 2,100-4,000 4
Common Goldeneye b
Hooded Merganser b
Red-breasted Merganser b
Common Merganser b
Ruddy Duck 30,100-60,000 1
Corridor status is the rank of the migratory corridor through the
Prairie Island region as compared with other corridors, according
to five categories of decreasing species abundance from one to five.
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Gantenbein wetlands than other wetlands in the area. In an attempt to
characterize waterfowl distribution in the area, NSP personnel prepared
a map of the region within which alternate routes were located. The map
was based on study of aerial photographs and showed locations of wet-
lands and forests. Also shown were major waterfowl use areas and local
flight lanes as determined from persons familiar with the area. Addi-
tionally, NSP personnel determined from aerial photos the height of
trees along various routes; this was done with the idea of routing the
lines at or below treetop height through or adjacent to forests so
waterfowl would pass over the structures and avoid collision.
Four routes across the Mississippi River were examined in detail.
Each route had advantages and disadvantages as described below, but no
route appeared obviously superior in terms of overall impact on wild-
life, vegetation, land use, and people.
PROPOSED ROUTE
The proposed route, passing west through the Mississippi Valley,
would first cross about 0.7 miles of bottomland forest interspersed with
wetlands. Here the line span would be reduced from the normal 1200
feet, to 500 feet to minimize the height of the lines and towers. The
towers would be only about 70 feet high (normally they would be 94 feet
or more), which approximates the height of the taller trees in the area.
To maximize the advantage of reduced line height, the lines would be
routed through or adjacent to forest wherever feasible rather than
through the middle of wetlands. The reason is that as waterfowl and
eagles fly over the forest, they would pass over and above the towers
and lines, thereby avoiding collision. Also, the line might be less of
a visible disturbance if it were in or adjacent to the forest. After
crossing this area, the line would cross the Mississippi River channel
(0.3 miles wide) to a narrow spit of forested land separating the channel
from Sturgeon Lake. The line would then cross Sturgeon Lake (0.4 miles
wide) to the west shore where the existing Prairie Island Plant is
located. This route is the only one that crosses a lake. Sturgeon Lake
is used considerably by diving waterfowl. Towers roughly 200 feet high
would be required on the east channel bank, on the spit, and on the west
shore of Sturgeon Lake. These tall towers and lines over open water
would be a collision hazard to both waterfowl and eagles. Just to the
south of this route are the Gantenbein wetlands, which are heavily used
by migrating waterfowl. Almost all of these wetlands lie more than one-
third of a mile from the proposed route; because of this distance a
power line through this route may have little impact on waterfowl use of
this area. However, major waterfowl flight lanes connecting with the
wetlands pass over this route. Therefore, collision with lines on the
proposed route is a potentially serious problem, unless flights are
usually high enough at this distance from the wetlands that collisions
are unlikely. In summary, the major disadvantages of this route are the
proximity to the high waterfowl use area and the crossing of Sturgeon
Lake. An advantage of the proposed route is that eagles do not frequently
use this particular area.
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LOCK AND DAM ALTERNATE
The lock and dam route passes near the center of the Gantenbein
wetlands. Therefore, it is considered an unacceptable route. The only
advantage of this route is that the lines would need to cross only the
river channel, and this crossing would be adjacent to a lock and dam
with some existing tall structures.
TRENTON ALTERNATE
The Trenton alternate would cross the Mississippi River below the
lock and dam and pass through much forested land in the Mississippi
Valley. The primary advantage of this route is that it is distant from
the high waterfowl use area. Also, much of the line could pass through
or adjacent to forest (using short spans as in the proposed route),
thereby reducing collision potential for waterfowl and eagles. The
major disadvantages are that the river crossing is located in a rela-
tively major eagle use area compared with other areas along the river,
and that evidence indicates there is an eagle roost somewhere in the
forest in this area. Wintering eagles are apparently attracted to this
area because the river remains open longer below the dam than at many
other areas.
RED WING ALTERNATE
The Red Wing alternate crosses the Mississippi River adjacent to
Red Wing, Minnesota. Its primary advantage would be little impact on
waterfowl. The line would pass primarily near areas of human disturbance
(residential, commercial, and industrial areas and corridors with
existing transmission lines) where waterfowl are relatively scarce.
Disadvantages are that the line would use more land with a relatively
high dollar value, would be near and visible from several residential
areas, would cross the Mississippi River in an area having a wintering
eagle concentration equal to that at the Trenton crossing, and would be
from three to five miles longer than the proposed route.
CONCLUSION
Selecting one of these four routes involves various tradeoffs:
waterfowl vs eagles, waterfowl vs people, and waterfowl vs economic
costs. The Trenton route might have minimal impact on waterfowl and
people but greater impact on eagles than the proposed route. If the
potential for eagle collisions with power lines is low enough to be of
little concern, the Trenton route might be the best. This potential,
however, is not well known. The NRC staff has concluded that no route
has obvious overall advantage in terms of wildlife, environment, aes-
thetics, and land use. This conclusion has been presented to the NRC
Atomic Safety and Licensing Board for Tyrone, which is an NRC decision
making body. As of this writing, the Board has not yet ruled on the
Tyrone application.
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RESEARCH NEEDS
For site-specific cases where a proposed line would pass near
important waterfowl or eagle habitats, the following information should
be obtained for use in route determination: local distribution, including
population estimates; flight patterns; and flight height. This infor-
mation should be provided by species, season of the year, and daytime
and nighttime periods, as appropriate.
In general, better knowledge of waterfowl and eagle behavior would
have helped this assessment of impact, route selection, and possible
mitigation. Knowledge of the height above treetops at which waterfowl
and eagles fly during short-distance flights would help determine the
value of reducing tower and line height and routing through or adjacent
to forest. Information is needed on the extent to which waterfowl and
eagles fly at low altitudes or fly to and from resting and feeding areas
during poor visibility (e.g., fog and darkness). Use of habitats near
lines should be studied to determine the degree to which lines disturb
waterfowl and eagles.
Also useful would be studies of mortality at existing lines; for a
waterfowl breeding population or migratory flock using a given area
containing a power line, the fraction lost due to collision should be
determined. Such a study would require both estimates of the number of
waterfowl susceptable to collision and the actual number that collide.
The number killed by a particular length of line is generally very
difficult to determine because of the difficulty of finding dead birds
in dense vegetation, predator removal of dead birds, and escape of
injured individuals that die later. Because of these difficulties,
accurate estimates would require intensive searches, possibly with the
use of trained dogs, and experiments to determine rates of predator
removal. Vibration detection devices should be investigated and developed
for use in detecting collisions of birds with power lines.
Finally, the effectiveness of mitigation techniques should be
investigated. Such techniques would include reducing line height and
routing through or adjacent to forest, using horizontal instead of
vertical configurations of conductors so that less vertical flying space
is occupied and conductors can more readily be seen by approaching
waterfowl, marking lines in various ways for better visibility, and
routing lines parallel to existing transmission lines and other structures.
ACKNOWLEDGMENT
Oak Ridge National Laboratory is operated by Union Carbide Corporation
for the U.S. Department of Energy. Research for this article was supported
by the U.S. Nuclear Regulatory Commission under Interagency Agreement
DOE 40-544-75.
I wish to thank R. B. Craig, L. D. Voorhees, and E. G. Struxness
for providing helpful comments on the manuscript.
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TRANSMISSION LINE ENGINEERING AND ITS RELATIONSHIP
TO MIGRATORY BIRDS
W. Allen Miller
Tennessee Valley Authority
INTRODUCTION
In addition to its charge to provide electric power for the Tennessee
Valley region, the Tennessee Valley Authority (TVA) has a broad commitment
to coordinated resource development. While some of TVA's programs
actively promote migratory bird 1 ife—particularly waterfowl—TVA's
power transmission system probably has the potential, in some places, to
harm birds. Although there have been no reports of significant collision-
related bird mortalities in the TVA service region, TVA has attempted to
address the potential for bird collisions in a positive manner, prevent-
ing the problem or mitigating its seriousness, primarily by balanced
location of transmission routes. No extensive research programs have
been undertaken within TVA as of the date of this conference to attempt
an assessment of the causes and extent of any bird deaths.
This paper will not be an attempt to provide pat answers to the
questions before this conference. Its purpose is to introduce to the
conference some of the procedures and constraints controlling the devel-
opment of TVA's transmission lines and TVA's attitudes and efforts with
respect to resident and migratory birds. This discussion will identify
meaningful areas of flexibility in transmission engineering. If this
conference concludes that a problem exists with respect to birds colliding
with transmission lines, these will likely be some of the areas in which
the solutions will be sought.
Transmission engineering is a multifaceted operation encompassing
network load flow analysis, system planning, facility location, design,
construction, and operation. The only two distinct transmission engine-
ering operations which could have an influence on the potential for bird
collisions are transmission route selection and transmission line design.
TRANSMISSION ROUTE SELECTION
The route selection process begins with identifying the need for a
transmission line. Each transmission line is designed to meet a specific
need. Some lines are built to transfer fixed levels of power from point
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to point. Some are dedicated to serve variable loads. Others may be
built entirely to reinforce the transmission network or provide inter-
connections with other power systems.
There is a great deal of variety in the degree to which the terminal
ends of needed transmission lines are geographically established. Some
conditions may permit considerable flexibility in the choices of potential
transmission routes, while other lines may be narrowly constrained.
In a broad sense, the costs of alternative routes help to define
the study area. Good planning will eliminate unnecessary distance,
minimize the use of expensive angle structures, and avoid land where
social costs would be excessively high. These cost considerations,
however, are not the only criteria used to select transmission line
routes. Economic considerations are balanced against the extremely
weighty environmental considerations—among them, habitats and flyways
of migratory birds. Significant environmental issues which can be quan-
tified might dictate, for example, that a route simply bypass a critical
location, despite increased construction costs. The principal efforts
in route planning are to eliminate or diminish possible land use and
visual conflicts, avoid sensitive natural areas, and yet remain responsive
to the engineering costs and requirements of the job.
The methods used to identify and evaluate alternative transmission
routes involve field reconnaissance, mapping procedures, and consultation
and coordination with public representatives. Natural and man-made
features in the study area are examined and analyzed for relationships
to transmission line location. Information is gathered from various
sources within TVA; municipal officials; Federal, State, and regional
agencies; and from any other sources available. U.S. Geological Survey
7.5-minute series topographic maps are commonly used as a base to organize
geographically referenced data for display and analysis. Tentative
routes which generally best avoid conflicts are then selected. These
tentative routes are often modified and refined by field surveys which
identify smaller scale conflicts.
The process of selecting a proposed route is one of adjustment,
accommodation, and "fitting-in", and in this process the early iden-
tification of potential conflicts is paramount. Land use conflicts are
a prime consideration in transmission line location. Heavily urbanized
areas and areas of dense residential development obviously pose the most
immediate land use conflicts. New TVA transmission lines located through
these areas have a high priority placed on the use of existing utility
corridors and the reduction of visual impacts. Undeveloped industrial
sites, the value of which often lies in the unencumbered state of large
parcels of land, are often avoided as well, when site development cannot
be ascertained.
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In areas where unique wildlife or plant habitats might be harmed by
construction activities or the continued presence of a line or right-of-
way, routes are generally chosen to avoid the more sensitive locations.
Care is taken to review projects against cataloged information systems
operated by the various State and Federal agencies, and the routes are
closely reviewed by TVA staff biologists, historians, and archaeologists.
The Tennessee Valley region is liberally endowed with parks, rec-
reation areas, and wildlife management areas. It is essentially impossible
for an agency assigned the responsibility of serving area electric needs
to state categorically that it will completely avoid these areas. TVA's
record shows that a reasonable effort has been made to avoid these
areas, and where it was impossible to avoid them, TVA has worked with
any other parties involved to create the least possible environmental
impact.
TRANSMISSION LINE LOCATION EXAMPLE
This location example will serve to illustrate TVA's efforts to
minimize conflicts and impacts in potentially sensitive areas and show
how these unavoidable situations can occur. This example involves a
proposed transmission line to supply power to an industrial plant at
Decatur, Alabama in 1974 (Figure !}.
The situation, very briefly, was this: The city of Decatur had
developed along the south shore of Wheeler Lake. On the north side of
the reservoir is a small airport in an area of prime industrial and
commercial development potential; this area was mostly open farmland at
the time of the study. Between the city and this developing area, along
the north shore of the lake, is a wooded green belt approximately 1 mile
in width and projecting for a way up some of the inlet creeks. This
green belt consists of the Wheeler National Wildlife Refuge and the Swan
Creek Wildlife Management Area, together totaling over 37,000 acres.
General Motors was locating a new plant in this industrializing
area near the airport. The transmission line to supply power to the
plant lay 4 miles away across two major four-lane highways and a rail-
road. The plant operations required a high degree of reliability of
electric power supply. For this reason a loop 1ine--actually two lines-
was required so the plant could eventually be supplied power from either
direction on the existing 161 kV transmission lines. The power require-
ments of the plant were phased so that only one line was required initially.
