United States
Environmental Protection
Agency
Chesapeake Bay
Program
Annapolis MD 21403
Research and Development
EPA-600/S3-82-082 Jan. 1983
Project  Summary
Distribution and Abundance of
Waterfowl  and  Submerged
Aquatic  Vegetation  in
Chesapeake  Bay
Robert Munro and Matthew Perry
  Waterfowl populations in Maryland
and Virginia portions of Chesapeake
Bay were examined during long-term
(1890-1970) and current  (1972-
1980) periods to  identify trends in
their distribution and abundance.
Comparisons were also made between
State and Atlantic Flyway populations
and waterfowl species distributions
among survey areas. Distribution and
abundance of submerged aquatic
vegetation (SAV)  among waterfowl
survey areas in Maryland were sum-
marized for seven plant species during
nine years (1971-1979). These data
(SAV species combined) were used to
test the hypothesis that annual varia-
tion in area populations of waterfowl
was related to variation in the abun-
dance of SAV, following an adjustment
for annual variation in the general
abundance of waterfowl. The distribu-
tion and abundance of SAV species
declined in  Maryland  waters  during
the 1970s. There were few statistical-
ly significant relationships between
distribution and abundance of water-
fowl and SAV. But there was an
implied biological  relationship, since
the most important waterfowl winter-
ing areas were also among the most
abundantly vegetated areas. This
report was submitted in partial fulfill-
ment of Interagency Agreement No.
EPA-78-D-X0391  by  the U.S. Fish
and Wildlife Service, Migratory Bird
and Habitat Research Laboratory
under the sponsorship of the Chesa-
peake Bay Program, U.S. Environmen-
tal Protection Agency.
  This Project Summary was devel-
oped  by  EPA's  Chesapeake Bay
Program,  Annapolis,  MD, 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
  The  Chesapeake Bay is the most
important wintering area in the Atlantic
Flyway for more than 1.5 million
waterfowl, including Canada geese
(Branta canadensis), whistling swans
(Cygnus columbianus columbianus).
canvasbacks (Aythya valisineria), ruddy
ducks (Oxyura jamaicensis), common
goldeneyes (Bucephala clangula ameri-
cana),  redheads (Aythya americana).
black ducks (Anas  rubripes), and mal-
lards (Anasplatyrhynchos). The estuary
also serves as a resting area for birds
that migrate farther south. Of the 45 spe-
cies native to North America, 30 migrate
through or winter in Chesapeake Bay.
  Large beds of submerged aquatic
vegetation (SAV), especially widgeon-
grass (Ruppia maritima), wild celery
(Vallisneria americana),and sago pond-
weed (Potamogeton pectinatus), have

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traditionally been important to the Bay's
population of waterfowl. The decline of
the grasses, a major source of food for
the birds, prompted this examination of
historic  and current relationships
between waterfowl and SAV.

Procedure/Methodology
  The U.S. Fish and Wildlife  Service
(USFWS) conducts annual population
surveys of Chesapeake Bay waterfowl.
Although information may be  affected
by weather conditions, birds not found,
and birds found  but not counted, these
surveys constitute the only long-term
source of information on waterfowl
distribution and abundance. These
surveys were analyzed so that popu-
lation comparisons between pre- 1970
(long-term) and 1972-1980 (current)
periods could be made. United States
populations  were used  as baseline
measures to indicate  species trends.
Species had to  compose  at least five
percent of the Atlantic Flyway population
to be considered in this study.
  Waterfowl feeding habits were tabu-
lated according to species, time period
(pre-1960,1960s, and 1970s), and organ
source (gizzard, gullet, or unknown). (See
Table  1.) This information, collected by
Stewart1 during  the  1950s,  Rawls2
during the  1960s, and supplemented
with current data, provided the informa-
tion necessary to examine relationships
between waterfowl and SAV as a food
source.
  Distribution and abundance records of
SAV taken from results of summer
surveys conducted by the USFWS and
Maryland Wildlife Administration during
1971-1979 were studied to determine
the trends of SAV populations. Linear
regression  and analysis  of variance
techniques were used to examine rela-
tionships between waterfowl and SAV.

