High offspring survival of the brown-headed cowbird in an invaded habitat

Authors


Tel: (609) 258 7891; Fax: (609) 258 7892; E-mail: rwinfree@princeton.edu

Abstract

The brood parasitic brown-headed cowbird (Molothrus ater) is considered an important threat to bird conservation in North America because it reduces the reproduction of its numerous host species. Prior to the colonisation of America by Europeans, the cowbird was largely confined to the North American prairie region, but it has since invaded forests and other habitats and is now one of the continent's most abundant breeding passerines. The objective of this study was to examine cowbird reproduction with different host communities to determine whether habitat-specific reproduction might contribute to the cowbird's population expansion. Cowbird offspring survival was estimated with hosts breeding in fragmented deciduous forest (a newly invaded habitat) and old fields (a habitat more similar to the cowbird's original range). Offspring survival was 1.8–3.1 times higher in forest compared to old fields and was high enough to cause the cowbird population to increase with most forest hosts. The results suggest that increased offspring survival in an invaded habitat facilitates cowbird population growth. Land management for extensive, continuous forests, which cowbirds are known to avoid, could help control the cowbird population and reduce parasitism levels for the >140 species of cowbird hosts.

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