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Egg Predation, Home Range, and Habitat Selection of American
Crows in a Waterfowl Breeding Area


Department of Wildlife Ecology, 226 Russell Laboratory, University of
Wisconsin, Madison, WI 53706; Department of Animal Ecology, 124
Science II, Iowa State University, Ames, IA 50011

To learn about factors affecting duck nest predation by American crows (Corvus brachyrhynchos), we studied egg predation on artificial nests, home range, and habitat selection of crows in the Prairie Pothole Region of southwestern Manitoba, Canada during the 1986 and 1987 breeding seasons. Predation was higher on nests placed within breeding-crow home ranges than on nests placed at random locations outside of breeding-crow home ranges, but nests placed >700 in from crow nests yet within breeding-crow home ranges were relatively safe from predation. Predation was greater on upland than on overwater nests, and declined after the breeding crows' young had fledged. Nests in low vegetation (<20 cm) were most vulnerable to crows, but increases in cover height above 20-50 cm did not substantially reduce predation. American crows selected woodlots containing coniferous trees for nest-sites more often than expected based on the occurrence of woodlot types on the study area. Home range areas averaged 2.6 km². The maximum distance from the nest attained on foraging flights averaged 382 m; flights longer than 700 m were infrequent. American crows showed large individual variation in their use of foraging habitats, and no significant pattern of use was detected for the study population. American crows seemed to avoid tall vegetation while foraging, and seldom encountered duck nests.
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