Although most owls exhibit biparental care, the relative contributions of males and females during critical life cycle stages are poorly understood. Further information could improve our understanding of the feeding ecology of owls and of mechanisms that govern natural and sexual selection, particularly as they relate to the evolution of reversed sexual dimorphism. The objective of our study was to assess possible intersexual differences in provisioning behavior (visit rate and prey size and type) of slightly dimorphic Eastern Screech-Owls (Megascops asio; females 17% greater mass than males) during the post-brooding period when both adults provision nestlings. Pairs of Eastern Screech-Owls provisioned young with 16 different types of prey in our study with insects and crayfish (Family Astacidae) being the most common. We found no differences between females and males in provisioning rate or in mean size of prey delivered. Our findings suggest Screech-Owls are opportunistic feeders in the post-brooding period and that food niche partitioning does not occur between the sexes. These findings are inconsistent with the Role Differentiation and Ecological Hypotheses made for the evolution of reversed sexual dimorphism but support the Rate Ingestion Hypothesis which predicts that both sexes may take smaller prey during the post-brooding period to increase ingestion rate and decrease handling time. In addition our results contribute to an understanding of the feeding ecology and life history of one of the most widespread and recognizable raptors in North America.
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