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8 February 2017 Testing alternative hypotheses for the cause of population declines: The case of the Red-headed Woodpecker
Walter D. Koenig, Eric L. Walters, Paul G. Rodewald
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The Red-headed Woodpecker (Melanerpes erythrocephalus) has experienced strong population declines during the past 3 decades. Using North American Breeding Bird Survey (BBS) and Audubon Christmas Bird Count (CBC) data, we investigated 4 hypotheses that may explain this decline, including: (1) interspecific competition with native Red-bellied Woodpeckers (Melanerpes carolinus) and nonnative European Starlings (Sturnus vulgaris); (2) predation by Cooper's Hawks (Accipiter cooperii) and Sharp-shinned Hawks (Accipiter striatus); (3) climate change; and (4) changes in forested area within their range. In analyses of both the breeding and overwintering periods, our results indicated a role of increased accipiter populations in driving Red-headed Woodpecker declines through increased predation. We also found evidence for significant effects of warmer winter temperatures and increased forest cover, both directly and indirectly through their effects on enhancing accipiter populations. In contrast, our results failed to support the hypothesis that interspecific competition with either Red-bellied Woodpeckers or European Starlings has played a role in Red-headed Woodpecker declines. Despite considerable evidence for nest-site competition and aggression between Red-headed Woodpeckers and both Red-bellied Woodpeckers and European Starlings, these interactions do not appear to be limiting Red-headed Woodpecker populations.

© 2017 Cooper Ornithological Society.
Walter D. Koenig, Eric L. Walters, and Paul G. Rodewald "Testing alternative hypotheses for the cause of population declines: The case of the Red-headed Woodpecker," The Condor 119(1), 143-154, (8 February 2017).
Received: 3 June 2016; Accepted: 1 December 2016; Published: 8 February 2017

avian declines
climate change
European Starling
habitat change
nest-hole competition
red-bellied woodpecker
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