That is the essence of the situation. The primary factors influ-
encing the location of a 161 kV loop line to General Motors were:
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SCALE
GENERAL
MOTORS
L PLANT
| SITE
!K WltOU«
Smt AHA
INDUSTRIAL AND COMMERCIAL
/ GROWTH POTENTIAL
*H»AJOR
fATIRFOWl
AREA
WHEELER NATIONAL ^ILDLIFE
REFUGE \
Figure 1. Route location example: Huntsvi1le-Decatur, Alabama
161 kV transmission line loop to General Motors.
UJ
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1. Airport. The line had to be kept far enough away so that it
would not encumber the airspace and emergency glide paths.
2. Development potential. Most of the open land near the high-
ways and airport had been designated by local planning authorities
for industrial and commercial development. The value of these
properties lay in the unencumbered state of these large expanses
of land. The spatial arrangements of future plants or shopping
centers were unpredictable, and it was impossible to guarantee
in advance there would be no conflicts. Some development had
already occurred, and functional conflicts with these had to
be avoided as well.
3. Visual considerations. The highways indicated are main en-
trances to Decatur, so it was important to avoid deterioration
of the view. The generally flat, open land contributes to
long vistas.
4. Wildlife refuges. The management of these refuges naturally
is disturbed by any potential encroachments on the areas.
Management personnel were concerned with the reduction of
habitat and the possibility that birds might die from collisions
with the lines.
Constraints were thus identified for practically the entire study
area. There was no neutral ground where a transmission line could be
built without some conflict. The only course left was to work out a
location with full knowledge of the situation and full participation of
those affected.
In this instance, avoiding encumbrances on the developable land and
maintaining an adequate distance from the airport runways mandated a
location near the green belt. Once there, the location had to be
reconciled, to the extent possible, with the remaining constraints:
visual considerations and the wildlife refuges.
From a visual design standpoint, the edge between landscape features
is often the most acceptable location for a transmission line. In this
case, the margin between the open farmland the wooded wildlife areas was
the strongest permanent edge. The irregular woods margin could not be
followed precisely. Instead, the route was set back into the projecting
wooded areas both to straighten the lines and to gain a degree of con-
cealment from the highway vantage points.
By staying at the edges of the wildlife area and against or among
the trees as much as possible, instead of out in the open, three things
were accomplished: (1) the largest possible parcels of wildlife refuge
were left undisturbed, (2) crossing a major waterfowl feeding area was
avoided, and (3) there was an attempt to keep the wood poles and con-
ductors from presenting unpredictable obstacles to birds in flight.
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The precise location of the line was worked out in close, on-the-
ground cooperation with the U.S. Fish and Wildlife Service and the
Alabama Game and Fish Commission. These people then monitored the
survey and construction activities on the line as it was built. At the
end of the process the rights-of-way through the wildlife areas were
revegetated with wildlife food seed mixtures preferred by the U.S. Fish
and Wildlife Service.
An attempt was made in the design of the transmission line to take
into account the issue of bird collisions. The single wood pole con-
struction used for the General Motors line permitted a greater degree of
location flexibility than steel tower construction. Wood pole lines
presented a profile on the same order of height as the adjacent forest.
By maintaining a low profile, by staying either against or amidst the
wooded areas and avoiding primary feeding concentrations, and by de-
signing the lines so the poles of the parallel lines would be side by
side as much as possible, the location participants believed the poten-
tial for bird collisions with the transmission lines was minimized.
The use of wood poles also helped reduce the additional cost in-
curred by approximately 2 miles of extra line.
TRANSMISSION LINE DESIGN CONSTRAINTS
The design of transmission lines is inherently not very flexible.
The physical characteristics of power lines are determined for the most
part by engineering performance, reliability, public safety, and economics.
This leaves little opportunity for design compromises to reduce bird
collision potential. Electrical performance characteristics determine
wire sizes, spacing, configurations, and number of circuits. These
characteristics combine with economics, topography, climate, strength of
materials, and many other factors to form the constraints which guide
transmission engineering. Let me briefly discuss some of these con-
straints on line design and point out areas where some flexibility
exists.
Except in localized situations, our society is basically dependent
upon transmission lines to deliver electric energy from remote generating
sources. Transmission facilities also tie adjacent electric power
systems together so that generating capacity at various locations can be
made available to the demand on any one system. For technological and
related economic reasons, almost all such electric power in this country
is transmitted on overhead three-phase, alternating current lines. Each
one of the phase conductors must be kept separated.
ELECTRICAL INSULATION
Except at supporting tower locations, insulation for these conduc-
tors is the air around them. The clearances between overhead transmission
lines and nearby objects are set primarily to avoid the possibility of
flashover. The flashover distance—the distance an arc will jump
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and short out the circuit—varies with the voltage rating of the circuit
but is well within the prescribed design distances. Conductors on a TVA
500 kV transmission line, for example, have a phase-to-tower clearance
of 12 feet. That is, the nearest grounded object (including the support-
ing tower and shield wires) must be at least that far away from the
conductor. The individual phases must be spaced at least 30 feet apart.
LIGHTNING PROTECTION
Lightning storm activity in most parts of the country presents a
real hazard to power line reliability through direct lightning strikes
which can cause power outages by flashing over insulators. In some
cases lightning can seriously damage insulators and/or sections of wire.
To provide protection against lightning, a smaller shield wire is placed
above the phase conductors to intercept the strikes. This wire (or
wires) in effect provides a "tent" of protection for the line. This
electrical shadow concept is considered in most cases to extend pro-
tection at an angle of 30 degrees from vertical. The coverage in re-
lation to the conductors and other surrounding influences determines the
number and placement of these shield wires.
WIND PRESSURE EFFECTS
Wind pressure can cause conductors to swing. In the free spans
between towers and under some wind conditions, the possibility exists
that individual conductors will swing "out of phase," so to speak, and
move toward each other. Therefore, the conductors have to be spaced far
enough apart at the towers to control the unrestrained midspan phase-to-
phase distance. For a 500 kV power line with horizontally spaced conductors
restrained at each structure, the distance from one phase to the next is
30 feet. Side swing also has a direct bearing on the width of rights-
of-way and on the separation between parallel power lines.
CONDUCTOR HEIGHT RELATIVE TO GROUND
The height of a conductor at any given location depends upon (1)
minimum safety codes based on the flashover distance for a particular
operating voltage, (2) topography under the line and objects that can
intrude into the free space, (3) climatic factors and power flows that
influence conductor sag, (4) electric field effects, and (5) spacing
between towers along the transmission line.
Conductor heights above ground are set primarily by the electrical
flashover distance in air which varies with the line operating voltage
level. This flashover distance must be set liberally because of the
many changes that can occur for a variety of reasons in the free airspace.
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Air pressure, temperature, humidity, and airborne particles can alter
the insulating value of air. People, animals, and mobile objects
frequently occupy space under the line. Trees and fast growing shrubs
can, in a short period, significantly reduce conductor clearances.
Electrostatic fields, which are most noticeable in the extra high
voltage range, introduce another design parameter to be considered in
selecting minimum conductor heights. By maintaining adequate conductor
heights, the ground level strength of these fields can be controlled to
avoid excessive induced voltages, currents, or other undesirable effects.
Conductor heights are not uniform along the length of a line.
Conductors, supported between towers, sag under their own weight along
catenary curves. Naturally, in hot weather or when conductor tempera-
tures are increased by heat from resistance, the conductors will sag
even lower than normal. Conversely, under low ambient temperatures the
conductors will stretch tighter and higher. All points along these
catenary curves must maintain at least the regulated minimum height
regardless of operating temperatures or topographical extremes.
STRUCTURE SPACING
Although structure spacing is by no means a random process, it does
represent one of the more flexible areas of transmission engineering.
Tower spacing is heavily dependent on topography with the design attempt
made to locate towers along the rights-of-way where the greatest design
and cost advantages can be realized. The optimum tower locations,
however, often must be compromised to avoid or minimize land use con-
flicts. A variety of spacing and structure height combinations can be
used to maintain minimum ground clearances. A great many closely spaced,
low structures can accomplish essentially the same task as fewer tall
structures with long spans.
The types of structures used.for a line also influence the spacing
of structures. Shorter spans in the range of 400 to 600 feet are char-
acteristic of wood pole construction, while spans may range from 700 to
1400 feet for steel construction. The height and strength limitations
on wood structures are the basic reasons for their shorter span capabilities.
STRUCTURE STRENGTH
The reliability of transmission support structures is a vital link
in the reliability of the transmission system. Transmission structures
must be able to withstand tremendous forces. They must bear the weight
and stabilize the placement of the conductors, insulator strings, and
grogndwires not only under normal circumstances but under the most
extreme conditions predictable for the location. Ice and wind loads on
the conductors and on the towers themselves can more than double normal
loads.
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Because of the side loads on structures at transmission line angle
points, the support structures must be much stronger (and more expensive)
than the straight-1ine tangent towers. Multi-circuit transmission
towers have much greater loads to support than do single-circuit towers.
Although transmission lines are built so that loads are normally static,
the towers are designed so that even if one conductor were to break, the
dynamic forces resulting will not destroy the tower or the remaining
conductors.
STRUCTURE SELECTION
Within these parameters there is enough design latitude to allow
many different tower styles and configurations. The variety of aesthetic
structures available attests to that. Hot all of the tower designs
available, however, are suitable for general use in a transmission
system. Many of the aesthetic structures are limited in their loading
capacities so that their potential usefulness is reduced. Other practical,
economic, and environmental factors must also be considered in selecting
structure types.
Because of the number of towers used, the cost of each must be kept
as low as possible. It must also be possible to construct towers in the
nearly impossible places transmission lines sometimes must cross. The
traditional self-supporting, laced-steel structures meet these requirements.
They provide the flexibility in design to assemble a very strong structure
from lightweight, relatively inexpensive parts. The self-supporting
feature eliminates the additional encumbrance of the right-of-way which
a guyed structure would cause. In construction, these lightweight parts
provide a bonus in reduced impacts and costs of hauling heavy structures
over the rights-of-way. Except at sharp angles (over 20 degrees)„ these
towers normally do not require concrete foundations - a major cost and
construction impact savings.
CONCLUSION
The purpose of this discussion of transmission engineering is to
identify the reasonable—and unreasonable—avenues of pursuit for attempts
to adapt transmission lines to reduce or avoid bird collisions. These
areas of flexibility may be summarized briefly:
1. Attempts can be made to identify significant problem areas in
advance so they can be avoided when possible by sensitive
route selection.
2. Often some transmission line design flexibility exists in the
choice of support structure heights and spacing.
3. There is a degree of latitude in the choice of support structure
materials and configurations.
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It bears emphasizing that these areas of flexibility do not indicate
randomness in transmission engineering. These areas still are bound by
strict engineering constraints and guided by economic responsibilities.
Although bird collisions with transmission lines have not become a
significant issue in the TVA region, it is recognized that some bird
collisions occur. In study areas where line locations might raise the
likelihood of bird mortalities—whether through habitat alteration or
collision potential—then the transmission line engineering processes
attempt to take this into account and work to minimize damaging effects.
In the near absence of research-influenced and cost-effective design
measures to reduce bird collisions, TVA's efforts to mitigate collision
impacts currently rely heavily on sensitive route selection.
ACKNOWLEDGMENT
Support from the personnel of the Division of Transmission Planning
and Engineering, Tennessee Valley Authority, is gratefully acknowledged.
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routing transmission lines through water bird
HABITAT IN CALIFORNIA
Edward W. Col son
and
Ellen H. Yeoman
Pacific Gas and Electric Company
INTRODUCTION
Pacific Gas and Electric Company (PGandE) first became involved in
bird/power line interactions in 1970. At that time, concern was raised
about the ecological impact of electric power transmission lines and
their supporting steel towers on wildlife within the South San Francisco
Bay of California. Mr. Philip Arend of Wildlife Associates, Inc., was
consulted to evaluate the effects of existing power lines in the bay and
to offer his professional opinion of the impacts these facilities pose
for wildlife. (Mr. Arend, formerly a waterfowl biologist with the
California Department of Fish and Game, has over 40 year's experience
working with waterfowl and marsh management.) His report was based on a
comprehensive literature review, interviews with numerous wildlife
refuge managers and other field workers, and personal observations over
a 3-month period. On the basis of this study, Mr. Arend concluded,
"Electric power transmission lines mounted on steel towers cause very
minor avian loss, and their adverse ecological impact on avian popula-
tions is negligible." Mr. Arend cited several instances of bird mortality
in water bird habitat mostly attributed to small diameter distribution
lines, not high voltage, large diameter transmission lines. In most
reported cases, adverse weather or human disturbance may have contributed
to the mortality incident.
Since 1970, PGandE has prepared many environmental impact reports,
and discussions of bird/power line interactions are included as appro-
priate. Specific studies to determine the scope of bird/power line
interactions in northern California have not been conducted because our
company was not convinced bird/power line interactions were significant
or because most projects did not enter water bird concentration areas.
