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8 December 2016 Species-dependent effects of bird feeders on nest predators and nest survival of urban American Robins and Northern Cardinals
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Abstract
The abundance of anthropogenic foods in urban areas offers an excellent opportunity to examine the effects of supplementary food on animal communities, but few studies have examined the consequences of these supplements on relationships between predators and prey. We used observational and experimental approaches to investigate how supplementary food (i.e. bird feeders) affected predator abundances and nest survival of American Robins (Turdus migratorius) and Northern Cardinals (Cardinalis cardinalis) in 7 neighborhoods of Columbus, Ohio, USA. From April to August of 2011–2014, we quantified supplementary foods, the relative abundance of 6 common nest predators, and the nest survival of 2 songbirds. In April–August of 2013 and 2014, we supplemented 3 neighborhoods with additional bird feeders, the supplementary food most frequently available to predators. The effects of bird feeders varied among predator and prey species. Bird feeders were positively associated with the relative abundance of American Crows (Corvus brachyrhynchos) and Brown-headed Cowbirds (Molothrus ater). Neighborhoods with at least 15 feeders had on average 2.7× more crows and 3.2× more cowbirds than neighborhoods with 3 or fewer feeders. Relationships among bird feeders, predators, and nest survival were complex. Nest survival of robins declined with increasing numbers of bird feeders only where crows were most frequently detected. In neighborhoods with the most bird feeders and crows, fewer than 1% of robin nests were expected to survive to fledging (i.e. to 28 days), while in neighborhoods with fewer feeders and/or crows, up to 34% of robin nests were expected to successfully fledge young. In contrast, nest survival rates of cardinals were not related to either feeders or predators. Differences between robins and cardinals in vulnerability to specific predators and diet may partially explain the different patterns that we observed. Thus, although bird feeders generally did not promote nest predation, there may be nuanced and species-specific responses that have the potential to affect common breeding birds.
© 2017 Cooper Ornithological Society.
Jennifer S. Malpass, Amanda D. Rodewald and Stephen N. Matthews "Species-dependent effects of bird feeders on nest predators and nest survival of urban American Robins and Northern Cardinals," The Condor 119(1), (8 December 2016). https://doi.org/10.1650/CONDOR-16-72.1
Received: 5 April 2016; Accepted: 1 September 2016; Published: 8 December 2016
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