The associations among corticosterone levels, energy stores, and stress are highly relevant to bird migration physiology. Many birds maintain elevated baseline corticosterone levels during migration, yet they frequently modulate additional glucocorticoid secretion, probably to protect their flight muscles from catabolism. We report on the adrenocortical response to capture and handling stress in three Accipiter species, the Sharp-shinned Hawk (Accipiter striatus), the Cooper's Hawk (A. cooperii), and the Northern Goshawk (A. gentilis) during fall migration. We found mean baseline corticosterone levels to be similar in Sharp-shinned Hawks and Northern Goshawks, but significantly higher in Cooper's Hawks. Likewise, mean baseline levels of corticosterone did not differ in hatch-year and after-hatch-year male and female Sharp-shinned Hawks and Northern Goshawks, but they were higher in adult male Cooper's Hawks than adult females. Mean corticosterone levels did not increase significantly after 30 min of capture and handling stress in any of the three species, indicating that they modulated their adrenocortical stress responses. Fat scores were not correlated with baseline corticosterone levels, except in Sharp-shinned Hawks, in which elevated baseline corticosterone levels were associated with low fat scores.
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