摘要
Studies of metabolic variation in birds have involved both wild and captive individuals, but few studies have investi- gated whether captivity directly influences metabolic rates, despite such variation potentially confounding conclusions regarding how metabolic rates respond to the conditions under study. In addition, whether short-term captivity influences metabolic rate re- peatability in birds is currently uninvestigated. In this study, we measured Msum （maximal cold-induced metabolic rates） in sum- mer acclimatized American goldfinches Spinus tristis directly after capture from wild populations, after approximately 2 weeks of indoor captivity （Captive 1）, and again after an additional 1-2 weeks of captivity （Captive 2）. M~ increased significantly （16.9%） following the initial captive period, but remained stable thereafter. Body mass （Mb） also increased significantly （9.2%） during the initial captive period but remained stable thereafter, suggesting that muscle growth and/or remodeling of body composition pro- duced the observed metabolic variation. Mb and Msum were not significantly repeatable between wild and Captive 1 birds, but were significantly repeatable between Captive 1 and Captive 2 groups. These data suggest that caution must be exercised when extrapolating metabolic rates from short-term captive to wild populations. In addition, Msum was a repeatable trait for birds under conditions where mean metabolic rates remained stable, but Msum repeatability disappeared during acclimation to conditions pro- moting phenotypically flexible metabolic responses. This suggests that the capacity for phenotypic flexibility varies among indi- viduals, and such variation could have fitness consequences
