We examined baseline and stress-induced changes in plasma corticosterone in relation to body condition and seasonal environmental conditions in three species of cardueline finches wintering in northeastern Oklahoma. Two of these, the Pine Siskin (Spinus pinus) and Purple Finch (Carpodacus purpureus), are irruptive migrants that winter irregularly into Oklahoma, whereas the third, the American Goldfinch (S. tristis), is considered a regular winter resident. Individual turnover of banded birds was high in all three species, which suggests comparable tendencies toward winter transience. Body mass and fat scores of incoming birds increased significantly across the season, peaking in birds captured during midwinter. Baseline corticosterone levels were comparable among species and did not differ seasonally or in relation to daily or weekly temperature fluctuations when the influence of body condition was controlled. By contrast, stress-induced levels of corticosterone secretion varied significantly among species, and changes were correlated with mass- and fat-related indices of body condition. Plasma levels of corticosterone in American Goldfinches and Pine Siskins elevated rapidly during the first 10 min after capture but did not change further, whereas those in Purple Finches continued to rise throughout the 60-min test period. Maximum levels of corticosterone were negatively correlated with residual indices of body condition in American Goldfinches and Pine Siskins, but not in Purple Finches. Interspecific differences in stress-induced elevation of plasma corticosterone and the relationship with body condition are consistent with a possible role of this hormone in modulating foraging activities and, perhaps, local movements of carduelines in response to environmental factors.
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Vol. 129 • No. 3