Social monogamy is common among birds, while genetic monogamy is supposed to be rare. I have investigated the genetic mating system of the Black-headed Gull Larus ridibundus in which, as in seabirds and most other long-lived and socially monogamous birds, extra-pair paternity (EPP) is typically rather infrequent. The parentage of 79 chicks from 30 broods was determined based on the analysis of six microsatellite markers. In this study population, evidence of allelic inconsistencies between putative parents and chicks as a result of both EPP and intraspecific brood parasitism (ISBP) was found in 43% of nests . Extra-pair paternity was detected in 33% (10/30) of broods, and 20% (16/79) of all nestlings were sired by extra-pair males. In addition, 9% (7/79) of chicks out of five nests (17%) were not the offspring of either member of the pair, indicating ISBP. These findings reveal a moderate rate of ISBP and a high rate of EPP in the Black-headed Gull compared with other related species and shows that the Black-headed Gulls successfully participate in extra-pair copulations.
Ležalová-Piálková, R. (2011). Molecular evidence for extra-pair paternity and intraspecific brood parasitism in the Black-headed Gull. Journal of Ornithology, 152(2), 291–295. https://doi.org/10.1007/s10336-010-0581-1