a 
a 
23 

Fig. 13. Spring burn on a canvasback wetland in the Minnedosa study area. 
had decreased to the 1953-55 low level. The population 
on the Minnedosa area was lowest in 1955, when the 
number of wetlands on the Canadian prairies was high. 
At that time peak canvasback populations were recorded 
on the Redvers and Lousana study areas in Saskatchewan 
and Alberta (Smith 1971; Stoudt 1971). 
Habitat use by breeding pairs is dependent on many fac- 
tors, including size and depth of wetlands; adjacent land 
use; and amount, distribution, and species of emergent 
vegetation in wetlands. These factors may also influence 
the quality and quantity of food present in wetlands. Food 
may be the single most important factor influencing the 
use of wetlands by canvasbacks. Bartonek and Hickey 
(1969a) found that adult canvasbacks fed heavily on sago 
pondweed, caddisfly larvae, and pond snails during the 
breeding season. 
Nesting Parameters 
Although there were annual differences in nest success 
between various wetland size classes, means for the 12-year 
period were consistent. Observations in the field indicated 
that canvasback hens possibly sought the seclusion of smaller 
wetlands for nesting to avoid redheads that continually 
harassed them. Often two or more canvasback hens nested 
in the same small pond, which might indicate a behavioral 
strategy for avoiding redheads or predators. Dzubin (1955) 
and Olson (1964) also reported a preference by canvasback 
females for small nesting wetlands, as did Stoudt (1971) on 
the Redvers study area in Saskatchewan. 
The percentage of canvasback nests in wetlands of 0.4 ha 
or less was highest during early nesting attempts. Larger 
wetlands were used during renesting attempts in June. Hens 
