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 17 h. The numbers of both were negatively co
rrelated with laying date, suggesting that late breeding was a consequence
of poor-quality males unable to provision their females adequately. Althoug
h there was not usually a temporal link between courtship feedings and copu
lations, overall they were strongly correlated, suggesting that females cop
ulate repeatedly with the same male to gain food. High food availability, a
s indicated by low tide, was associated with high levels of courtship feedi
ng and few copulations, and vice versa, whereas we did not detect any patte
rn associated with the time of day. Three of 272 courtship feedings, and tw
o of 76 copulation attempts, were extrapair. Only one of 34 broods contradi
cted the assumption that broods contained only true siblings, in accordance
with the high levels of sexual fidelity observed. (C) 2001 The Association
for the Study of Animal Behaviour.