Recently, PGandE has considered major transmission line projects
through water bird habitat in three separate areas in California: the
South San Francisco Bay, the Sacramento Valley, and the San Joaquin
Valley. These areas all contain important waterfowl wintering areas
within the Pacific Flyway. According to the U.S. Fish and Wildlife
Service, 60 percent of the migratory waterfowl on the Pacific Flyway
(approximately 4 million ducks and 700,000 geese) winter in California.
Large numbers of shorebirds also winter in the state. Concern for bird/
power line interactions has been raised locally by the California
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Department of Fish arid Game, the U.S. Fish and Wildlife Service, the
California Energy Resources Conservation and Development Commission, and
various public interest groups. We will briefly summarize these project
concerns.
STANISLAUS NUCLEAR POWER PLANT PROJECT
This project involves three possible power plant sites* and several
related alternative 500 kV transmission line corridors within California's
San Joaquin Valley. Important water bird habitat exists in many areas
of the valley, and it is virtually impossible to avoid crossing wetland
habitat with all transmission line corridors. While one corridor was
adjusted to avoid the Kesterson National Wildlife Refuge, another 4-mile
wide corridor incorporates part of the Grasslands Water District. This
area, in private ownership, receives Federal assistance for maintaining
wintering waterfowl habitat. The Grasslands Water District and California
Department of Fish and Game oppose transmission lines through the area
because they believe waterfowl will avoid habitat near power lines. Thus
waterfowl usage of the area will be reduced so that fewer birds would be
available for hunting. A reduction in waterfowl harvest would reduce
revenues and could force landowners to alter their land management
practices and possibly convert the wetlands to other uses.
SAM FRANCISCO BAY AREA COMBINED CYCLE PROJECT
This project includes four possible power plant sites and several
alternative 230 kV transmission line corridors within the vicinity of
San Francisco Bay. One of the proposed sites, North San Jose, includes
a preferred alternative transmission line route adjacent to the South
San Francisco Bay National Wildlife Refuge. The refuge serves an estimated
360,000 wintering waterfowl and 740,000 shorebirds. In addition, there
are numerous existing transmission lines crossing the bay in all directions.
Although PGandE proposed an alternative corridor adjacent to an existing
transmission line outside the refuge boundary, the U.S. Fish and Wildlife
Service and the California Energy Resources Conservation and Development
Commission have recommended additional studies of water bird flight
patterns and underground!ng alternatives before a final transmission
line corridor is selected.
*According to California Energy Resources Conservation and Development
Commission (ERCDC), utility companies are required to submit development
plans on a minimum of three proposed power plant sites. The ERCDC -
through a 36-month process of reports, workshops, and hearings - may
issue a decision to construct on one site and may offer one (or more)
land banked alternative.
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COAL POWER PLANTS
This project consists of studies of four possible power plant sites
and several alternative 500 kV transmission line corridors in the Sacramento
Valley. Several of the proposed corridors traverse water bird habitat,
including freshwater marsh and rice fields. The Sacramento Valley
supports an estimated 2 to 3 million wintering waterfowl and thousands
of shorebirds. The U.S. Fish and Wildlife Service has expressed concern
that bird/power line interactions, similar to what Dr. Willard, in the
keynote address, has described for the Klamath Basin, are possible. The
presence of existing power lines, dense tule fog, and high concentrations
of water birds provide conditions for possible bird/power line interaction
studies.
We have only briefly discussed these examples of potential bird/power
line interactions. It is important to point out that the three projects
differ considerably.
TRANSMISSION LINE ROUTING PROCEDURE
PGandE has developed a sound transmission line routing procedure
that addresses engineering, economic, and environmental concerns. The
possibility of bird/power line interactions is included in all planned
transmission line projects. The first step in the routing process is to
locate a study area, usually encompassing several potential power plant
sites and desired alternative power delivery points. The next step is
to select alternative straight-line corridors (usually 4 miles wide)
between the power plant sites and the designated delivery points. All
existing transmission line corridors are mapped and examined, and,
whenever possible, proposed corridors are modified to parallel existing
routes. A regional study is conducted to identify major constraints to
transmission line development. Environmental considerations at this
phase of the process include wildlife refuges, national and State parks,
natural areas, and other officially dedicated lands that may be affected
by the presence of transmission lines. Corridors are adjusted, where
possible, to avoid these designated areas. Adjustments based on con-
tinuing economic and engineering studies and land use may also lead to
changes in the corridors. Each corridor must contain at least one
feasible transmission line route.
The next step in the routing process is to choose potential trans-
mission line routes within the 4-mile wide corridors. Here, specific
resource elements that could be adversely impacted by transmission line
development are identified and, in most cases, avoided. Examples include
heron rookeries, eagle nests, and rare or endangered plant locations.
Eventually, an acceptable transmission line route is chosen through the
corridor.
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The ecological studies for transmission line routing involve
literature reviews, agency and public interest group input, field
studies, and report preparation. Studies on large projects may take
from 1 to 3 years to complete. Routing transmission lines in California,
as in many other parts of the Nation, is a difficult and complex task.
Many issues and concerns develop regardless of the process used to
locate a power line. Within the PGandE service area, the concern with
bird/power line interactions is another factor that is evaluated for all
new power line construction projects.
SUMMARY
The concern that transmission lines may pose a threat to some avian
species has been raised periodically in California since 1970. However,
until recently little data existed to indicate that bird/power line
interactions were worthy of specific study. The utility industry has
spent millions of dollars in research to address such concerns as thermal
effects on aquatic life, cooling tower drift effects, stack emission
effects, noise effects, and electromagnetic effects; and, until recently,
the concern with bird/power line interactions simply was not being
addressed. Even now, with an estimated 100,000 circuit miles of trans-
mission lines located in all representative habitats across the nation
and with millions of resident and migratory birds, incidents of bird
losses have seldom been reported.
The study of bird/power line interactions is warranted to place
these interactions in perspective. This will require sound research,
time, and money. To explore the possible scope of this concern, we will
be seeking information on collision potential, noise effects, electro-
magnetic effects, and avoidance of habitat.
A cooperative research approach should be our goal, with industry
and the State and Federal conservation agencies working together to
develop a predictive model to help us avoid areas of potentially signif-
icant impact and possibly to predict the consequences of locating a
power line in a given area. We believe the industry is now willing to
accept this opportunity and challenge.
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THE KLAMATH BASIN CASE
Ira D. Luman
Bureau of Land Management
Portland, Oregon
INTRODUCTION
This paper concerns a proposal by the Pacific Power and Light
Company to cross a highly important waterfowl concentration area in the
Klamath Basin, Oregon with a 500 kV power line - part of a proposed line
from Midpoint, Idaho to Medford, Oregon.
All data presented in this report are either directly quoted, or
summarized, from the "Final Environmental Statement, Pacific Power &
Light Company, Proposed 500 kV Power Line, Midpoint, Idaho to Medford,
Oregon", by U.S. Department of the Interior, Bureau of Land Management.
The author of this paper was part of that environmental impact statement
team.
In order to present background information, a short resume of the
proposed project and applicant's proposed route will be presented. If
more information is desired, please refer to the impact statement {USDI,
BLM 1977).
BACKGROUND AND HISTORY
Pacific Power & Light Company is in the process of constructing
generating facilities in Wyoming to utilize its strippable, low-sulfur
coal in that State. These facilities, Jim Bridger and Wyodak, with
existing generating facilities would provide electric generation in
excess of Pacific Power's Wyoming load requirements for the immediate
future.
To utilize the large quantities of excess Wyoming power, Pacific
Power proposes to transmit it to load centers in the Pacific Northwest,
southwestern Oregon in particular. To transmit this power from Wyoming
to the Northwest, Pacific Power proposes to construct a new 500 kV power
line between the Midpoint, Idaho substation and a proposed substation
near Medford, Oregon. To implement this proposal, Pacific Power filed
two applications with the Bureau of Land Management, U.S. Department of
the Interior, for a 175-foot wide right-of-way between Midpoint and
Medford, a distance of approximately 480 miles (Figure 1).
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Figure 1. Proposed power line route, Midpoint to Medford.
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According to Pacific Power the proposed transmission line will
serve the following purposes:
1. Provide a means of transferring surplus electrical energy from
Wyoming coal-fired thermal plants to load centers in the
Pacific Northwest.
2. Provide a direct means of supplying power to meet the energy
growth needs of southern Oregon.
3. Be available for back-up transmission capacity from the
Pacific Northwest to the Rocky Mountain area in emergency
situations.
4. Contribute to the reliability of the interconnected trans-
mission grid in the Pacific Northwest.
The proposed route passes over several areas important to waterfowl
for migration, resting, breeding, feeding, and wintering. Some examples
along the route follow (Figure 2).
The Bruneau Valley and adjacent Strike Reservoir in Idaho are used
by thousands of waterfowl. Major waterfowl concentrations occur along
the Snake and Bruneau Rivers and Klamath and Warner Valley Lakes. These
waters serve as habitat for resident species as well as provide food and
resting areas for the many migrants moving north and south east of the
Cascade Mountains.
The Warner Valley Lakes are a major nesting and feeding area in the
Pacific Flyway and support the greatest seasonal bird use of any area
along the proposed Midpoint to Mai in right-of-way. This area is also an
important rookery for herons and cormorants. Some 200,000 migrating
birds are believed to pass through the Warner Valley area annually.
Pelican Lake and Crump Lake, just south of the area that would be
crossed by the proposed right-of-way, contain one of the two White
Pelican rookeries in Oregon. The valley is an important migration
flyway for ducks, geese, swan, Sandhill Cranes, and many other waterfowl
and marsh birds.
South of Klamath Falls, Oregon, the proposed right-of-way would
cross the Klamath Basin, site of one of the world's greatest waterfowl
concentrations. The combination of proximity to open water, marshlands,
grainfields, and Federal and State refuges makes the basin a waterfowl
habitat that is unexcelled. The route would skirt part of the Klamath
Basin National Wildlife Refuge (Figure 3).
These, and adjacent farmlands, are part of an extremely productive
waterfowl area and flyway route. The refuges list over 180 species of
birds nesting in the basin. All of the common dabbling and diving ducks
are abundant, with Pintails predominating. White-fronted, Snow, and
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VO
-C*
Figure 2. Major flyways in relation to the proposed transmission line. &Ffe3i 975^'andr"wOa"eCrt8oPwl0, F'shenes
Tomorrow," USDI, 1965)
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•JD
cn
///J GRAINRELDS,
d SOMETIMES FLOODED
MARSHES
Proposed Route
MALIN SUBSTATION
Rgure 3. Klamath Basin with proposed route.
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Canada Geese are also present. The Ross's Goose, smallest of all North
American geese, passes through the Klamath Basin on its annual migration,
and according to the U.S. Fish and Wildlife Service, this flight repre-
sents the world population of this species. In addition to over 5
million waterfowl, thousands of grebes, White Pelicans, cormorants,
gulls, and terns migrate through the Klamath Basin annually.
A notable phenomenon in the Klamath Basin is the mass waterfowl
feeding flights which are local in nature and relatively low in altitude.
Within the Klamath Basin, by far the largest and most important of these
is the Lower Klamath feeding flight that at least once in each 24-hour
period traverses the flight corridor between the Lower Klamath Wildlife
Refuge portion (almost all of which is located in California) of the
Klamath Basin National Wildlife Refuges and the agricultural grainfields
which lie in southern Oregon, some 5 to 7 miles north of the Lower
Klamath Refuge. The bulk of this flight originates in the Lower Klamath
Wildlife Refuge (the resting area) and terminates in the grainfields to
the north (the feeding area), south of Midland and north of Township
Road, principally in the area known as Tulana Farms. A return flight to
the refuge is usually made within 12 hours of the initial flight.
According to Tom Roster, an instructor at the Oregon Technical
Institute and shotgun ballistician who has studied the local feeding
flights extensively, the Lower Klamath feeding flight numbers from a
minimum of 30,000 waterfowl to a maximum of 800,000 waterfowl. These
birds travel the feeding flight route at least once each day. (This
feeding flight phenomenon should not be confused with the reference to
over 5 million waterfowl that pass through the Klamath Basin at the peak
of each fall migration).
The area is heavily hunted. The Oregon Department of Fish and
Wildlife estimates more than 83,000 ducks, geese, and coots were har-
vested in the Klamath area in 1973. Several private gun clubs are
located near the Worden area. The Oregon Wildlife Commission operates
the Klamath Wildlife Management Area north of Worden for waterfowl and
upland game use. South of Worden are three U.S. Fish and Wildlife
Service Klamath Basin National Wildlife Refuges. These refuges contain
approximately 116,400 acres along both sides of the California-Oregon
border. The Lower Klamath Refuge lies 1 mile south of the proposed
right-of-way. The area is mainly flat farmland with no natural obstruction
to waterfowl flights. Heavy fogs often prevail during the migration
season.
