Northern Prairie Wildlife Research Center
Factors Associated with Duck Nest Success
in the Prairie Pothole Region of Canada
Mortality of Adult Ducks
Dead ducks whose remains we collected probably represent only a small portion
of the actual number of ducks that died on our study areas (Sargeant et al. 1984,
Murphy 1993). Remains often were inconspicuous and easily overlooked, and we visited
study areas only at widely spaced intervals. It is not surprising that we found
no duck remains at coyote dens; adult coyotes feed their young mostly by regurgitation
of food consumed elsewhere (Bekoff 1977). Some raptors may be more strongly implicated
than we determined; we examined <10% of the raptor nest bowls for food remains.
Based on locations and types of recovery sites, observations of feeding predators,
abundance of predator species, and published accounts (McInvaille and Keith 1974,
Schmutz et al. 1980, Sargeant and Arnold 1984), we believe the red fox, coyote,
northern harrier, Swainson's hawk, red-tailed hawk, and great horned owl were
most strongly implicated in mortality of adult ducks. Although mink also are major
predators of adult ducks in the PPR (Eberhardt 1973, Eberhardt and Sargeant 1977)
they probably were of little consequence during our study because they were absent
from most study areas during drought (Sargeant et al. 1993).
We believe mallards and northern pintails were most abundant among dead ducks
in relation to breeding populations because they begin nesting earlier than
other dabbling ducks when nesting cover and prey often are scant. We interpret
the preponderance of females among dead ducks to reflect their heightened vulnerability
to predation during nesting. Sowls (1955:117) suggested that mortality of nesting
females ducks may contribute to imbalanced sex ratios in breeding populations.
Johnson and Sargeant (1977) demonstrated that mortality of nesting female mallards
could explain imbalanced sex ratios common in that species (Bellrose et al.
1961). Mallard females in our study easily could have experienced the 20-30%
mortality rate reported in North Dakota (Johnson and Sargeant 1977, Cowardin
et al. 1985) or the 40% mortality rate in the PPR of Canada and Minnesota during
the present study (Blohm et al. 1987).
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