The impact of predator exclosures on Snowy Plover nesting success: a seven-year study


161 – 166

1 December 08

Michael A. Hardy, Mark A. Colwell

Michael A. Hardy
Wildlife Department, Humboldt State University, Arcata, CA 95521 USA.


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Nest predation has been identified as a major threat to ground-nesting birds, and predator exclosure cages have been used extensively to protect the nests of some shorebird species. Exclosures are generally effective at reducing egg predation but sometimes have unintended consequences, including nest abandonment and increased predation of incubating adults. We evaluated the effectiveness of exclosures at enhancing productivity of threatened Western Snowy Plovers Charadrius alexandrinus nivosus breeding in coastal northern California from 2001–2007. In coastal beach habitats, exclosed nests survived better than unexclosed nests, and exclosed beach nests survived as well or better than unexclosed nests in higher-quality habitat on riverine gravel bars. There was no significant difference in partial clutch survival or hatchability between exclosed and unexclosed beach nests, and there was no difference in fledging success for chicks that hatched from exclosed or unexclosed beach nests. Exclosed nests experienced significantly higher rates of nest abandonment than unexclosed nests. Although exclosures can greatly increase nest survival, this positive effect could be outweighed by increased nest abandonment or increased predation of incubating adults. Consequently, use of exclosures must  be considered carefully, especially when dealing with threatened species or small, localized populations.