United States
Environmental Protection
Agency
Health Effects
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S1 -84-001 Sept. 1984
&EPA Project Summary
Responses of Airborne Biota to
Microwave Transmission from
Satellite Power System (SPS)
Studies were conducted to determine
whether 2.45 GHz microwave radiation
(as would be produced by the proposed
Satellite Power System) constitutes a
hazard to exposed avian species or
influences their survival. Several spe-
cies of birds were used to study a
number of endpoints: aversion/attrac-
tion to the microwave field, change in
migratory orientation, social interac-
tions, lethality, thermoregulatory re-
sponses, molt, foraging behavior,
nesting and reproduction, and effect on
bird flight. In several cases the birds
responded simply to an additional
thermal insult. Some of the effects
found could alter the survivability of the
birds if sufficiently high microwave fields
are encountered. For a few endpoints.
including foraging behavior, migratory
orientation and social interaction, it was
not clear if the modified response was
thermally based. However, these changes
were judged to be small and probably
not critical to survival.
This Project Summary was developed
by EPA's Health Effects Research
Laboratory, Research Triangle Park,
NC, to announce key findings of the
research project that is fully documented
in a separate report of the same title (see
Project Report ordering information at
back).
Introduction
In an effort to find a reliable pollution-
free energy source as an alternative to
fossil fuels, the Department of Energy has
actively examined a number of possible
energy sources. One such source involves
collecting the energy of the sun by
a network of satellites and transmitting it
in the form of microwave energy (2.45
GHz) to rectennas on the earth's surface.
In assessing the environmental impact of
this proposed Satellite Power System
(SPS), the effects of microwaves on
airborne biota is an important considera-
tion. The focus of this report is on the
avian species since birds are commonly
found in areas likely to be selected as
rectenna sites. Further, their complete
freedom of movement precludes prevent-
ing their exposure during flights across
the area or when landing on the rectenna.
The goal of this program is to determine
whether microwave irradiation adversely
alters a wide range of complex avian
behaviors that are essential to their
survival. Effects of 2.45 GHz microwaves
have been studied extensively in mam-
malian species, e.g., rats, mice, rabbits
and monkeys, but very little information is
available for birds. Avian species, gener-
ally, have higher rates of metabolism
(especially during flight), stand on two
feet and have an elongated neck that
increases the amount of isolation between
the head and thorax. All of these
anatomical features can be expected to
increase the susceptibility of birds to
hyperthermia, vestibular and neuromus-
cular dysfunction as well as more subtle
altered behaviors, e.g., inappropriate
migratory behavior due to interference
with normal astronomical or geomagnet-
ic clues.
In this study the experiments were
designed to provide, where possible,
dose-response data for a variety of
different migratory and non-migratory
behavioral and physiologic endpoints.
Non-migratory behaviors include breed-
ing, flocking, feeding and social interac-
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tion among birds. Effects of microwaves
on migratory behavior were evaluated by
comparing the orientation of irradiated
and non-irradiated birds (that normally
migrate) during the time of seasonal
migrations. Finally, experiments were
carried out to determine if birds are able
to perceive and respond to microwave
irradiation, the relationship between
dose and changes in body temperature
under a variety of ambient conditions,
and the relationship between dose and
lethality.
Summary Text
Exposure Facilities
Microwave exposures were conducted
in both indoor (laboratory) and open field
areas. The microwave irradiation facili-
ties were designed to provide plane-wave
illumination with a power density varia-
tion of + 0.5 dB maximum over the cages,
and/or flight area, during all acute and
short-term chronic studies. The radiating
source for all experiments was a standard-
gain horn which provided linearly polar-
ized radiation.
The acute-exposure field studies (at
Manomet Bird Observatory) required only
the illumination ofa15x15x15cm
microwave-transparent cage. Thus, horn-
to-cage spacing of 1.37 meters provided
the required power density uniformity
using a simple overhead mounted horn.
By varying the horn-to-platform spacing,
and by adjusting the microwave power
generator control, the power density at
the surface of the platform could be
varied from about 1 mW/cm2to over 100
mW/cm2. For orientation studies, the
horn was placed on the ground and the
subjects were raised on a microwave-
transparent platform 2.74 meters above
the horn.
The Arthur D. Little (laboratory) facility
required the uniform, simultaneous
illumination of multiple cages of approxi-
mately 1.0 x 1.0 x 0.6 m each. Four such
cages were uniformly illuminated with a
horn-to-cage spacing of at least 7.3
meters. At this spacing, a power density
of 25 mW/cm2 was acheived with a total
radiated power of about 4.6 kW. The
Cober S6F generators, which are 6 kW
microwave power sources, provided
adequate power margin. Measurements
indicated the presence of 180 Hz ampli-
tude modulation which may reach 60
percent at low generator output, <1 kW,
but declines to about 40% above 3 kW
output.
