Other species, occasionally recorded as casual 
visitors, include: Whistling Swan, Blue Goose, 
Gadwall, Shoveler, Canvasback, Greater Scaup, 
Oldsquaw, White-winged Scoter, and Red- 
breasted Merganser. 
Most waterfowl prefer impoundments man- 
aged by the summer drawdown technique. 
Common Goldeneyes, Buffleheads, Hooded 
Mergansers, and Common Mergansers may 
be exceptions. Large numbers of Canada 
Geese, Mallards, Black Ducks, and Pintails 
often use interior impoundments for resting 
sites when the impoundments are near im- 
portant feeding grounds, such as large grain 
fields or extensive tidal marshes. Canada 
Geese and American Widgeons also frequently 
forage on nearby pastures and hayfields. 
Canada Geese and dabbling ducks rarely use 
ponds without drawdown zones unless grain- 
fields or other good areas are nearby. Diving 
ducks and mergansers occasionally come to 
ponds without drawdown zones. Spectacular 
concentrations of Mallards, Black Ducks, and 
Wood Ducks occasionally roost in artificial 
ponds that contain fairly dense stands of trees 
and shrubs. 
22 
Wintering waterfowl populations usually 
are sparse on most interior impoundments 
because of the ice. Wood Ducks breed 
on the ponds in most areas where nest 
boxes are provided. Small breeding popula- 
tions of introduced Canada Geese, Mallards, 
and Black Ducks also have become estab- 
lished locally with the help and sur- 
veillance of game managers and biolo- 
gists. 
Sample counts of waterfowl were made on 
two adjoining interior impoundments on the 
Patuxent Wildlife Research Center. During the 
full pool stage, the two ponds covered approxi- 
mately 95 acres, The ponds were drawn down 
during alternate years. Data from several 
counts (selected to show variation in spe- 
cies composition) are shown in table 
15. 
The gullet and gizzard food contents of 54 
waterfowl collected from interior impound- 
ments were examined. In general, dabbling 
ducks preferred vegetable foods and diving 
ducks preferred animal foods. Amore detailed 
discussion of foods is included with the species 
accounts, 