ADVERSE IMPACTS TO WILDLIFE
It is believed that the construction, operation, and maintenance of
Pacific Power's proposed Midpoint to Medford right-of-way and 500 kV
transmission facilities would cause considerable loss of bird life
through collision with lines and towers. Over the life of the project,
the towers, conductors, and shield or groundwires would impose serious
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barriers to birds during migrating, feeding, and courtship flights, and
would kill or cripple birds colliding with them.
Nocturnal avian migrants and local feeding and nesting populations
are especially prone to collisions with man-made objects. Magnitude of
losses depends on tower height, visibility, bird density, and flight
patterns. Birds normally migrate at heights that clear most man-made
obstacles, but when they are blinded or confused, losses occur. This
subject is controversial and needs further study. Arend (1970), in a
report for the Pacific Gas & Electric Company, states that "Electric
power transmission lines mounted on steel towers cause very minor avian
loss, and their adverse ecological impact on avian populations is neg-
ligible." The U.S. Fish and Wildlife Service, however, does not accept
this as a blanket conclusion and has indicated that major losses of
migratory birds would likely occur in areas of intensive use and low-
level flights, such as in the Klamath Basin and Warner Valley. Much of
the published data concerning collisions is based on migrating passerines
striking TV antennas and airport ceilometers. Most radio and TV towers
are above the height of Pacific Power's proposed 500 kV lines and towers.
It is known, however, that during periods of storm and poor visibility,
resident and migrating birds decrease elevation, become confused, and
tend to strike lower structures. Also, waterfowl feeding flights are
usually much lower, making the probability of collisions with power
lines much greater than for migrating birds (Roster 1976, USFWS 1976).
The following are examples of bird losses from collisions:
1. An estimated 50,000 birds died at a ceilometer at the Warner
Robins Air Force Base in Georgia. These birds were all pas-
serines (Johnston and Haines 1957).
2. Thirty thousand birds were estimated killed at a 1000-foot TV tower
during two nights in Eau Claire, Wisconsin; over 10,000
birds, mostly passerines, were actually collected (Kemper
1964).
3. Twenty-one Mute Swan were killed by impact and electrocution
at an overhead power line above a reservoir in England. This
was 30 percent of the total flock (Harrison 1963).
4. In North Dakota, over a period of years, 23 Franklin's Gulls,
and 20 Blue-winged Teal were among the casualties reported at
telephone and power lines by Krapu (1974). More recently
in that State, McKenna and Allard (1976) found 244 birds under
a power line beside a wetland during a 3-month period, and
Schroeder (1977) reported the deaths of 46 Snow and Blue Geese
at a power line beside a plowed field on a single morning.
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5. In both Great Britain (Boyd 1961) and the U.S. (Stout 1967),
Mallards and other dabbling ducks were more often involved in
wire strikes than were diving ducks.
6. Anderson (1978) investigated losses of waterfowl by collisions
with power lines across a 2,155-acre lake near a large power
plant in Illinois. An estimated 400 waterfowl (out of 100,000
present) were killed each fall season. The study concludes
that the mortality was relatively minor in terms of the total
population, because the vast majority of birds had flight
patterns that did not bring them near the power line.
7. Scott et al. (1972) state that in England power lines of 400
kV, 275 kV, and 132 kV "sited near estuaries, in river valleys
or between bodies of water provide a particular hazard when
they lie across the flight paths used by waterfowl, waders,
gulls and other water birds between feeding and roosting
areas." Their 7-year study accounted for a known loss of 1285
birds (including passerines, gulls, rails, and ducks) and the
total mortality may have exceeded 6000.
Commenting on the Klamath Basin situation, the U.S. Fish and Wildlife
Service stated "the greatest threat occurs when large numbers of birds
concentrate in an area for resting, feeding, or nesting purposes. These
birds stay for a period of time ranging from a few days to 3 to 4 months.
Soon after arriving at such an area the birds develop a series of flight
patterns that are not similar to migration flights. These movements are
usually most pronounced between sunset and sunrise when lighting and
visibility are poor. Another characteristic of these flights is the low
elevation at which they occur, especially within or adjacent to the
feeding and resting sites. It is during these local flights that
collisions are most likely to occur rather than during migration flights,
which often cover hundreds of miles nonstop at high elevations. The
problem is increased by inclement weather conditions such as local fog
or snowstorms which restrict visibility and often causes the birds to
fly at low elevations." (USFWS 1976).
While the anticipated loss of waterfowl and other migratory birds
on the proposed line is speculative, the U.S. Fish and Wildlife Service
feels strongly that major losses would probably occur.
Intensive waterfowl flights in the Hagerman area, especially during
migrations down the Snake River, would be subjected to possible losses
due to collisions with the power lines and towers. Birds would be most
vulnerable during periods of low visibility and inclement weather.
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Waterfowl concentrations are found at the Bruneau River crossing
and adjacent C. J. Strike Reservoir, during both feeding activities and
migration. The proposed right-of-way crossing at the Bruneau River
would result in losses similar to those anticipated at Hagerman. Other
birds, such as the Mourning Dove, are vulnerable where an unknown number
of flights would cross the proposed right-of-way. Concentrations of
many other birds are found along the Snake River parallel to the proposed
right-of-way from Hagerman to the Bruneau River, a distance of nearly 60
miles, increasing the likelihood of power line collisions.
A major wildlife concentration occurs at Warner Valley. It is one
of the most vulnerable areas along the proposed Midpoint to Mai in right-
of-way. More than 10,000 waterfowl use the Warner Lakes as a breeding-
feeding area. An unknown, but substantial, number of migrants -- including
other ducks, geese, coots, shorebirds, terns, cranes, pelicans, cormorants,
passerines, and raptors -- pass through this area. In addition, the
area is heavily used by waterfowl, pelicans, and other migrants for
feeding. Annual counts have shown nearly 200,000 birds in the area.
The greatest potential hazard to wildlife would come from placement
of the power line from the west edge of the Klamath Hills to the Worden
area on Highway 97 -- a distance of approximately 7 miles. This part of
the proposed right-of-way would cross the major portion of the migration
route for nearly 5 million waterfowl and thousands of other migratory
birds that move through the Klamath Basin. In addition, an unknown
number of daily feeding flights of resident waterfowl would pass across
the proposed right-of-way. There are no natural obstructions in this 7-
mile area to screen the proposed transmission line or make waterfowl
rise to higher flight elevations. While losses of waterfowl and other
migrants is speculative, the references indicate that substantial losses
will occur (USFWS 1976).
Since the area is also important to breeding birds, there would pro-
bably be losses of ducks during courtship flights. During periods of
poor visibility, such as at night when many migrations and feeding
flights occur, the birds would have a barrier of 11 conductors and
groundwires to fly past along a 14-mile segment of the proposed right-
of-way. Heavy fogs, storms, and wind cause elevation variations in
feeding flights in that area, increasing the possibility of collision.
Besides the waterfowl using this area, gulls and terns, grebes, White
Pelicans, cranes, herons, shorebirds, and passerine species would have to
cross this aerial barrier. Based on losses in other areas, thousands of
birds could be anticipated killed in the Klamath Basin.
In his testimony before the Public Utilities Commission hearings
officer, Roster (1976) described mass feeding flights of nearly 800,000
birds in the Klamath Basin. Since these low elevation flights between
marshlands and grainfields occur at dawn and dusk when visibility is
poor, he believes the proposed power line would present an especially
dangerous obstacle.
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If the birds should change their flight routes to avoid collisions
with the power line, the result could be an adverse economic and rec-
reational impact on Klamath Basin residents, especially if the birds
move across the State line into California (Roster 1976). The U.S. Fish
and Wildlife Service indicates that landowners in Illinois were awarded
compensation of up to $100,000 for decreased hunting opportunity attributed
to a power line. Martinka (1974) states that duck shooting declined by
two-thirds after a power line crossed a Wisconsin hunting area and that
Canada Geese in normal flight would not fly under the line.
As cited above, loss of migrant birds is speculative, and opinions
about the probable magnitude and significance of bird kills vary greatly.
Power Company representatives indicate that minor losses will occur,
contary to what the U.S. Fish and Wildlife Service has indicated.
MITIGATIONS
Of the mitigations cited for wildlife in Chapter IV of the power
line impact statement by the Bureau of Land Management (USDI 1976), only
one pertained indirectly to collisions of waterfowl with conducting
lines and towers. It stated that towers should not be placed in open
expanses of water and marshland, particularly those utilized as flight
lanes, nesting, rearing, or feeding sites by migrating waterfowl and
other birds. It is hoped that this action will mitigate wildlife habitat
destruction, wildlife displacement, and collision with the conductors
and towers.
Overall, it was felt that collisions of waterfowl and passerines
with towers, conductors» and shield wires were an unavoidable wildlife
impact that could not be mitigated. This is especially true at key
migration and feeding sites such as the Snake and Bruneau Rivers, Warner
Valley, and the Klamath Basin.
Long-term impacts are feared, especially if the power line route
selected becomes a transmission corridor through waterfowl and other
migrating bird concentration areas. Adverse effects in migration and
feeding patterns, and direct losses by collisions with towers, conductors,
and shield wires are anticipated. Annual losses would be expected to
continue over the life of the project, especially in the case of multiple
lines or a power corridor (Figure 4).
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Figure 4. General location of proposed route, Malin to Medford.
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ALTERNATE ROUTES
In addition to the proposed route from Midpoint, Idaho to Malin,
Oregon, four alternate routes have been studied, some of which bypass
the Bruneau River and Warner Valley areas. These will not be discussed
in detail. In every case, however, all routes terminate at Malin. In
the segment from Malin to Medford through the Klamath Basin, it is very
difficult to find an alternate route that effectively crosses migration
routes without adverse impacts to the waterfowl flights through the
area.
One alternate route (Route II) parallels the proposed route, passing
slightly to the north, with the same anticipated impacts as for the
proposed route and alternate route I. Alternate route III begins at
Malin, then turns north almost to the city limits of Klamath Falls,
crossing the Klamath River east of the Weyerhauser sawmill, then heads
west north of the proposed route. This route parallels most of the
flyway patterns except for the one-half mile long crossing near Klamath
Falls, where it again bisects major waterfowl flight patterns. It also
crosses Ross's Geese feeding flights in the east side of the Klamath
Basin, and it crosses near the Miller Island Wildlife Management Area in
Oregon.
Alternate route IV dips down into northern California, going south
and west of the Lower Klamath National Wildlife Refuge and close to some
large private hunting clubs. It parallels Sheepy Ridge, an important
hunting area that divides the Lower Klamath Refuge from Tule Lake Refuge.
This refuge area is heavily used by waterfowl, shorebirds, and other
migrants for feeding and nesting, and the alternate route is crossed by
extensive feeding flights near Merrill. Migration flights would probably
be well above the power line since it would be under the crest of or
through some low hills on the south, southeast, and southwest sides of
the Lower Klamath Refuge (Figure 5).
SUMMARY
The problem of waterfowl and other migrants colliding with power
lines is well documented where feeder lines and other small conductors
are concerned, and where TV towers, airport ceilometers, etc., have
caused heavy losses-- especially to passerines in bad weather. The
problem is not well documented where large diameter conductors, bundled
conductors, or large multiple lines are concerned. Based on the literature,
however, heavy losses to waterfowl, cranes, pelicans, other shore and
water birds, as well as migrant passerines are anticipated in areas of
heavy bird concentration, such as in the Klamath Basin.
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1
Figure 5. Alternate power line routes.
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On 21 November 1977, the Secretary of the Interior informed Pacific
Power that the Department of the Interior has determined that alternate
route I, between Midpoint and Mai in, is clearly the preferred one, and
Pacific Power has indicated it will make application for that route.
Between Mai in and Medford, the Secretary recommended alternate route
III, or to construct the project along the proposed route, but he also
indicated to mitigate the impact by undergrounding through the critical
area in the Lower Klamath Basin.
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WORKING GROUP:1 BEHAVIOR
The working group on behavior addressed the aspects of bird behav-
ior that affect bird strike probabilities at power lines, and the group
attempted to identify those circumstances most closely associated with
bird collisions at power lines. This was done whenever possible accord-
ing to bird species grouped into four general categories: (1) water-
fowl, (2) shorebirds, (3) raptors, and (4) small nongame birds.
We first considered the importance of weather conditions in evalu-
ating the risk of power line collision for birds. The weather condi-
tions that influence visibility or detectability of transmission lines
were treated separately from those influencing local movements or mi-
gratory flights. The group generally agreed that low visibility (very
low ceiling of thick clouds and precipitation) is the major weather con-
dition affecting the detectability of transmission lines. Detectability
is influenced by the contrast of the wires or cables against the back-
ground. Weather conditions associated with increased low-level local
movements of birds are basically the same as those that decrease power
line detectability. Waterfowl are generally quite active in such weather
and raptors may move and feed at lower altitudes during low visibility
conditions. The flight activity of passerines probably decreases under
such conditions. There are very few quantitative studies that address
the influence of weather conditions on the amount of local movement in
bird species.