The horns were positioned for overhead
illumination. This configuration, shown
in Figure 1, yielded a power density
Microwave Horn
Waveguide Feed
Anechoic
Lining
Observation
Window (also
one on facing wall)
Casters for
Roll-Out Platform
Figure 1. Microwave irradiation chamber—final design.
variation of ± 1 dB over a floor space of 4' x
6'. A total of five irradiation chambers
were used, together with two replicas for
housing and heating the control birds.
Three of the chambers were operated at
0.1, 1.0 and 10 mW/cm2, for chronic
studies. Another chamber was operated
at 25 mW/cm2 for subchronic exposure
studies while the fifth was used in
conjunction with the wind tunnel and for
those studies involving acute exposures.
An open-jet wind tunnel for study of
birds in flight was designed and built. The
wind tunnel and flight chamber configur-
ation (Figure 2) consisted of two fans,
placed side by side, followed by a
honeycomb flow straightener, a contrac-
tion nozzle, a second flow straightener,
the working chamber, and finally an
outlet diffuser. Upstream fans were used
so that the air velocity in the flight
chamber could be controlled by restric-
ting the air flow to the fans through the
use of blocking lattice-works of different
open area placed in front of the air inlet.
This technique allowed the use of
constant speed fan motors rather than
the variable speed motors used in tunnels
with downstream fans.
For flight training and exposure of
Budgerigars, a 1.0x0.6x0.6m cage with
four solid transparent sides and two
screened ends was placed in the air-
stream of the wind tunnel approximately
0.54 m from the outlet honeycomb flow-
straightener. The flow was adjusted to
provide a velocity of 37 km/h at the level
of the training perch, and a variation of <
2.4 km/h was measured over the remain-
der of the cage.
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Fans
. Air Flow Control Lattice
• Honeycomb Flow Straightener
, Contraction Nozzle
^Restraining (Etectrofiedl
Grid
2 Hydraulic Cylinders
(one on opposite side)
Microwave Transparent
Flight Chamber
Clear Plastic—Sides
Figure 2. Wind tunnel and flight chamber.
A version/A ttraction
These experiments determine if birds
can perceive the presence of microwave
irradiation by observing whether House
Finches (Carpodacus mexicanus) and
Blue Jays (Cyanocitta cristata) exhibit an
attraction or an aversion to the field when
exposed to power densities of 10, 25, and
50 mW/cm2.
At all three power densities. House
Finches showed non-random movement
within the test cage based on the number
of times that birds were observed in the
microwave-irradiated or in the non-
irradiated areas. At 10 mW/cm2, House
Finches exhibited behavior consistent
with attraction to the field by perching
more often in the exposed areas of the
cage during microwave irradation than in
the shielded areas. House Finches, at a
power density of 25 or 50 mW/cm2, were
observed to perch more frequently in the
non-irradiated areas of the cage, sugges-
ting an aversion to the microwave field
(Table 1). Blue Jays also showed non-
random movement within the test cage at
all exposure levels. Birds were observed
in the exposed areas of the cage signifi-
cantly fewer times than in the microwave
shielded areas (Table 2). These results
indicate that Blue Jays exhibit an
aversion to microwave irradiation at all
three power densities. Based on these
results, birds exposed to microwave
irradiation at a rectenna site would
appear to be capable of responding to the
field by either avoidance or attraction
depending upon the power density of the
field and the ambient conditions of
temperature, humidity, wind speed and
solar radiation.
Thermoregulatory Behavior
To investigate the relationship between
microwave exposure and the onset and
duration of patterns of thermoregulatory
behaviors, a series of experiments were
carried out with House Finches (small
bird - 17 to 24 g) and Blue Jays (medium-
sized bird - 75 to 100 g) at each of five
power densities: 0.1, 1, 10, 25 and 50
mW/cm2. Cages were arranged so that
the birds sitting on the perch were
oriented perpendicular to the E vector of
the microwave field. To quantify ther-
moregulatory behavior, birds were ob-
served for one or more of four distinctive
postures which represent behavioral
responses to increasing thermoregulatory
stress.
Cloacal temperature was used as a
measure of body temperature. Each bird's
temperature was monitored continuously
before, during and after 10 minutes of
exposure to microwave radiation. Ambi-
ent temperatures generally remained
within ± 2° (20°C) and there was
essentially no air movement (wind) over
the restrained birds.
House Finches and Blue Jays show
behavioral responses to microwave-
induced heat stress which are good
indicators of increased cloacal tempera-
tures during microwave irradiation. For
both species, studies of behavior and
cloacal temperature indicate that there is
no observable thermoregulatory stress
induced by microwave irradiation of 10
mW/cm2 or less. At 25 mW/cm2 the
larger Blue Jays show more signs of
stress than House Finches. At 50 mW/
cm2, both House Finches and Blue Jays
exhibit signs of thermal stress and show
significant elevation in cloacal tempera-
ture during 10 minutes of irradiation.
