Date: 3/1/17 3:35 pm From: James V Remsen <najames...> Subject: [LABIRD-L] LALIT: Red-headed Woodpecker declines
LABIRD: another paper in the most recent Ornithological Applications (Condor) is also relevant to Louisiana birds.
Red-headed Woodpeckers have been declining in Louisiana for a long time. Lowery (1974) stated that it was once one of our commonest woodpeckers but that it had declined dramatically, almost certainly due to Starling competition for nest sites. The BBS data (beginning in 1960s) for Louisiana show strong declines statewide (except for western tier of parishes); most of that decline is post-Lowery 1974. The CBC data, which includes our substantial wintering population, actually show what looks like a slight increase from 1970 through ca. 1990 followed by a steady but slight decline through the present.
The new paper is below. The take-home message is of the 4 hypotheses examined, increasing populations of accipiters, mainly Cooper’s Hawk, best explain the over all decline.
Not mentioned in the paper is that one of the most likely contributors to the explosion in Cooper’s Hawk populations is the dramatic increase in populations of some of their favorite foods, i.e. suburban Mourning Dove populations (the Baton Rouge BBS route showed a doubling of our local suburban population in 25 years), Eurasian Collared-Dove, and White-winged Dove.
Testing alternative hypotheses for the cause of population declines:
The case of the Red-headed Woodpecker
Walter D. Koenig,1,2* Eric L. Walters,3 and Paul G. Rodewald
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
Dr. J. V. Remsen
Prof. of Natural Science and Curator of Birds
Museum of Natural Science/Dept. Biological Sciences
LSU, Baton Rouge, LA 70803