With regard to spring and fall migration, the weather conditions
that contribute to massive movements of birds are well documented (see
Gauthreaux, 1978c). In general, after migrants are aloft in large
numbers and weather conditions deteriorate to those of low ceiling and
visibility, the likelihood of bird strikes at power lines increases.
However, considerable mortality at man-made structures occurs even under
clear skies (e.g., Avery et al. 1977).
The time of day when collisions are most likely to occur largely
depends on the activity cycles of the species. When power line detect-
abil ity is low, birds such as waterfowl and shorebirds moving into
feeding areas at dark or after nightfall on full moon nights are par-
ticularly susceptible. Early morning and late afternoon are usually
periods of considerable flight activity (e.g., roosting flights), but
some raptors are active only after sufficient thermal activity develops
late in the morning. With regard to migratory activity, Gauthreaux
(1978c) has summarized the hour-to-hour variation in the quantity of
migration in species that migrate at night, during the day, or both.
William L. Anderson, Frank Cassel (recorder), Milton Friend, Sid-
ney A. Gauthreaux, Jr. (chairman), Gilbert S. Grant, Donald A. Hammer,
Carl Korschgen, Richard L. Morgan, Richard L. Plunkett, Kent Schreiber,
Bob Wei ford.
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The time of year is also important in assessing the probability of
bird collisions with transmission lines. Courtship activities involving
flight displays increase the chances of collisions. Similarly, the con-
gregations of birds during winter at places of food concentration or in
areas of open water [e.g., "cooling" ponds near nuclear reactors during
winter when other areas are frozen over (Anderson 1978)] strongly in-
crease the chances of birds hitting transmission 1ines. The seasonality
of weather conditions at a locality must also be included in this sec-
tion, because low visibility weather conditions may occur at a particu-
lar time of year at a certain locality. Seasonal migrations will dras-
tically alter the probabilities of bird strikes at transmission 1ines on
a month-to-month basis. The periods of spring and fall migrations
should be of particular concern.
The group considered next the special behavioral characteristics of
bivds that increase their chances of colliding with transmission 1ines.
Raptors that actively pursue prey in flight are probably more vulnerable
to a col 1ision with transmission 1ines than those that do not, but fac-
tors such as size of bird, wing span, and maneuverability (erratic or
straight flight) are also important. The group agreed that when birds
pursue prey, engage in courtship flights, defend a territory, or escape
from a predator, they are particularly prone to collide with a power
line, because they are preoccupied and not very alert to the hazards
that transmission 1ines pose.
The altitude of flight is also an important behavioral character-
istic that contributes to the probability of a collision. For example,
B1 ue-winged Teal are more vulnerable to a col 1ision than are Mallards
because the latter usually fly higher. Local movements of birds are
usually at lower altitudes than migratory movements. During hunting
season, waterfowl fly higher than normally, but they may fly into power
1 ines as a result of being startled (Blokpoel and Hatch 1976). In
migration, birds fly at different altitudes depending on their size, the
time of day, and their destination (Gauthreaux 1978c). During the day,
some species usually fly over transmission 1 ines (e.g., Canada Geese,
larger ducks, gulls), while others often fly under the 1ines (e.g., many
songbirds) unless on a migratory flight. Another aspect to be considered
relates to learning and habituation. Local birds are more 1ikely to
know the location, and perhaps even the danger, of a particular trans-
mission 1ine than transients that will not be so conditioned. Another
point discussed by the working group concerned the closing rate and
maneuverability of a species. Intuitively, it appears that those species
with greater maneuverability have a reduced risk of colliding with
transmission 1ines. Flight speed, wing loading, and other aspects of
bird fl ight should be examined in terms of the species that most fre-
quently hit transmission 1 ines. Little can be said about the differential
risk of power 1ine collisions in flocking and nonflocking species, and
more work is needed in this area.
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The placement of transmission lines is important in assessing the
risk of collision. If possible, transmission lines should be kept on a
single horizontal level with the vertical dimension minimized. Thicker
lines are more conspicuous, and the ground or static lines above trans-
mission lines should be made more conspicuous or put at the level of the
transmission lines. Transmission lines should be kept below the level
of the forest canopy because forest birds have greater maneuverability
in flight and fly slower than those species flying above the level of
the forest canopy (e.g., ducks, raptors, doves). Thus, the former are
less likely to strike power lines. Power lines should never be posi-
tioned just above the level of the forest canopy. Self-supporting
towers present less of a hazard to birds than towers supported by guy
lines. In particularly hazardous areas, power lines should be placed
underground. It should be pointed out that platforms and perches on
power line towers have, under certain circumstances, proved beneficial
to nesting raptors (Gilmer and Wiehe 1977).
Construction of power lines in critical habitats where local or
migratory movements are very predictable should be avoided. Such areas
might include wildlife or waterfowl refuges with large concentrations of
birds, shorelines, mudflats, or entrances to estuaries. Modification of
habitat should be considered with caution. Although fast-growing tree
rows may render power lines less conspicuous and effectively block the
flow of low-flying birds, the ultimate benefit of such a practice should
be carefully evaluated. The working group discussed a specific problem
of power line location in the Phepp's Bend area 100 miles northeast of
Oak Ridge, Tennessee, where a power line will cross a ridge. In this
case the potential risk to migrating raptors along the ridge is of
particular concern. Once again, it was stressed that the power line
should be kept below the level of the canopy as much as possible to
minimize the risk.
Finally the group recommended that the terms corridor and right-
of-way be carefully distinguished. Perhaps a term such as impact area
that is not necessarily as large as a corridor or as small as a right-
of-way should be used in addressing habitat in the power line area. The
impact area would be the area in which power lines and towers have a
behavioral or ecological effect.
The group was in general agreement that more carefully designed and
quantitative studies are needed to fully evaluate the overall impact of
transmission lines on various groups of birds, and that the delibera-
tions of the working group represent but a modest and somewhat hesitant
first step in that direction.
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WORKING GROUP:1 HABITAT
The habitat group considered and discussed four general topics:
(1) relationships between habitats and the frequency of bird strikes,
(2) use of this information in siting transmission and distribution
lines (we did not discriminate between types of overhead lines), (3)
research needed, and (4) general procedures for selecting the best
routes for lines.
A list of more than 80 bird species that have been recorded as
killed by striking utility wires was distributed (Thompson 1978, Table
1). Approximately 50 percent of these species typically inhabit lakes
and marshes. (Species of prairie habitats and of seashore or saltmarsh
ranked second and third, respectively.) Considering the preponderance
of geese, ducks, pelicans, herons, etc. in this mortality and recognizing
the public interest in these birds and their economic, political, and
ecological importance, we discussed primarily the importance of marshes,
ponds, and lakes in the bird strike problem.
The available data indicate that routing lines to avoid wetlands is
desirable, and that the location of these habitats warrants special
attention in any plan for power line siting. In particular, corridors
between two bodies of water or marshes and those that intersect known
flight paths of waterfowl and similar species should be avoided. To
identify these flight paths, intensive studies are needed, especially of
flights of local populations between feeding and resting areas or be-
tween feeding and nesting areas such as heron rookeries. Corridors
across estuaries, because these may be important routes for both local
movements and migrations, should be located only after investigation of
bird movements at all seasons.
In addition to studies of flight paths in local areas, several
other subjects were proposed for needed research. One subject suggested
by the steering committee was the width of the zone on either side of a
transmission line in which birds are vulnerable. This is clearly a sub-
ject for research. However, the vital question is how important to lo-
cal bird populations is mortality from wire strikes. Much more data
will be needed on the mortality of different species in different areas
if resolution of the problem is to be based on a cost-benefit analysis.
We all appreciate the difficulty of obtaining such data, yet at the same
time we believe better decisions would be made if cost-benefit analysis
could be used. We suggest, for practical and political reasons, that
studies of this nature be initiated on waterfowl and later extended to
other species.
Michael L. Avery (recorder), Robert Berg, Bob L. Burkholder, Len
0. Cernohous, Edward Colson, Dale Fowler, J. A. R. Hamilton, Roger
Kroodsma, Jack M. Lee, Jr., Ira D. Luman, Ben Pinkowski, J. T. Tanner
(chairman), William T. Tucker, Jochen H. Wiese.
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Another type of habitat was briefly considered: obvious topograph-
ical features. Ornithologists, especially in Europe, have studied the
migrations of birds through mountain passes and have found that large
numbers of many species migrate both day and night through these passes,
often at very low heights above the ground. There appear to be no data
on birds being killed by wire strikes at these places, but mortality
seems very possible. The group suggests that studies might be made at
ridges, mountain gaps, and other topographical features that tend to
channel or concentrate flight paths.
As in almost all environmental problems, the essential question is
how can information of all sorts, including that from wildlife biolo-
gists and ecologists, be best used to influence decisions, in particu-
lar, the choice of a "best" route for a transmission line. Me urge that
biological and ecological input be introduced into power line planning
at the very earliest stages. In addition to the previous discussion on
the habitats which should be identified for best routing, certain other
areas need to be excluded categorically: National and State parks,
National and State wildlife refuges, wilderness areas, and critical
habitats for endangered species of plants and animals. By compiling an
inventory of the various habitat types and land uses in the area under
study and by categorizing them as to their use and relative importance
to man and to wild species, decision makers should be able to balance
the information to arrive at a "good" decison.
Mentioned above are some of the particular points concerning habi-
tats and transmission lines which need to be included in this inventory
and classification. A conclusion of the working group on mitigation,
that bird losses might be reduced by placing utility lines adjacent, and
parallel, to natural barriers suggests that the location of such barriers
should also be included. We suggest also that it might be practical to
computerize all this information to provide a readily accessible data
base with which the desirability of various alternative routes could be
evaluated.
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WORKING GROUP:1 MITIGATION
The working group on mitigation began its work by examining the
initial notion that power lines can cause significant adverse effects to
waterfowl, raptors, shorebirds, passerines, and threatened and endan-
gered species. The group did not reach a consensus on this, but it did
agree that local areas of potential conflict may occur in any part of
the nation and that conflict in local areas may have national interest.
In other words, there is a national problem with varying local manifes-
tations. However, all transmission lines at potential routes throughout
the Nation do not a priori cause conflict. The committee did think each
of the conflicts was important, but could not or would not deal with
"significance" or "nationalness." The utility members tended to down-
play the importance of the conflicts. (It is not important to them.)
For the conservationists and wildlife biologists, the converse is true.
Possible conflict between power lines and birds is of such impor-
tance that biologists should designate areas in which power line impact
must be studied on a site-specific basis. Because of the difficulty of
this task, the geographic areas that industry engineers believe will be
soonest in jeopardy should be studied first.
SPECIFIC MITIGATION PRACTICES
Using a nominal small group process, we developed a list of 16
mitigation practices (Table 1).
Each method was considered in terms of the following questions:
1. Is this method effective in reducing bird strikes and habitat
destruction?
2. If it is effective only in special conditions, what are they?
3. What costs are involved?
4. What disadvantages are there?
5. Are we confident of the method? If not, what is needed?
6. Is it feasible and worthy of further consideration?
Spencer Amend, Joe Binder, Richard C. Crawford, Ron Freeman (re-
corder), W. Allen Miller, Dean Miller, Larry Thompson (co-chairman),
Richard S. Thorsell, Howard Teasley, Roger Vorderstrasse, Keith H.
Wietecki, Daniel E. Willard (co-chairman).
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Table 1. Suggested practices for mitigating the impacts of transmission
lines on birds.
Methods that simply avoid bird concentration areas in corridor selection.
1. Siting.
2. Upgrading the existing system.
3. Removing conductors.
4. Not building.
5. Creating load-center generation.
Methods that adjust the right-of-way to reduce conflict.
6. Following and being compatible with existing barriers.
7. Scattering lines.
8. Clustering lines.
Methods that modify conductors and structures to reduce the probability
of collision.
9. Diverting birds by modifying habitat and creating alternate
habitat.
10. Placing lines underground.
11. Increasing visibility.
12. Changing conductor configuration.
13. Creating shelter belts.
14. Removing the static wire.
15. Repelling birds with corona noise and predator and distress
calls.
16. Controlling human access.
Compensating for damage to bird populations.
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Consistent with our initial remarks, we caution that solutions must
address specific target species. These measures apply only in cases
where potential collision losses are great enough to warrant the mitiga-
tion expense. We did not address ourselves to a method for making these
comparfsorrs except to note that this problem needs much work.
In contrast to the earlier emphasis on site-specific planning, we
believe that, in the area of physical alterations to transmission facil-
ities, generic solutions are desirable. However, they should be tested
for effectiveness against a reasonable variety of target species and
specific localities.
AVOIDING AREAS OF BIRD CONCENTRATIONS
Obviously, if the power line avoids birds, collisions will be non-
existent. The conditions that make this option most effective include a
variety of considerations. Transmission route planners need to know
early in the planning phase where the significant areas are located.
