
21 
: ' a 2 
i bs 
“ae iy 
- 
a7 
>» 
. 2° /- 
oy) 
aay 
i 
Fig. 12. High-quality canvasback wetland in the Minnedosa study area. 
contributing to the fall flight from the study area (estimates 
calculated by multiplying total pairs by hen success and 
ducklings per brood) averaged 7.7/km* (Table 33). 
Summary and Discussion 
Breeding Populations 
Breeding populations of canvasbacks increased from lows 
during the 1958-62 drought to a high in 1965. In 1966 a 
downward trend began that continued through 1972. This 
decrease represented a serious population trend on one of 
the better segments of canvasback habitat in North America 
(Kiel et al, 1972). 
The gradual increase in breeding populations from 1961 
to 1963 may have been due to improved habitat conditions, 
the closed hunting season on canvasbacks in the United 
States from 1960 to 1964 (Geis and Crissey 1969), and high 
productivity of hens in 1962 and 1963, or a combination 
of all of these variables. Stabilized canvasback population 
levels from 1963 to 1965 may have been a result of improve- 
ment of canvasback habitat throughout the Canadian 
prairie wetland area. Although the true value is difficult 
to determine, the Minnedosa area may have approached 
maximum carrying capacity for canvasbacks at 3.9 or 4.3 
pairs/km?, 
The decrease in breeding pairs in 1966 may have been 
caused by poor production in 1965. Further reduction in 
the breeding population in 1967, however, is difficult to 
explain because of the excellent production in 1966 and be- 
cause habitat conditions appeared to be adequate. The 
reduction in breeding pairs in 1967 was possibly due to a 
decrease in acreage of nest cover brought about by exten- 