Results/Conclusions
  Reductions in SAV  populations  af-
fected the distribution and abundance
of waterfowl species that were histori-
cally dependent on SAV and could not
adapt to the changes. Some species left
the area  while  others changed their
feeding habits.
  The SAV  population  as a whole
declined  dramatically in the  1970s.
Vegetated sample stations in Maryland
waters declined  from approximately 29
percent during 1971 to 8 to 15 percent
since  1973.  Important waterfowl food
plants which were abundant during the
late 1960s became less prevalent in the
Bay by 1973. Examples include widgeon-
7able 1.    Summary of the Incidence of Plant Material in the Diet of Waterfowl that
           Winter in Chesapeake Bay
                            Percent plant material, and sample size ()a
Species
Whistling swan
Canada goose
Ruddy duck
Bufflehead
Common goldeneye
Canvasback
Greater scaup
Lesser scaup
Ring-necked duck
Redhead
American Widgeon
Blue-winged teal
Green-winged teal
Black duck
Gadwall
Mallard
Pintail
Pre-1960
74.7
65.2
24.6
53.1
71.3
40.4
51.4
65.4
99.0
97.1
90.7
84.9
74.1
99.0
98.9
97.5
(50f-<
(25)
(20f c
(14)
(47)
(36)
(29)
(17)
/oc |b~c
(OO/
(35)
(21)
(10)
(55)
(21)
(25)
(36)*-'
1960s*
100.0
-
32.6
36.9
52.3
37.2
56.7
94.0
76.6
97.7
-
100.0
93.5
-
94.5
96.4
(221)
( -)
(27)
(45)
(246)
( 9)
(82)
(10)
(77)
(121)
( -)
(13)
(131)
( -)
(134)
(47)
1970s
-
-
20.8
25.1
8.6
32.8
57.9
-
96.6
-
-
91.3
82.6
-
92.7
95.2
'( '-)
( -)
(30)
(21)
(273)
(40)
(76)
( -)
( 7)
( -)
( -)
(29)
(57)
( -)
(84)
(27)
ailnless otherwise noted, aggregate percentages are from gizzard samples.
* Taken from Rawls, C. K. (in prep.). Food habits of waterfowl in the upper Chesapeake
 Bay,  Maryland. University of Maryland Center for Environmental and Estuarine
 Studies.  140 pp.
^Aggregate percentages are from samples for which organs were not recorded.
grass, sago pondweed, horned pondweed
and wild celery.
  Table 2 illustrates trends in Bay grass
populations, among  waterfowl  survey
areas, for nine years. Over 600 sampling
stations of  shoal water habitats were
established to monitor these trends. By
1979 each of the 20 areas had depleted
supplies of SAV. The Lower Choptank
River, for example, had 25.5 percent of
its stations vegetated in 1971. By 1979,
however, this total fell to 12.8 percent.
Eastern Bay, another important winter-
ing area for waterfowl, fell  from 21.4
percent in 1971 to 11.1 percent in 1979.
  Widgeongrass, the most  important
food item of widgeon and black ducks,
was the most  abundant and  widely
distributed species in each of nine
annual  surveys. Low populations  of
widgeon, pintails, and redheads, which
were predominantly vegetarian  in
nature, were correlated with the overall
decline of SAV.
  Diving  ducks,  including  canvasbacks
and  redheads, were most affected by
the SAV decline. Diving  ducks have
small wings and legs set back on their
bodies making walking difficult. They
need water to run across prior to flight
and are thus unable to feed in dense
marshes or agricultural fields. Redhead
populations, which subsist on SAV,
declined  in numbers. Apparently they
could not change their diets and exist in
an area with reduced SAV populations.
Canvasbacks, on the  other hand,
incorporated Baltic clams (Macoma spp)
and other invertebrates into their diets,
and  therefore  remain  as  important
members of the wintering waterfowl
population of the Bay.
  Puddle ducks, which feed by dabbling
at the water's surface, were historically
more dependent on vegetation. Puddle
duck populations,  as a group,  are
presently at one third their former level.
Pintail and widgeon populations are
now  nearly absent from  Maryland
wintering areas. Other puddle ducks,
such as black ducks and mallards, have
also decreased.
  Whistling swans survived the decline
of SAV by foraging  on the land. This
species now depends  more  on  the
availability of unharvested cereal grains
from  agricultural fields than on SAV.
The population of Canada geese contin-
ued a long-term increase  in numbers
during the 1970s. Like swans, Canada
geese rely on cereal grains from fields
around the Bay.


Recommendations
  The declining numbers of waterfowl
that winter in the Chesapeake Bay are
cause for concern. Biological links exist
between abundance of grasses and cer-
tain waterfowl populations in the Bay.

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Table 2.    Frequency Occurrence of Measurable SA V (Species Combined) in Maryland Waterfowl Survey Areas During the Years
           1971-79
                                                  Percent with Vegetation, and Sample Size"
Survey area"
Lower Choptank River
Manokin. Annemessex R.
Chester River
Eastern Bay
Smith Island (Maryland)
Bloodsworth, South
Marsh Island
Patapsco R., Aberdeen P.G.
Honga River
Bayshore. Hooper Island
Magothy - Severn Rivers
Susquehanna Flats
Miles River
Wye River
Little Choptank River
Upper Choptank River
Fishing Bay
Sassafras River
Northeast, Elk,
Bohemia R.
Bayshore, Kent County
Patuxent River
Total
1971
25.5(51)
33.3 (57)
41.7 (36)
21.4(28)
47.1 (17)

27.5 (40)
1.9 (52)
30.0 (30)
39. 1 (23)
33.3 (27)
36.4 (22)
12.5 ( 8)
9. 1 (1 1)
10.0 (30)
11.1 ( 9)
7.9 (25)
20.0 (10)

5.0 (20)
8.3 (12)
0.0 (50)
19.2(624)
1972
20.8 (48)
12.7(55)
13.9 (36)
20.8 (24)
27.3 (1 1)