Areas in which there are high concentrations of birds and areas which
conflict with socially important species should be avoided (e.g., Ross's
Geese, Limpkins, Kirtland's Warblers).
We note that routing around these significant areas is easier when
there are few and localized concentrations along the proposed route.
There are many different and often conflicting interests pressuring
route selectors. Along a proposed route in southwestern Minnesota,
state and federal wildlife experts and sportsmen's groups argue that
this corridor should avoid potholes, sloughs, and marshes that contain
waterfowl. The marshes are surrounded by wheat farms, and farmers do
not want the lines or towers either. This sort of competition from spe-
cial interest groups is not unusual, and routing decisions require hard
data on waterfowl concentration areas. Engineers claim that each ad-
ditional mile of transmission line costs about $250,000, which is passed
on to the rate payer.
Avoiding wildlife concentrations is quite feasible, but it is ab-
solutely essential that they be positively and aggressively delineated,
their locations mapped, and these maps widely circulated. Other land
uses compete and longer lines cost somewhat more, so lir?e routing in-
volves weighty decisions. Because of the complexities and uncertainties
involved, utility planners were eager to discuss such options as not
building the 1ine at all.
Where a suitable line and right-of-way exist, most environmental
impacts can effectively be reduced. System planners routinely consider
this option, as well as the no-build and load-center questions. No-
build and load-center generation can meet or guarantee peak capability
better than base loads.
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Upgrading has long been used when it costs less than new construc-
tion. However, upgrading sometimes costs more, reduces system relia-
bility, and aggravates existing land-use conflicts. The no-build sit-
uation should properly be called "not build this segment," for something
else will be done, at some cost, somewhere else. Load-center generation
may worsen local air quality and deplete the supply of hydrocarbon
fuels.
ADJUSTING THE RIGHT-OF-WAY TO REDUCE COLLISIONS
Two kinds of options were considered in this category: routing to
follow natural barriers and the placement of lines relative to each
other.
Fol1owinq Existing Natural Barriers
Generally, lines placed next to objects that birds already avoid
(for example, along the bases of ridges or along highways) would reduce
the probability of collision. Placing lines within a forest canopy
presents both advantages and disadvantages. With higher voltages,
structures rise well above 100 feet. A line protruding just above the
canopy was thought to be quite dangerous to some species that move
swiftly above the canopy. On the other hand, placing structures below
the top of the canopy would be a hazard for forest species. In addi-
tion, the forest itself will be destroyed along the route. Adverse
aesthetic consequences may also result.
Anything that lengthens a route will increase the cost and require
more land. The latter aggravates the difficulties inherent in the
right-of-way acquisition process. However, lengthening the route is
entirely possible with today's technology.
Line Placement in Relation to Other Lines
The group discussed whether collisions can be reduced through
alternate line placement. Some suggested placing new lines close to
existing lines, making one big hazard rather than two small ones.
Others preferred placing a new line some distance from the first to
reduce the complexity and solidity of the barrier. Observations were
reported to support both views. Either method is feasible, and addi-
tional expense is related only to line length. Higher voltage con-
ductors must have more ground clearance, and systems of widely differing
voltage are less compatible than systems of the same voltage.
MODIFYING CONDUCTORS AND STRUCTURES
The group examined the following eight specific suggestions, many
of which can be used on existing conductors. All assume a fixed route.
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Modifying Habitat
Theoretically, flight routes go from one resource to another. The
suggestion here is that when the flight route and line route conflict,
one of the attractive bird habitats can be moved to reduce the conflict.
The committee reported no evidence to support or deny the usefulness of
this suggestion. Members did, however, have several reservations, and
it is symptomatic of our knowledge that some of the reservations conflict.
Several waterfowl biologists contended that birds fly traditional
patterns and changing them would be difficult. Others noted that flight
patterns change from year to year in response to both changing winds and
land-use practices. Additional costs might arise from land acquisition
or leasing. The suggestion contains no technical limitations.
Placing Conductors Underground
Utility engineers agreed that in situations with no great con-
struction problems, such as shallow bedrock, distribution lines would
not be prohibitively expensive to put underground. However, they felt
strongly that putting higher voltage (110 kV and above) lines under-
ground was still economically and technically impossible. Buried lines
are not reliable, and in rural conditions they are difficult to maintain.
Burying lines disturbs the soil, although no comparison was made
with soil disturbance caused by above ground structures. If cooling oil
leaked, soil organisms would be damaged.
Burying is feasible for distribution lines, but the costs and ad-
vantages should be carefully compared with above ground systems.
Increasing Wire Visibi1ity
There is no data to determine the effectiveness of various devices
for increasing the visibility of conductors and other structures, but
the costs are low and, in some cases, markers could be helpful. These
mitigations merit further investigation. Some devices are summarized
below:
1. Aircraft warning bells are already available; probably effec-
tive in clear, lighted conditions; and cause no harm in low
visibility conditions. However, they may be aesthetically
displeasing to humans.
2. Lighting conductors is technically difficult, aesthetically
displeasing, and perhaps countereffective in poor visibility
situations.
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3. Reducing the size of, and brightly marking, the static wire
presents no technical difficulties or change in new construc-
tion. However, these mitigations have unknown effectiveness
in reducing bird strikes. Because the static wire has been
implicated in many documented collisions, marking it might be
helpful.
4. Coloring conductors is feasible and inexpensive. It could de-
crease collisions and cause no harm. Here, particularly, we
find a conflict in regulatory priorities. Conductors made
more visible to birds are also more visible to humans, and the
national tendency recently has been to reduce the aesthetic
impact of conductors.
5. Strobe lights placed on towers have not been shown to be
effective and are unsightly.
Changing Mire Configurations in Space
The evidence now available does not indicate whether any certain
line height or shape decreases collisions. Bird/wire collisions might
decrease if parallel conductors were at the same level.
Within rather broad technical limits, many configurations are
feasible. It must be remembered, however, that more towers mean more
cost.
Screening Lines with Trees
This would be effective in reducing jeopardy to species that natu-
rally avoid trees. While many forest species are quite agile and avoid
collisions, trees in open country would attract raptors and herons,
which are less agile.
Although this method may be feasible for distribution lines, high-
voltage lines often exceed 100 feet in height. Trees of this size are
not easily acquired or moved. Mass grown trees for use with distribu-
tion lines would not be expensive. The costs should be similar to those
of windbreak trees used in the plains States.
Removing the Static Mire
There is evidence that many birds are killed by collision with this
small high wire; thus, its removal would reduce the probability of
collision.
This suggestion is feasible and reduces line construction costs.
However, the static wire deflects lightning strikes from the conductors.
Because lightning can cause outages, this will work only in lightning-
free areas.
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Repel 1ing Birds
Scare devices have considerable success when birds do not remain in
the area long enough to become accustomed to, and unafraid of, them.
Flocking species appear to acclimate more quickly. There is no evidence
that scare devices attract or disorient birds.
Cost is quite low, and many methods such as flashers, explosions,
predator models, and various noises are available.
Preventing Distractions to Birds
Data indicate that many collisions occur in conditions of good
visibility when the birds are distracted by predators, hunters, or other
human activities. The suggestion was made to eliminate human access to
areas of bird concentration and power lines. The difficulties lie in
enforcement and land-use control. There difficulties make such isolation
impossible except on refuges and other areas already controlled prin-
cipally for wildlife protection purposes. Obviously, this situation
applies only to bird concentration areas near existing lines; new lines
should not be built in such areas.
In those cases in which the land is already regulated, costs are
low. If land acquisition or easements are needed, costs will increase
quickly.
COMPENSATING FOR BIRD LOSSES
A fourth strategy suggested that both habitat and individual birds
are replaceable. When habitat conflicts with lines, that particular
habitat can be sacrificed and other similar habitat purchased. Alter-
natively, game farms can be built so birds can be raised to compensate
for those lost to collision.
The notion seems feasible if one thinks only of those species such
as Mallards, which can be easily raised. In 1978, however, we simply do
not know enough to raise and restore all of the species known to be
killed by power lines. Line builders contend that the number of some
species killed is insignificant and can be ignored.
Habitat replacement is limited by available similar habitat. Many
of our bird concentrations today exist because all other habitat has
been destroyed.
The cost for either of these programs could be inexpensive to very
expensive, depending on local land prices or which species are jeopard-
ized. There was no consensus about who should pay for compensation.
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SUMMARY
Most methods suggested here simply have not been studied enough.
Scientists, though personally convinced the problem is serious, are re-
luctant to take a stand because they lack an empirical basis for any
position. Utility people, thinking of vast sums of money and equipment
involved in mitigation, find little data to convince them to voluntarily
change their route selection priorities.
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WORKING GROUP:1 MANAGEMENT OPTIONS
The group first addressed the question: What is the extent of the
bird/power line problem? The following statement summarizes most of the
substantial comments: "It is the consensus of this group that power
lines have not been proven to be a general hazard to bird movements.
However, there is a high likelihood that adverse impacts would occur in
a limited number of cases and under specific circumstances. Further-
more, although significant mortality may not be proven for most indi-
vidual situations, we recognize the implications of small, cumulative
impacts. The best solution for avoiding significant individual problems
and for minimizing overall adverse impacts appears to lie in early com-
munication between power line planners and wildlife interests. An ac-
ceptable goal would be to identify potential problems far enough in ad-
vance that needed facilities could be constructed with minimum delays
and with minimum adverse impacts on bird movements."
The group's second topic of discussion was an appropriate defini-
tion of management in this context. The first proposed definition was
one limited to the traditional wildlife management approach — i.e., the
manipulation of various factors to produce a desired result. After some
discussion, the definition was broadened to encompass those elements of
power line decision processes that relate to interactions with bird
movements.
The management options identified by the group were, therefore,
three: 1. Determine whether a potential problem exists. 2. Avoid
problem areas. 3. Mitigate.
Mitigation, the subject of another working group, is recognized as
being highly site and species specific. Because the mitigation and
management options groups considered similar situations, we focused on
who has responsibility for exercising the three broad options and when
they should do so. Table 1 suitmarizes various responsibilities, times,
and options discussed.
Several portions of the discussion led to the frustrating conclu-
sion that adequate data bases do not exist in many areas. The problem
was considered by the research priorities working group.
^Spencer Amend (chariman), Michael L. Avery, Robert Berg, Frank
Cassel, Len J. Cernohous, Richard C. Crawford, Dale Fowler, Gilbert S.
Miller, Ben Pinkowski, Richard L. Plunkett, Kent Schreiber, J. T. Tan-
ner, Richard S. Thorsell, Howard Teasley, Roger Vorderstrasse, Keith H.
Wietecki.
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Table 1. Management options (responsibilities, priorities, and timing)
for reducing impacts of transmission lines on birds.
Power line construction phases
Option
Planning3
Construction
Operation
1. Identify potential
problems
A,b B, C
A, B, C
A, B, C
2. Avoid problem areas
A, B, C
A,b B, C
3. Mitigate
A, B, C
A, B, C
A,b B, C
aA Identifies responsibility by utilities to exercise appropriate
option.
B Identifies responsibility by wildlife interests to exercise
appropriate option.
C Identifies responsibility by licensing and regulatory authorities
to exercise appropriate option.
Identifies priority option at each phase.
One suggestion that deserves consideration is that permit approval
might be conditional where a problem is suspected but cannot be proven.
The condition would be that the line be built and monitored and that if
damage is shown to occur, mitigation measures — including compensation
for losses — be initiated.
The final recommendation is that a reporting system utilizing a
standard form be tested by workers in industry, government, and the pri-
vate sector to document bird collisions. This system, if proven work-
able on a small scale, could be expanded to provide a source of useful
data not now available.
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WORKING GROUP:1 RESEARCH PRIORITIES
The work group on research priorities considered five questions.
The essence of these deliberations is provided below.
WHAT GAPS OF KNOWLEDGE EXIST IN DETERMINING THE
IMPACT OF TRANSMISSION LINES ON BIRDS IN FLIGHT?
It is easier to state what is known, rather than what is not known,
in addressing this question. We can state with confidence that birds of
a wide variety of species are killed by collisions with power lines.
These collisions occur in different types of habitats and at a variety
of locations throughout the United States. We also know that the prob-
ability of birds' being in flight is influenced by physical factors such
as weather conditions and patterns and the biological characteristics of
individual species as they relate to time of year, breeding biology, and
feeding behavior. Flight must also occur within the vicinity of power
lines and within an elevation range at which a collision is possible
(the strike zone).
The potential strike zone has three dimensions: the length of the
power line, the vertical plane of wires (perpendicular to the ground),
and the horizontal plane of wires (parallel to the ground). The verti-
cal plane appears to be far more important than the horizontal plane.
However, the latter is important when birds are flushed from below a
power line. Distractions to birds in flight within this zone also
increase the probability for collisions. Distractions include the
active pursuit of food while in flight (e.g., a raptor pursuing a prey
species or an insectivorous feeder pursuing a swarm of invertebrates),
courtship flights (e.g., the pursuit flight of one or more drake Mallards
and a hen Mallard), and escape flights (e.g., the flushing of birds due
to the approach of a predator, aircraft, or man).
