We evaluated hypotheses explaining risk of predation by American Black Bear (Ursus americanus) at 418 Yellow-bellied Sapsucker (Sphyrapicus varius) and Hairy Woodpecker (Picoides villosus) nests, on the basis of nestling begging and nest-site habitat features in Algonquin Provincial Park, Ontario. Ninety-three percent of Yellow-bellied Sapsuckers in stands dominated by Sugar Maple (Acer saccharum) nested in Sugar Maple or American Beech (Fagus grandifolia) trees that were dead or in declining health, whereas 86% of Yellow-bellied Sapsuckers in stands dominated by aspen (Populus spp.) nested in Quaking Aspen (P. tremuloides) that were in declining health. Black Bears depredated 17% of 315 nests of Yellow-bellied Sapsuckers in Sugar Maple stands, which accounts for 71% of all Yellow-bellied Sapsucker nest failures. Only 1 (2%) of 46 Hairy Woodpecker nests in the same Sugar Maple stands was depredated by a bear. None of 51 Yellow-bellied Sapsucker nests in aspen stands was depredated. In Sugar Maple stands, daily nest survival of Yellow-bellied Sapsucker nests was lowest when nestling begging calls were loudest and carried the farthest, in more recently harvested stands, and in trees other than American Beech (mostly Sugar Maple). Nest substrates were hardest at Hairy Woodpecker nests, followed by successful Yellow-bellied Sapsucker nests in American Beech and Quaking Aspen; Yellow-bellied Sapsucker nests were softest in stands that had been harvested within the past 30 years. Our study suggests that the risk of predation by American Black Bears at woodpecker nests is a combined function of nestling begging calls, which attract bears to the nest, and nest habitat characteristics, which influence accessibility to the interior of the cavity.
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Vol. 126 • No. 2