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Predation limits production of ducks in the Prairie Pothole Region, affecting survival of hens, ducklings, and especially eggs. Predation may be sufficiently intense to depress recruitment below replacement levels for mallards (Anas platyrhynchos; Cowardin et al. 1985), and other species of ducks (Greenwood et al. 1987; Klett et al. 1988) in much of the Prairie Pothole Region.

Although predation is the principal cause of failure of duck nests in the Prairie Pothole Region, the abundance of individual predator species and their separate impacts on duck nests have not been quantified. Typically, studies reporting high nest hatch rates for ducks indicated that predators were largely absent; those reporting low hatch rates claimed that many predators of a variety of species were present. High hatch rates have been reported on mammal-free islands (Duebbert 1982; Duebbert et al. 1983), within electrically fenced predator exclosures (Lokemoen et al. 1982), and in areas where predators had been removed (Balser et al. 1968; Duebbert and Kantrud 1974). Because whole complexes of predator species were affected, however, the effects of individual species on duck nests were impossible to discern; an exception is the study of Greenwood (1986), who found that removal of striped skunks resulted in a 10% average increase in hatch rates.

The objectives of this paper are (i) to identify the most important predators affecting upland duck nesting success in the Canadian Prairie Pothole Region and (ii) to assess the influence of selected environmental factors on predation rates. Other papers forthcoming from this study will deal with breeding duck populations, predator distributions and abundance, and differences in nest success among habitats.