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Factors Associated with Duck Nest Success
in the Prairie Pothole Region of Canada

Discussion


Nest success of the common species was generally low on most areas we studied during 1982-85. Based on suggested threshold rates for stability (Cowardin et al. 1985, Klett et al. 1988), we believe that breeding populations of these species were not self-sustaining in many area-years. Our results are similar to those of other recent studies (Table 17) (Cowardin et al. 1985, Johnson et al. 1987, Klett et al. 1988). These findings suggest that many areas of the PPR of North America are not producing sustainable populations of dabbling ducks.

Table 17. Nest success estimates (%) by habitat class for dabbling ducks in the Prairie Pothole Region of North America.
Study Year and location Species Nest success (%)
Crop- land Grazed grass- land Hay- land Planted cover Wet- land Right- of-way Odd areaa
Cowardin et al. (1985) 1977-80; N.D. mallard <1 12 7 nab 7 3 11
Johnson et al. (1987) 1983; N.D., S.D., Mont. dabbling ducks 3 13 22 19 10 6 10
Klett et al. (1988) 1966-84c; N.D., S.D., Minn. 5 common speciesd 6 14 10 13 14 9 4
Present study 1982-85; Alta., Sask., Manit. 5 common speciesd 2 17e 18 na 16 8 11
aOdd area included patches of cover <2 ha in size and an array of features usually found in Cropland (e.g., rock piles,   gravel borrow pits, narrow borders of upland vegetation around Wetland and along fences between areas of Cropland).
bHabitat class not available.
cWe pooled the annual estimates for all species for period 1980-84 in N.D. and calculated the average, weighted by annual   estimated number of nests initiated.
dMallard, gadwall, blue-winged teal, northern shoveler, and northern pintail.
eWe pooled our annual estimates for our classes Grass and Brush and calculated the overall average for all years.

Because we focused on areas of high mallard densities, our results may not apply generally to the entire Canadian PPR. The relatively high breeding populations of mallards on areas we selected for study suggest that adequate numbers of wetlands were present to support duck populations. Many of our study areas also contained relatively large tracts of native prairie grassland that sometimes was contiguous with an adjacent area of grassland. Ducks associated with large grasslands may have benefited from factors such as relatively favorable predator communities (e.g., dominated by coyotes) (Sovada et al. 1995) and stable amounts of upland vegetation for nesting. If our results are biased because we focused on areas where mallard populations were high and habitat conditions favored duck protection, then we believe they are biased toward the best remaining areas of this important breeding ground, and large portions of this area of Canada may be less suitable for nesting ducks than we observed.


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