Role of Corticosterone during migration
Long-distance migration requires many physiological and behavioural adaptations such as changes in muscle enzyme activities, hyperphagia and night activity in otherwise day active migrants. During migration birds alternate between periods of stopover when fuel stores are built up and flight bouts when fuel stores are consumed. Migrants need to switch physiologically and behaviourally between these two opposite states. We investigated whether corticosterone, the most prevalent glucocorticoid in birds, is involved in the regulation of bird migration.
Most migrant birds do not fly in one flight bout from their breeding to some wintering grounds, but they alternate between flight and stopovers. During stopover, birds generally try to build up fuel stores, while during flight fuel stores are partly or completely consumed. Little is known about the hormonal regulation of the energy metabolism during migration and findings so far were often conflicting. During the last years the glucocorticoid hormone corticosterone was discussed as a candidate, which might orchestrate the energetic needs during migration.
We measured plasma corticosterone levels in actively flying migratory birds: in red knots, Calidris canutus, flying up to 10 h in a wind tunnel (collaboration with the University of Lund) and in free-ranging passerines caught out of migratory flight. We compared the plasma corticosterone concentrations of birds with different migration strategies, namely long-distance, short-distance and irruptive migrants. In collaboration with the University of Stockholm experiments manipulating the geomagnetic field in migratory nightingales were performed to investigate whether geomagnetic information is an external cue triggering the physiological adaptations.
During migratory flight, when birds are in a fasting state, slightly elevated baseline levels of corticosterone promote the mobilisation of the energy stores. A strong increase in corticosterone when fat reserves are near exhaustion triggers an increase in the catabolism of protein and probably a change in behaviour. During refuelling when birds are in a resorptive state slightly elevated corticosterone concentrations seem to support fuel deposition. Experiments suggest that this may be triggered by the geomagnetic field, indicating the position in relation to desert and ocean crossings.
Dr. Åke Lindström und Anders Kvist, Universität Lund, Sweden
Dr. Cecilia Kullberg, Dept. of Zoology, Stockholm University
Prof.Dr. Theunis Piersma, Netherlands Institute for Sea Research, Texel, The Netherlands
Prof. Dr. Hubert Schwabl, Washington State University Pullman
Dr. Fernando Spina, Istituto Nazionale per la Fauna Selvatica, Bologna, Italy