Increasing populations of Double-crested Cormorants (Phalacrocorax auritus; hereafter cormorants) are of concern regarding the displacement of other species from breeding colonies, but little is known about such interactions. Agonistic interactions between ground-nesting cormorants and American White Pelicans (Pelecanus erythrorhynchos; hereafter pelicans) were investigated and compared to those involving cormorants and Herring Gulls (Larus argentatus). Also, a survey of cormorant eggs in nests of other ground-nesting species was conducted. Of 158 agonistic interactions between cormorants and pelicans, 83% were threat displays, 9% attempts to steal nest material and 8% involved some form of physical contact. Pelicans defended their nests less frequently and engaged in fewer physical contacts (8%) in colonies mixed with cormorants compared to areas with only pelicans (33%). Herring Gulls engaged in more physical contact (26%) with cormorants in a mixed colony than when nesting only with other gulls (4%). Cormorant eggs were found in 1–26% of Herring and Ring-billed Gull (L. delawarensis) nests searched in the Great Lakes, and 0.3% of Caspian Tern (Hydroprogne caspia) nests at one location. The results indicate cormorants routinely engage in agonistic interactions with other ground-nesting birds; however, the type and importance of interactions varies. Site- and species-specific evaluation of interactions involving cormorants and other birds is recommended before taking management steps to reduce nest site competition.
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1 June 2011
Interactions Between Double-crested Cormorants and Other Ground-Nesting Species
Christopher M. Somers,
Jennifer L. Doucette,
D. V. Chip Weseloh,
Victoria A. Kjoss,
R. Mark Brigham
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Waterbirds
Vol. 34 • No. 2
June 2011
Vol. 34 • No. 2
June 2011
American white pelican
Caspian tern
competition
Double-crested Cormorant
Herring Gull
nesting colonies
Ring-billed Gull