Courtship feedings, copulations and paternity in common terns, Sterna hirundo

Abstract

Over the breeding season, courtship feedings in pairs of common terns were estimated to range from 0 to over 150 and copulations from 0 to over 50 per pair, based on a daylength of 17h. The numbers of both were negatively correlated with laying date, suggesting that late breeding was a consequence of poor-quality males unable to provision their females adequately. Although there was not usually a temporal link between courtship feedings and copulations, overall they were strongly correlated, suggesting that females copulate repeatedly with the same male to gain food. High food availability, as indicated by low tide, was associated with high levels of courtship feeding and few copulations, and vice versa, whereas we did not detect any pattern associated with the time of day. Three of 272 courtship feedings, and two of 76 copulation attempts, were extrapair. Only one of 34 broods contradicted the assumption that broods contained only true siblings, in accordance with the high levels of sexual fidelity observed.