Testing the intergenerational conflict hypothesis: factors affecting adoptions in Audouin's gulls, Larus audouinii

We studied chick adoption in Audouin's gull, Larus audouinii, a ground-nest ing seabird, to test several predictions made by the intergenerational-conf lict hypothesis (ICH). The effects of food availability on adoptions were c onsidered by comparing two breeding seasons with differing food supply. As predicted, adoptions were significantly more frequent when food was in shor ter supply (48% of broods affected) than when it was more available (18.5%) . Adoptions occurred during the first week of the chick-rearing stage; afte r that, aggression by adults towards intruding chicks increased significant ly, which suggests that mechanisms of parent-offspring recognition were est ablished. Foster parents incurred certain costs, since their offspring had lower chances of survival than those in control broods. However, contrary t o the ICH hypothesis, adoptees did not select foster broods in relation to the age of the resident chicks. Survival of wandering chicks was no higher than that of chicks who stayed in their natal brood. Results suggest that c hicks move only as a response to neighboring chicks being fed by an adult, and in Audouin's gulls, adoptions might be considered reproductive errors.