Integrating orientation mechanisms, adrenocortical activity, and endurance flight in vagrancy behaviour

Avian migratory processes are typically precisely oriented, yet vagrants are frequently recorded outside their normal range. Wind displaced vagrants often show corrective behaviour, and as an appropriate response is likely adaptive. We investigated the physiological response to vagrancy in passerines. Activation of the emergency life-history stage (ELHS), assessed by high baseline plasma corticosterone, is a potential mechanism to elicit compensatory behaviour in response to challenges resulting from navigational error. We compared circulating plasma corticosterone concentrations and body condition between three migratory groups in autumn: 1) naturally displaced SW vagrants and 2) long distance SE vagrants on the remote Faroe Islands, and 3) birds within the expected SW migratory route (controls) on the Falsterbo peninsula. An ELHS characterized by elevated corticosterone was not generally observed among naturally displaced birds. We found limited support for an increased rate of corticosterone elevation within our 3 minute sample interval in a single species, but overall no differences in corticosterone were detected across groups. Interestingly, fat scores were negatively correlated with circulating corticosterone. The correlation between fat and corticosterone suggest that ELHS activation depends upon individuals’ energetic states. In individuals caught at the completion of an obligate long-distance migratory flight, we found some evidence of corticosterone suppression. Interestingly, limited data did support the induction of negative feedback mechanisms that suppress corticosterone during endurance exercise, even when fuel loads are low.