Corticosterone mediates carry-over effects between breeding and migration in the kittiwake Rissa tridactyla

Carry-over effects, i.e. when processes in one season influence processes in the next, are believed to have important effects on behavior and fitness in animals. Despite an increasing interest in the identification of carry-over effects, there are few experimental studies of the underlying mechanisms. We investigated how a short-term experimental elevation of the stress hormone corticosterone (CORT) during breeding influences the migratory behavior of black-legged kittiwakes Rissa tridactyla. We exposed chick-rearing kittiwakes to a 3 d elevation of CORT, which is usually secreted in response to food shortages. The migratory behavior of CORT-treated kittiwakes and a control group was then tracked using geolocators. We found that CORT treatment affected subsequent autumn migration in a sex-specific manner. CORT-treated females left the breeding grounds earlier and spent a longer period at the wintering grounds than control birds and CORT-treated males. The CORT treatment did not affect the timing of spring arrival or total length of migration. Our findings indicated that physiological stress incurred during breeding can carry over to affect key parameters of migratory behavior in autumn. Identifying carry-over mechanisms, such as those described here, is important to understand how performance and fitness in animals are determined by interactions between different parts of their life cycle