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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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