Biological and physical characteristics of various avian species
are also important in evaluating the potential for collisions in the
strike zone. The large body size and wing span of eagles, cranes, and
herons result in a large surface area and a higher probability for a
collision with a wire than for blackbirds or teal. However, the visual
acuity of the species; its speed of flight; maneuverability; and whether
its flight tends to be solitary, in loose aggregations, or in dense ag-
gregations interact with body size and wing span as do the weather con-
ditions and distractions described above.
William L. Anderson, Joe Binder, Bob L. Burkholder, Edward W.
Col son, Ron Freeman, Milton Friend (chairman), Sidney A. Gauthreaux,
Jr., Donald A. Hammer, Carl Korschgen, Roger L. Kroodsma, Ira D. Luman,
Richard L. Morgan, Larry S. Thompson, William T. Tucker, Bob Welford,
Jochen H. Wiese, Daniel E. Willard.
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Species that feed their young at the nest, and make feeding flights
through the strike area, have a greater probability for wire strikes
during the nesting season than species that lead their young from the
nest area at hatching. For example, herons must make numerous daily
flights to provide food for both themselves and their young until the
young can leave the nest, while Mallards leave the nest with their
broods as soon as the clutch hatches.
The physical location of power lines relative to daily and migra-
tory flight patterns and the familiarity of the vulnerable population
with the location of these lines influences the probability of collisions.
Resident species, or those in an area for an extended period of time,
undoubtedly learn the location of power lines, thereby reducing their
probability for a collision with these lines from that of migrants pass-
ing through the area. However, a line that separates feeding areas from
resting and roosting areas necessitates that local birds traverse the
strike area at least twice a day.
Even though local birds may be aware of the location of power
lines, this advantage may be lost over time because of the frequency of
travel within the strike zone. Avoidance of the lines from familiarity
can also be negated by weather conditions or an escape flight, during
which time the bird's attention is elsewhere.
We know that habitats for migratory birds are altered by power
lines. What we do not know is the magnitude of bird losses due to col-
lisions with power lines, the long-term effects of habitat alterations
due to the construction of these lines, or the indirect effects on bird
populations and movements that may result from the placement of a power
line at a particular site. Therefore, the biological significance of
power lines cannot be adequately assessed at this time.
It 1s essential to recognize that the number of birds killed is not
by itself an adequate measure of biological significance. The number of
individuals killed at a given location must be related to population
numbers for that species at local, regional, and national levels. For
example, a power line kill of 1,000 Pintails in California has far less
biological significance than the loss of a single California Condor or
the loss of an acre of critical breeding habitat for a threatened or en-
dangered species.
The effects of various physical factors such as visibility, size,
and configuration of lines and the design and height of supporting
structures are totally unknown. Also, the contributions of various
biological factors such as the relative importance of collisions during
migration and local movements, the frequency of collisions within daily
and seasonal time frames, and differences due to behavior and biology
for various species are insufficiently understood to allow comprehensive
evaluations. Even less is known about nonlethal effects of power line
placement: avoidance of areas by birds following the construction of
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power lines, altered migrational movements, altered physiological re-
sponses due to electromagnetic fields, and habitat alterations.
None of the above should be construed to mean that bird collisions
with wires or the placement of power lines are unimportant, only that
many facts remain obscure. These data must be obtained to effectively
evaluate the biological effects of power lines at site-specific loca-
tions (present or planned) and to develop mitigation against bird col-
lisions.
The following key questions represent data gaps that deserve pri-
ority attention:
a. Where are the high risk areas?
b. What are high risk habitats?
c. What is the magnitude of bird collisions with power lines for
the various bird species over specific time periods?
d. What are the effects of power lines on mortality, flight be-
havior, and local distribution of birds; what is the biologi-
cal significance at local, regional, and continental levels?
e. What are the specific conditions that influence the probabil-
ity of bird collisions with power lines?
f. What standard methods are available to develop these missinq
data?
g. What are the relative effects of power lines on birds in mi-
gration, on birds in local movement, and on birds in concen-
trations?
HOW CAN THESE QUESTIONS BE ADDRESSED ON A SHORT-TERM BASIS?
Considerable data are available to evaluate the potential for bird
collisions with power lines. There are deficiencies, however: for
instance, the inadequacy of species and site-specific data for local
situations. Therefore, care must be exercised when extrapolating from
general to specific situations.
Bird movement and bird concentrations are of primary concern in
evaluating the potential for collisions with a proposed power line. Na-
tional and regional information on bird migration patterns and corridors
is available for many species. However, the more local the area, the
more inadequate the information tends to be. Principal information
sources are the United States Fish and Wildlife Service (Migratory Bird
Habitat Laboratory and the Bird Banding Laboratory), various state con-
servation agencies, the Illinois Natural History Survey and others
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involved in radar studies of bird migration, and field guides and other
publications dealing with the seasonal and geographical distribution of
birds.
Bird concentrations for some species can be obtained from various
surveys conducted by natural resource agencies and the National Audubon
Society. Periodic bird counts by local Audubon groups, counts conducted
on national refuges, and aerial surveys by Federal and State conserva-
tion agencies provide local data relative to species diversity and rela-
tive abundance. These and other data sources, fully utilized, will pro-
vide a reasonable evaluation of bird populations within a proposed power
line corridor during various periods of the year.
Information on the types of birds likely to collide with power
lines can be partially obtained from a review of wildlife mortality
data. Primary sources of information include diagnostic laboratory
records, bird rehabilitation and rescue center records, national wild-
life refuge records, field notes, and the scientific literature. United
States Fish and Wildlife Service records on causes of eagle mortality
represent a substantial data base that extends over a broad geographic
area and spans more than 10 years. These data provide an estimate of
the proportion of deaths due to collisions relative to other types of
mortality in the eagles examined.
Mortality data must be interpreted with great caution due to in-
herent biases and variability. It is important to assess the complete-
ness of the examinations leading to the diagnosis of mortality; to know
how representative the birds examined are relative to others that died
and were not examined; and, in some cases, it is important to assess the
qualifications of the investigator who is determining the cause of
mortality.
Despite the inadequacies of mortality data, they are valuable in
evaluating the potential for bird collisions with power lines, so long
as the absence of records documenting collisions of various species is
not interpreted as evidence that those species do not collide with power
lines. Biological characteristics of the species (e.g., size and color-
ation), habitat conditions, scavenger activities, the magnitude of
search efforts to detect mortality, and the type of documentation of
wildlife mortality (personal diary as opposed to publication in the
scientific literature) all influence the data base.
A better understanding of why birds collide with wires and other
inanimate objects is essential to minimize the potential for such col-
lisions. Therefore, considerable insight can be gained by examining
available information on bird collisions with aircraft, radio towers,
buildings, and other objects. Literature searches on these subjects_
will provide information relative to the circumstances involved in bird
collisions and will identify site-specific locations in which long-term
studies have been or are being carried out.
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The effects of power lines on migratory birds extends beyond direct
mortality as a result of collisions. The influence of these lines on
bird migration and behavior is poorly understood but must be considered
in evaluating power line corridors. Electromagnetic effects have been a
subject of continued controversy. Review of the literature on Project
Seafarer (Sanguine) and electric fields currently provides the best in-
formation on electromagnetic effects.
Animal damage studies provide another potential source of data for
understanding bird power line interactions. The Denver Wildlife Re-
search Center of the U.S. Fish and Wildlife Service has pioneered in the
area of electric fields and electronic devices to repulse birds and
animals from crops and livestock. The theoretical considerations in-
volved in these techniques and the results of field and laboratory
testing are relevant to predicting the outcome of bird power line inter-
actions involving electromagnetic fields. These studies are also rele-
vant in developing methods for repulsing birds from power lines.
In addition to using existing data bases more advantageously, a
comprehensive response to each of the seven questions outlined above
should be formulated based on what is already known. Individuals from
various disciplines should be involved to ensure the broad coverage
needed. Publication of these findings would provide a reference manual
to guide power producers, consumers, and natural resource agencies.
Specific information needs regarding what is not known will become read-
ily apparent as a result of this effort.
The development of standard methods for obtaining this information
represents the next logical short-term step. This will help eliminate
differences in interpretation. Part of this step should be the devel-
opment of standard methods for data recording so information can be
gathered at a central location for distribution to all those needing it.
After these procedures have been implemented, a wide variety of individ-
uals can be involved to supplement data gathering.
The short-term approach, then, is to identify specific information
needs, develop standard methods to obtain and record this information,
and return it to specific users through a central data bank. An example
of how this might work involves developing better mortality data regarding
bird collisions with power lines. In this hypothetical example, a
network of diagnostic laboratories specializing in wildlife are identified
to assist in various mortality studies. Field investigators pick up
dead birds in their areas and record a variety of data such as age of
power line, size of the line, and weather conditions during the preceding
and current 24-hour periods prior to submitting this record to the
appropriate diagnostic laboratory with the bird specimens. After necropsy
and laboratory tests, the mortality findings are added to the form, a
copy is kept by the diagnostic laboratory, a copy is returned to the
field investigator, and the original is sent to a central data bank.
Computer retrieval and sorting allow various analyses of the data.
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WHAT LONG-TERM RESEARCH NEEDS TO BE INITIATED
TO EVALUATE THE IMPACT OF TRANSMISSION LINE CORRIDORS?
Until information needs are more specifically defined, only general
comments can be made in response to this question. A combination of
field and laboratory studies will be required to evaluate why birds
collide with wires, how serious the problem is, and what can be done to
reduce the probability of these collisions. Field studies should focus
on the highest predictable risk situations based on current knowledge.
Intensive, long-term (5 to 20 year) studies need to be developed to ad-
dress the entire impact of power lines on bird populations.
These studies should address successive changes 1n the habitat dis-
turbed by construction of a power line and the effects of these changes
on the distribution of bird populations at local, regional, and national
levels; Identify changes in movement patterns as a result of power line
placement; identify differences in response patterns by different species
at different times of the year; and identify differences in effects on
resident and staging bird populations and transients.
Laboratory studies should focus on providing information on why
birds collide with objects. Studies of bird flight and vision are
highly relevant since a greater understanding of these two basic areas
will provide for potential mitigation through revised structural design
of power lines and supporting structures. Other laboratory studies need
to focus on developing recording devices that will automatically record
bird collisions so that better evaluations can be made relative to the
seasonal and daily timing of these collisions and the number of colli-
sions that are immediately fatal. Electromagnetic effects must be
studied to determine if they result in altered physiological functions.
The development of avoidance devices that can be used at high-risk loca-
tions on a continual or seasonal basis to repel birds from power lines
is another area of laboratory research needed.
WHO NEEDS THIS KNOWLEDGE, AND WHO SHOULD FUND THE RESEARCH?
Private utility companies need a sound data base for selecting
power line corridors that have minimal environmental impacts and are
still economically feasible. Resource agencies must have the data to
prepare environmental assessments of proposed power lines. Environmen-
tal groups and others must have access to these data to properly evalu-
ate the environmental impact assessments and statements. Mitigation of
predicted impacts also depends on this data base.
Despite the common need for these data, different orientations of
these groups result in different priorities and, perhaps, different
areas of responsibility. Utility companies should not expect resource
agencies to provide funds or other resources for redesigning and engi-
neering power lines and supporting structures that may be less hazardous
125
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to birds. However, State and federal resource agencies should be pri-
marily responsible for supporting research efforts involving bird popu-
lations, habitat changes, and bird migration. Both groups have an ob-
ligation to support research on the magnitude of bird collisions with
power lines. Basic studies on flight vision, and avoidance mechanisms
(to prevent bird strikes) have implications for many areas of science.
Therefore, these studies appear appropriate for funding by the National
Science Foundation and other such agencies.
HOW SHOULD INFORMATION BE TRANSMITTED?
Effective information exchange on a continuous basis is needed to
reduce the costs and time involved in minimizing current information
gaps. Information must be transmitted rapidly enough for investigators
to take advantage of local field situations and current advances in
technical knowledge. One means is the Center for Short-Lived Phenomena.
Subscribers to this service are immediately sent an Event Notification
Report that provides the date, location, and source of the report along
with a brief description of the event. Issuance of a report is depen-
dent upon the Center's being notified of the event. This notification
system potentially provides interested investigators the opportunity for
on-site data gathering.
The brevity of these Event Notification Reports dictates that other
means of information exchange also be utilized. Establishment of a
quarterly journal, a monthly newsletter, and an annual workshop are
suitable forums for exchanging detailed information. Of the three, the
workshop may be the most useful for the short-term.
126
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WORKSHOP SUMMARY
Stanley H. Anderson
U.S. Fish and Wildlife Service
During the past 2-1/2 days we have gathered to try to evaluate the
impact of bird collisions with transmission lines on avian populations.