Blue Jays showed the larger behavioral
response (Figure 3) suggesting that they
must expend more energy for heat
dissipation than House Finches for
similar rises in cloacal temperature. Both
species experienced significantly greater
elevation in cloacal temperature when
the longitudinal axis of the body was
oriented parallel to the E vector compared
Table 1. Aversion/Attraction of Birds to Microwave Fields - House Finches
*Number of times House Finches were observed
in Area A or B
Power Density
Cage Area
Pre-exposure
Exposure Post-exposure
a) 10mW/cm A Shielded 1104 906 861
B_ Exposed 792 992 912
X ambient temperature = 23.4°C; X relative humidity = 72%
X2 = 51.3, df=2.p <0.01
b) 25 mW/cm2 A Shielded 876 1133 959
B_ Exposed 889 _ 691 735
X ambient temperature = 22.4°C; X relative humidity = 68%
X2 = 56 98, df=2,p< 0.05
c) 50 mW/cm2 A Shielded 860 993 925
B_ Exposed 1012 _ 721 806
X ambient temperature = 21.1°C; X relative humidity = 47%
X2 =5305, df = 2. p <0.01
*The total number of observations of House Finches in a symmetrical cage with two quadrants
shielded from, and two quadrants exposed to, microwave irradiation at 10, 25, and 50 mW/cm2.
The null hypothesis being tested with a X2 analysis (3x2 X2 contingency tables, df=2) is that the
frequency of observations in the shielded and exposed areas of the cage is independent of the
pre-exposure. exposure, and post-exposure periods. Observations were made every six seconds
during the last ten minutes of each 30-mmute period (pre-exposure, exposure, and post-exposure
periods). Birds were observed continuously through a pre-exposure, exposure and post-exposure
period. Each of 10 birds was tested twice.
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Table2. Aversion/Attraction of Birds to Microwave Fields - Blue Jays
*Number of times Blue Jays were observed
in Area A or B
Power Density
Cage Area
Pre-exposure
Exposure Post-exposure
a) WmW/cm2 A Shielded 875 961 996
B_ Exposed 926 _ 505 575
X ambient temperature = 19.1°C; X relative humidity = 44%
X2 = 41.76. df=2,p
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N=10
100
Level 4
0
100
80%
50%
10%
J I I
20%
70%
70%
Level 3
70%
0
100 r-
40%
30% 1 —
ri
70%|
i — 1 I
50C
6
40
%
40%
r~i
20%\
PTI 1
Level 2
40%
50%
20%
0
100r-
40%
70%
Level 1
- 30% 30%
0
100 f-
w%
10%
Level 0
r 50%
40%
60%
70%
90%
50%
30%
70%
_700%
70
Exposure
20
•4—
Post-Exposure
30
I
A B C
Test Period in Minutes
(A = five minutes after onset of irradiation; B = ten minutes after onset of irradiation; C - one minute
after termination of irradiation.)
Figure 3. Percentage of Blue Jays showing stress at each of the five thermoregulatory
response levels during and after irradiation with 50 mW/cm2.
tarsa-metatarsus to the airstream. In
addition, during thermal stress, birds flew
with their mouths open (gaping). If a
Budgerigar showed evidence that it was
clearly unable to maintain flight for the
full 10 minutes, the experiment was
terminated. Thermoregulatory behavior
after flight was ranked according to
severity.
When irradiated at 50 mW/cm2, birds
began to show high levels of stress at
ambient temperatures above 26°C and
demonstrated an inability to fly for 20
mintues at air temperatures above 32°C.
After exposure at air temperatures above
33°C, Budgerigars required at least 10
minutes to recover fully after flight. At air
temperatures above 28°C the birds
irradiated during flight generally showed
higher body temperatures than without
exposure. Based on these data, a micro-
wave field of 50 mW/cm2 could impair
bird flight in the field, forcing the bird to
engage in thermoregulatory behaviors
and land prematurely. The long post-
flight cooling period might adversely
affect a bird's ability to forage or escape
predators. A 50 mW/cm2 power density
is approximately equivalent to an 8°C rise
in ambient temperature to a flying
Budgerigar.
Reproductive Behavior
In view of the likelihood of birds
entering and nesting within the SPS
rectenna site, it was essential to deter-
mine the effects of microwave irradiation
on reproductive success. Bird behavior
for six breeding pairs of Zebra Finches
were characterized as random, mainte-
nance, feeding, reproductive, aggressive
or thermoregulatory. Birds exposed to
continuous microwave radiation (25
mW/cm2) were able to breed successful-
ly. Although the irradiated pairs of Zebra
Finches produced fewer eggs and fewer
fertile eggs, there was no significant
difference in the number of fledglings
produced by the irradiated and control
pairs of birds. This may simply show that
the Zebra Finch already has the ability to
compensate for environmental factors
which may affect its reproductive success.
