No evidence for extra-pair paternity in the western gull


L. Gilbert Institute of Biological Sciences, University of Stirling, Stirling FK9 4LA, UK. Fax: +44 (0)1786 464994; E-mail:


The genetic mating system of western gulls Larus occidentalis breeding on Southeast Farallon Island, California, was determined using multilocus DNA fingerprints of 33 chicks from 22 broods. No extra-pair paternity (EPP) was found, despite extra-pair copulations (EPCs) occurring. This suggests that paternity guards are effective, and that females gain few genetic benefits from EPCs. The EPP in western gulls concurs with that of other seabirds, reinforcing the idea that seabirds generally have a monogamous genetic mating system.