13.6(44)
0.0 (50)
23.3 (30)
17.4(23)
7.4 (27)
0.0 (30)
37.5 ( 8)
36.4 (1 1)
3.3 (30)
20.0 (10)
O.O (25)
0.0 (10)

0.0 (23)
0.0 ( 6)
0.0 (45)
9.6(613)
1973
14.9 (47)
10.7(56)
14.7(34)
14.3 (28)
25.0 (12)

8.7(46)
2.0 (50)
3.3 (30)
4.3 (23)
14.8 (27)
0.0 (30)
12.5 ( 8)
18.2(11)
0.0 (30)
0.0 (JO)
0.0 (25)
0.0 (10)

0.0 (23)
0.0 (12)
0.0 (50)
6.2(629)
1974
14.3 (49)
17.6(34)
11.8(34)
10.7(28)
23.5(17)

7.0 (43)
3.8 (52)
3.3 (30)
8.7(23)
14.8 (27)
6.7(30)
12.5 ( 8)
36.4 (1 1)
0.0 (30)
0.0 ( 9)
0.0 (25)
0.0 (10)

0.0 (23)
0.0 (12)
2.0 (50)
7.2(610)
1975
0.0
5.8
11.1
14.8
11.8

(47)
(52)
(36)
(27)
(17)

0.0 (43)
4.5
3.4
4.3

6.7
25.0
9.1
0.0
0.0
0.0
0.0

0.0
0.0
(22)
(29)
(23)
( 0)
(30)
( 8)
(11)
(30)
(10)
(24)
(10)

(22)
(12)
0.0 (47)
3.8
(552)
1976
21.7(46)
14.0 (57)
8.6(35)
18.5 (27)
17.6(17)

0.0 (45)
1.9 (52)
3.4 (29)
4.3 (23)
0.0 (25)
0.0 (29)
28. 6 ( 7)
18.2 (1 1)
0.0 (30)
0.0 (10)
0.0 (25)
0.0 (10)

0.0 (22)
0.0 (12)
0.0 (49)
5.7(628)
1977
8.2 (49)
12.5 (56)
16.7(36)
14.8 (27)
0.0(17)

0.0 (46)
7.7(52)
0.0 (30)
4.3 (23 J
7.4 (27)
0.0 (30)
25. Of 8)
9. 1 (1 1)
3.3 (30)
0.0 (10)
0.0 (25)
0.0 (10)

0.0 (23)
0.0 (12)
0.0 (49)
5.0 (638)
1978
6.1 (49)
0.0 (55)
30.6 (36)
11.1 (27)
5.9(17)

0.0 (46)
3.8 (52)
3.3 (30)
0.0 (23)
11.1 (27)
0.0 (29)
12.5 ( 8)
9.1 (11)
3.3 (30)
0.0 (10)
0.0 (25)
0.0 (10)

0.0 (22)
0.0 (12)
0.0 (50)
4.2 (636)
1979
12.8(47)
0.0 (66)
22.2 (36)
1 1. 1 (27)
5.9(17)

0.0 (45)
5.8 (52)
0.0 (30)
0.0 (23)
14.8 (27)
6.9 (29)
0.0 { 8)
9. 1 (1 1)
0.0 (30)
0.0(10)
0.0 (24)
0.0 (10)

0.0 (23)
0.0(12)
0.0 (48)
4.4 (631)
"Data from the files of PWRC, Laurel, Maryland.
"Frequency occurrence of SA V averaged over years, when multiplied by the extent of shoal habitat (<2.44 m at mlw) in an area,
 determined the sequence of survey areas used above.
Decreases in distribution and abun-
dance of SAV directly affect certain spe-
cies of waterfowl. Recovery of SAV re-
sources will encourage the return of
SAV-dependent waterfowl that annual-
ly migrate through the area. Scientists
should continue to study factors leading
to the declension of SAV and how such
changes affect oth'er aspects of the Bay
ecosystem.

References
   1.   Stewart, R.E.  1962. Waterfowl
Populations  in the Upper Chesapeake
Bay.  U.S. Fish  and Wildlife Service.
Special Science Report. Wildlife No. 65.
208 pp.
  2.   Rawls, C.K. In prep. Food Habits
of Waterfowl in Upper Chesapeake Bay
Basin. University of Maryland Center for
Environmental and Estuarine Studies.
140pp.
Robert Munro and Matthew Perry are with the U.S. Fish and Wildlife Service,
  Laurel, MD 20810.
William A. Cook was the EPA Project Officer (for information, see contact
  below).
The complete report, entitled "Distribution and Abundance of Waterfowl and
  Submerged Aquatic Vegetation in Chesapeake Bay," (Order No. PB 82-266
  156; Cost: $16.50, subject to change) will be available only from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield, VA 22161
        Telephone: 703-487-4650
For information contact David Flemer at:
        Chesapeake Bay Program
        2083 West Street, Suite 5G
        Annapolis, MD21403

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Environmental Protection
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