Baseline corticosterone peaks in shorebirds with maximal energy stores formigration: A general preparatory mechanism for rapid behavioral and metabolic transitions?

In captive red knots (Calidris canutus, Scolopacidae) showing a regulated b ody mass increase of 50% related to their migration from temperate staging sites to tundra:breeding grounds, plasma corticosterone concentrations incr eased from less than 10 ng.ml(-1) to levels as high-as 30 ng.ml(-1) when th e energy storage for migration was complete. These birds did not fly, but c oncentrations dropped to very low levels (<5 ng.ml(-1)) as soon as the bird s started their voluntary fasts to the low body masses preceding the early wing and body molts normally occurring after an unsuccessful breeding seaso n. As the elevated levels of corticosterone are associated with stable body mass rather than with the preceding increase or subsequent decrease, it is suggested that a major role of corticosterone during the final stages just before departure may be to prepare birds for long-distance flights. Birds heading into the Arctic to breed face potentially arduous flights into unpr edictable environmental and social conditions. Activation of the hypothalam ic-pituitary-adrenal axis, as measured by elevated levels of corticosterone , may induce the suite of behavioral and metabolic changes necessary to neg otiate these challenges successfully. (C) 2000 Academic Press.