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

Abstract

We studied chick adoption in Audouin's gull, Larus audouinii, a ground-nesting seabird, to test several predictions made by the intergenerational-conflict hypothesis (ICH). The effects of food availability on adoptions were considered by comparing two breeding seasons with differing food supply. As predicted, adoptions were significantly more frequent when food was in shorter supply (48% of broods affected) than when it was more available (18.5%). Adoptions occurred during the first week of the chick-rearing stage; after that, aggression by adults towards intruding chicks increased significantly, which suggests that mechanisms of parent-offspring recognition were established. Foster parents incurred certain costs, since their offspring had lower chances of survival than those in control broods. However, contrary to 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 chicks move only as a response to neighboring chicks being fed by an adult, and in Audouin's gulls, adoptions might be considered reproductive errors.