extensive beds of submerged plants or an 
abundant invertebrate fauna, particularly cer- 
tain species of thin-shelled clams and small 
crabs. The fresh-water estuarine bays that 
are frequented by Canvasbacks usually con- 
tain great quantities of wildcelery; in the 
brackish estuarine bays, claspingleaf pond- 
weed, widgeongrass and sago pondweed are 
the predominant species, and large quantities 
of eelgrass occur locally. Canvasbacks are 
common on the brackish estuarine bays of 
Fishing Bay and the Nanticoke River in the 
Blackwater-Nanticoke section. There is very 
little submerged plant growth in these areas, 
but invertebrate animals are abundant, Fairly 
large numbers of Canvasbacks occur in the 
Coastal section, particularly on or near Heines' 
Pond (a large impoundment situated near New- 
port Bay). Small numbers occur in the salt 
estuarine bays of the Lower Eastern Shore 
section, and during migration occasional in- 
dividuals or small flocks may be present on 
interior impoundments for brief periods. 
Brackish estuarine bays are the principal 
wintering habitat. January inventories for 
1955-58 showed the following distribution of 
the wintering populations among the major 
habitat types: brackish estuarine bays - 69% 
(including 58% in areas where submerged 
plants were abundant and 11% on the Black- 
water-Nanticoke areas where there were no 
submerged vascular plants); slightly brackish 
estuarine bays - 16%; fresh estuarine bays - 
7%; coastal impoundment and bay complex - 
5%; and salt estuarine bays - 3%, 
The ecological distribution of Canvasback 
populations during the 1958-59 season is 
shown in table 108. There were very notice- 
able changes in habitat distribution during 
surveys. Birds were most common on the 
fresh estuarine bays during November and 
were fairly common there in December and 
March. The brackish estuarine bay was the 
most used habitat during December, January, 
and March. During midwinter of the 1958-59 
season, the salt-water areas, and particularly 
salt estuarine bays, hadaconsiderably greater 
proportion of Canvasbacks than usual. This 
probably was a result of the severe weather 
during the winter months of the 1958-59 
season. 
Biogeographic Sections 
The average distribution of Canvasbacks 
during the January inventories of 1955-58 is 
shown in table 109. The Eastern Bay section 
apparently is the most important Canvasback 
wintering area in the Upper Chesapeake re- 
gion; other important areas include the Central 
Potomac, Choptank River, Chester River, and 
Blackwater-Nanticoke sections. About 44% of 
the total wintering population of, the region 
was in the central eastern shore area (Chester 
River, Eastern Bay, and Choptank River sec- 
51 
tions); 30% was in the Central Western Shore, 
Potomac, and Patuxent River sections; 13% 
in the southern portion of the eastern shore 
area (Blackwater-Nanticoke and Lower East- 
ern Shore sections); 10% in the northern Chesa- 
peake area (Upper Western Shore, Susquehanna 
Flats, and Upper Eastern Shore sections); and 
5% in the Coastal section. 
Seasonal changes in numbers are shown in 
table 110. The Susquehanna Flats was the 
principal Canvasback area during the early 
part of the fall migration period. Later fall 
migrants were more widely dispersed, and 
occurred chiefly in the Chester River, Central 
Potomac, Upper Western Shore, Choptank 
River, Central Western Shore, and Blackwater- 
Nanticoke sections. The winter was unusually 
severe during 1958-59, and this caused large 
numbers of birds to move tothe Lower Western 
Shore and other sections containing deep es- 
tuarine salt water. Spring migrants were most 
numerous in the Choptank River, Eastern 
Bay, and Susquehanna Flats sections. 
Food Habits 
The gullet and gizzard food contents of 91 
Canvasbacks were examined. Data for 86 of 
these are shown in tables 111-114, In addition 
to these, one bird was collected on the brackish 
estuarine bay of the Patuxent River on Jan- 
uary 2, and four were taken from the coastal 
salt bays near Ocean City during December. 
Principal foods were leaves, stems, and 
rootstalks of submerged plants, seeds of vari- 
ous pondweeds, certain species of mollusks 
and crustaceans, and bait corn. In the fresh 
estuarine bays (table 111), the leaves, stems, 
and rootstalks of wildcelery and other aquatic 
plants were the more important foods; seeds 
of various pondweeds, including sago pondweed 
and claspingleaf pondweed also were con- 
sumed in considerable quantity. In brackish 
estuarine bays of the Chester River, Eastern 
Bay, and Choptank River (table 112), the 
principal foods were various mollusks and 
crustaceans, particularly the bivalve Baltic 
macoma (Macoma balthica) and mud crabs (Xan- 
thidae); leaves, stems, rootstalks and seeds of 
submerged plants, chiefly claspingleaf pond- 
weed; and bait corn, Various mollusks, chiefly 
the Baltic macoma, and bait corn were the 
principal food items in the diet of Canvasbacks 
from brackish estuarine bays of Fishing Bay 
and Nanticoke River (table 113), and from 
salt estuarine bays of the Lower Eastern 
Shore section (table 114}, The four Canvas- 
backs collected on the coastal salt bays near 
Ocean City fed chiefly on corn (bait) and on 
undetermined pelecypod mollusks; they also 
contained seeds of sago pondweed and un- 
determined plant fiber, The Canvasback col- 
lected on the Patuxent River had fed entirely 
on Macoma balthica. 