The effect of 25 or 50 mW/cm2
microwave irradiation on embryonic
development in bird eggs exposed when
incubating parents are absent from the
nest was studied by irradiating fertile
Coturnix Quail eggs twice a day for 30
minutes throughout the 17-day normal
incubation period (for this species). The
hatchability of eggs irradiated by 25
mW/cm2 did not differ from that of
control eggs. No significant differences
were observed in the rates of growth of
chicks hatched from control and 25
mW/cm2 exposed eggs during the first
26-28 days post-hatch nor from control
and 50 mW/cm2 exposed eggs during the
first 15 days post-hatch. No evidence of
teratogenesis was observed as indicated
by the absence of deformed chicks hatched
from eggs that had been irradiated at 25
or 50 mW/cm2. Based on these data,
microwave irradiation by 25 mW/cm2
should not notably reduce egg hatchabil-
ity in the field.
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Results form Cloudy Skies
Results from Clear Skies
Results from Clear and Cloudy Skies (Pooled) for 6.8 and for 23 mW/cm2
Power Density
Treat. mW/cm2
N
A
B
C
D
0
6.8
23
6.8 and
23 (pooled)
* = Non-random Distribution
() - N = number of Birds Tested
[experiments]
indicator of the possible deleterious
effects of microwave irradiation on the
endocrine and autonomic nervous sys-
tems of birds. House Finches were
studied to determine if continuous
microwave exposure alters molting.
All control and exposed birds completed
the molting process. The time required for
the last half of molting was essentially
the same for the controls and the birds
exposed to 1 and 10 mW/cm2. The rate of
molting was slower in the two birds that
were exposed to 25 mW/cm2. Whether the
slower rate of molting resulted from
microwave exposure or some other
variable (e.g., the birds used in these
experiments had already started molting
when trapped and the change in environ-
ment from the wild to the laboratory may
have affected the molting process) will
require additional study.
An examination of control birds and
those exposed at 25 mW/cm2 revealed no
observable gross or histopathologic
changes in any of the major organs that
could be attributed to microwave treat-
ment. Similarly, each bird was observed
for changes in muscle tone, righting
reflex, vestibular function, pupillary
response to light, corneal opacity and
response to pain (cornea). No differences
were observed between control and
irradiated birds.
Figure 4. Mean directions exhibited by groups of birds under various conditions ofcloudcover
and microwave exposure (6.8; 23 mW/cm2).
Social Interaction
The White-throated Sparrow (Zonotri-
chia albiocollis) and the Dark-eyed Junco
(Junco hyemalis) were studied to assess
the effects of acute microwave radiation
on the behavior and position of birds
within a flock dominance hierarchy.
Initial observations provided basic flock
structure data and the dominance order
within the flock. Encounters between
birds were classified as either active
agression or avoidance.
Initially one and later two birds from
five-bird hierarchies were exposed.
Ultimately, 17 birds from 12 flocks were
exposed to 4 combinations of microwave
power and duration, in addition to 3 sham
control birds from 2 additional flocks.
Although the irradiated birds maintained
their positions in the hierarchies (with one
exception), some appeared to have
changed their level of aggression after
exposure at 25 mW/cm2. These changes,
however, are not considered inconsistent
with survival of birds at an SPS rectenna
site.
Lethal Levels of Microwave
Irradiation
The lethal level of microwave irradia-
tion for the Dark-eyed Junco exposed at
an ambient temperature of 7 to 13°C
appears to be on the order of 150-160
mW/cm2 over 7 ± 0.5 minutes based on
exposures at 130,150 and 160 mW/cm2.
Power densities of 100 to 130 mW/cm2
for up to 20 minutes result in no
observable signs of heat stress other than
gaping. Exposure to near lethal levels of
microwave irradiation results in stress-
related behaviors that are characterized by
gaping, panting, crouching and loss of
muscular coordination or equilibrium.
The rapid onset of gaping has been
observed at all power levels from 25
mW/cm2 to 160 mW/cm2 beginning as
soon as 30 seconds after the start of
exposure.
Molt of Birds Exposed to
Microwave Radiation
Molt was chosen as a sensitive
U. S. GOVERNMENT PRINTING OFflCEt 1984/759-102/10711
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This Project Summary was authored by staff of Arthur D. Little, Inc., Cambridge,
MA 02140; Boston University. Boston, MA 02214; and Manomet Bird
Observatory. Manomet, MA 02345.
Daniel F. Cahill and John W. Allis are the EPA Project Officers (see below).
The complete report, entitled "Responses of Airborne Biota to Microwave
Transmission from Satellite Power System (SPS)." (Order No. PB 84-141 191;
Cost: $32.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officers can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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