The goals have been (1) to determine what we knew about the question,
(2) to find out what results could be expected from known management
techniques, and (3) to determine the areas of uncertainty and the means
of understanding these areas. We have discussed many aspects of these
questions and tried to resolve some of the difficulties. We have sug-
gested short-term solutions and posed questions to establish long-term
efforts to promote a more complete understanding of the subject.
Transmission lines are a source of mortality to bird populations.
However, at this time we have not assimilated the data on the percentage
of population mortality, the effects of scavengers on bird death counts,
or the actual number and biological significance of collisions with
transmission lines.
Further studies of the effects on populations are needed if we are
to understand the complete scope of this question on avian mortality.
Rare or endangered species are of particular concern. The loss of a
single Everglade Kite or Whooping Crane can severely alter those popu-
lations. Most other populations produce more young than the habitat can
maintain. In this case we must determine whether natural population
controls are being partly taken over by transmission line collisions.
These types of data are fairly easy to collect.
Every region has specific problems which require a particular type
of evaluation for proposed transmission lines. Local habitat and bird
behavior must be studied in each region. Planners must consider how
changes in routing, tower design, and land use can reduce avian colli-
sions in each region. Bird maneuverability, seasonal behavioral changes,
flight patterns, and habitat use must be known in normal and adverse
weather conditions.
It is apparent that the limited data currently synthesized are
primarily on raptors and waterfowl because these are conspicuous and
economically important. Even so, their data bases are inadequate to
make reliable decisions on line placement. Data on other species of
birds are virtually nonexistent.
The utility companies are faced with many interest groups when pro-
posing a transmission line. Private land owners, conservationists, and
local and national governments must be satisfied in the planning and
construction phases. While the aesthetics of the lines and towers domi-
nate thinking after government regulations have been satisfied, the
127
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effect of the transmission lines on wildlife, particularly birds, is not
known. The initiation of studies to assist planners and engineers in
placing transmission lines and designing structures that minimize the
impact on birds would satisfy many of the interested groups involved.
We have not yet assimilated all the data on the impact of trans-
mission lines on avian populations. This should be our first order of
business. Next, we should learn more about the techniques to evaluate
flight patterns and use these techniques to provide planners with infor-
mation on desirable and undesirable line locations. We should consider
habitat type and suggest where habitat alteration due to transmission
line siting might be managed to benefit wildlife and where critical hab-
itat or habitat features exist that should be avoided in transmission
line siting. Means of deterring birds in flight from lines and towers
should be investigated. Noise, lights, and colors that are effective in
different regions should be considered. Potential design change in
towers should be studied.
There is a great deal of interest in the power line/avian mortality
relationship as is indicated by the requests for attendance at this
workshop. The concern, however, varies in different regions. As pro-
fessionals, we have an obligation to bring together information and sug-
gest forms of data to answer the questions. This does not mean we need
to have a mass of different data collections, but we must answer basic
questions to help designers and those evaluating the impact of trans-
mission lines to make the best decisions. The question is, then, na-
tional in scope as far as data assimilation techniques and biological
impact are concerned. We are not suggesting national regulations with
additional steps of applications and approval when utility companies
propose transmission lines. Each transmission line siting poses re-
gional questions. Local engineers, planners, and biologists must eval-
uate the routing, the biological, and, ultimately, the social questions
affecting local areas.
128
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DATA BASE ON AVIAN MORTALITY ON MAN-MADE STRUCTURES
Nancy S. Dai ley
Oak Ridge National Laboratory
A computerized data base concerning avian mortality on man-made
structures is available for searching at the Ecological Sciences In-
formation Center of the Information Center Complex, Information Divi-
sion, Oak Ridge National Laboratory. It was sponsored by the U.S. De-
partment of the Interior, Fish and Wildlife Service, National Power
Plant Team, in Ann Arbor, Michigan.
This data base contains bibliographic information on avian mortal-
ity from either collision with or electrocution on man-made structures.
Primary emphasis has been placed on avian collisions with obstacles such
as television and radio towers, airport ceilometers, transmission lines,
and cooling towers. Other structures included are fences, glass walls
and windows, lighthouses, telegraph and telephone wires, buildings,
monuments, smokestacks, and water towers. Various types of studies are
included in the base. Collision studies involve field counts with
identification of victims and field observations of both flight behavior
near structures and avian attraction to lights. Studies which evaluate
migration patterns by using collision data and which describe the impact
of weather on migration and flight patterns have also been included.
Other reports examine the causes of death and injury from impacts,
report victim morphometry and physiology, evaluate species suscepti-
bility to collision, and assess the impact of predation on study reliability.
Related studies describe the impacts on birds from the siting of trans-
mission facilities in wetlands or migratory flyways or provide recommendations
for such sitings. Avian electrocution studies, which cover both electric
transmission structures and electric fences, identify and assess bird
fatalities, examine the activities resulting in death, identify problem
locations and lethal structure designs, and recommend structural modi-
fications to reduce fatalities.
Resources and services of the Ecological Sciences Information Cen-
ter are available to all individuals. Searches are performed without
charge to Department of Energy (DOE) staff members and to researchers
working on directly related DOE-funded projects. Searches are also
performed without charge at the request of the sponsor. For all others,
a fee to cover most costs is assessed. Fees are billed through the
National Technical Information Service, Springfield, Virginia.
Information searches may be initiated by contacting the Ecological
Sciences Information Center and giving complete details of the request.
Specific searches can be performed for authors, corporate author, key-
words, subject categories, geographic location, taxon, and title. Mail
129
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written requests to Nancy S. Dailey or Helen Pfuderer, Ecological Sci-
ences Information Center, Information Center Complex, Oak Ridge National
Laboratory, P.O. Box X, Oak Ridge, Tennessee 37830, or telephone (615)
483-8611, Ext. 3-6173 (FTS: 850-6524). Additional assistance may be
obtained by contacting Gerald Ulrikson, Information Center Complex, Oak
Ridge National Laboratory, Oak Ridge, Tennessee 37830.
Acknowledgement:
Oak Ridge National Laboratory is operated by Union Carbide Corporation
for the U.S. Department of Energy under contract number W-7405-eng-26.
130
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146
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PARTICIPANTS
Working Group Assignments
Mr. Spencer Amend
Kansas Forestry, Fish, and
Game Commission
Route 2, Box 54A
Pratt, Kansas 67124
Dr. Stanley H. Anderson, Section Chief
Migratory Nongame Birds
Migratory Bird and Habitat Research Lab
U.S. Fish and Wildlife Service
Laurel, Maryland 20811
Mr. William L. Anderson
Division of Wildlife Research
Illinois Department of Conservation
605 State Office Building
Springfield, Illinois 62706
Mr. Michael L. Avery
National Power Plant Team
U.S. Fish and Wildlife Service
1451 Green Road
Ann Arbor, Michigan 48105
Mr. Robert Berg
U.S. Fish and Wildlife Service
P.O. Box 1306
Albuquerque, New Mexico 87103
Mr. Joe Binder
Rural Electrification Administration
South Agriculture Building
Room 3323
Washington, D.C. 20250
Mr. Bob L. Burkholder
500 Multnomah, Northeast
Portland, Oregon 97208
Dr. J, Frank Cassel
Zoology Department
North Dakota State University
Fargo, North Dakota 58102
Mitigation, Management Op-
ti ons
Conference Chairman
Behavior, Research Priori-
ties
Habitat, Management Options
Habitat, Management Options
Mitigation, Research Pri-
orities
Habitat, Research Priori-
ties
Behavior, Management Options
147
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Working Group Assignments
Mr. Len J. Cernohous
Bismarck Area Office
U.S. Fish and Wildlife Service
P.O. Box 1897
Bismarck, North Dakota 58501
Mr. Edward W. Col son
Pacific Gas and Electric
3400 Crow Canyon Road
San Ramon, California 94583
Habitat, Management Options
Habitat, Research Priori-
ties
Mr. Richard C. Crawford
Tennessee Valley Authority
Chattanooga, Tennessee 37401
Nancy S. Dai ley
Ecological Science Information Center
ORNL, X-10, Building 2029
Oak Ridge, Tennessee 37830
Mr. Dale K. Fowler
Wildlife Biologist
Tennessee Valley Authority
Norris, Tennessee 37828
Mr. Ron Freeman
Woodward-Clyde Consultants
3489 Kurtz Street
San Diego, California 92110
Dr, Milton Friend
National Fish and Wildlife Health Lab
University of Wisconsin
c/o Department of Veterinary Science
1655 Linden Drive
Madison, Wisconsin 53706
Dr. Sidney A. Gauthreaux, Jr.
Department of Zoology
Clemson University
Clemson, South Carolina 29631
Mitigation, Management Op-
tions
Habitat, Management Options
Mitigation, Research Pri-
orities
Behavior, Research Priori-
ties
Behavior, Research Priori-
ties
Dr. Gilbert S. Grant
University of California
at Los Angeles
Los Angeles, California 90024
Behavior, Management Options
148
-------
Working Group Assignments
Dr. J. A. R. Hamilton
920 Southwest 6th Avenue
Pacific Power and Light Company
Portland, Oregon 97204
Mr. Donald A. Hammer
Division of Forestry, Fisheries and
Wildlife Development
Tennessee Valley Authority
Norris, Tennessee 37828
Dr. Kenneth Hoover
National Power Plant Team
U.S. Fish and Wildlife Service
1451 Green Road
Ann Arbor, Michigan 48105
Dr. Philip L. Johnson, Executive Director
Oak Ridge Associated Universities
P.O. Box 117
Oak Ridge, Tennessee 37830
Mr. Carl Korschgen
U.S. Fish and Wildlife Service
LaCrosse, Wisconsin 54601
Dr. Roger L. Kroodsma
Environmental Sciences Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37830
Mr. Jack M. Lee, Jr., Biologist
Bonneville Power Administration
P.O. Box 3621
Portland, Oregon 97208
Mr. Ira D. Luman
Bureau of Land Management
P.O. Box 2965
Portland, Oregon 97208
Mr. W. Allen Miller
Tennessee Valley Authority
701 Chattanooga Bank Building
Chattanooga, Tennessee 37401
Habftat, Management Options
Behavior, Research Priori-
ties
Steering Committee
Steering Committee
Behavior, Research Priori-
ties
Habitat, Research Priori-
ties
Habitat, Management Options
Habitat, Research Priori-
ties
Mitigation, Management Op-
tions
149
-------
Working Group Assignments
Mr. Dean Miller
Public Service Company of Colorado
P.O. Box 840
Denver, Colorado 80201
Mr. Richard L. Morgan
U.S. Fish and Wildlife Service
2953 West Indian School Road
Phoenix, Arizona 85017
Mr. Ben Pinkowski
NUS Corporation
1910 Cochran Road
Pittsburgh, Pennsylvania 15220
Dr. R. Kent Schreiber
National Power Plant Team
U.S. Fish and Wildlife Service
1451 Green Road
Ann Arbor, Michigan 48105
Dr. J. T. Tanner
Department of Zoology
University of Tennessee
Knoxville, Tennessee 37916
Mr. Larry S. Thompson
Biological Science Coordinator
Energy Planning Division
Montana Department of Natural Re-
sources and Conservation
32 South Ewing
Helena, Montana 59601
Mr. Richard S. Thorsell
Edison Electric Institute
1140 Connecticut Avenue, Northwest
Washington, D.C. 20036
Mr. Howard Teasley
Economic Research
Public Utility Commission of Oregon
Labor and Industries Building
Salem, Oregon 97310
Mitigation, Management Op-
tions
Behavior, Research Priori-
ties
Habitat, Management Options
Behavior, Management Options
Behavior, Management Options
Habitat, Management Options
Mitigation, Research Pri-
ori ti es
Mitigation, Management Op-
tions
Mitigation, Management Op-
tions
Mr. Richard L. Plunkett, Staff Ecologist
National Audubon Society
950 3rd Avenue
New York, New York 10022
150
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Working Group Assignments
Mr. William T. Tucker, Biologist
United Engineers and Constructors
100 Summer Street
Boston, Massachusetts 02110
Mr. Roger Vorderstrasse
U.S. Fish and Wildlife Service
727 Northeast 24th Avenue
Portland, Oregon 97232
Mr. Jochen H. Wiese
P.O. Box 7808
Newark, Delaware 19711
Mr. Keith H. Wietecki
Project Supervisor
Transmission Line Routing
Northern States Power Company
414 Nicollet Mall
Minneapolis, Minnesota 55401
Dr. Daniel E. Willard
School of Public and Environmental
Affairs
Indiana University
Bloomington, Indiana 47401
Habitat, Research Priori-
ties
Mitigation, Management Op-
tions
Behavior, Research Priori-
ties
Habitat, Research Priorities
Mitigation, Management Op-
tions
Mitigation, Research Pri-
orities
Mr. Bob Wei ford
Office of Biological Services
U.S. Fish and Wildlife Service, Region III
Federal Building, Fort Snelling
Twin Cities, Minnesota 55111
151
& U.S. GOVERNMENT PRINTING OFFICE: IB78-753-83B
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