Short-term captivity influences maximal cold-induced metabolic rates and their repeatability in summer-acclimatized American goldfinches Spinus tristis

Abstract

Abstract Studies of metabolic variation in birds have involved both wild and captive individuals, but few studies have investigated 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 repeatability in birds is currently uninvestigated. In this study, we measured Msum (maximal cold-induced metabolic rates) in summer 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). Msum 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 produced 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 promoting phenotypically flexible metabolic responses. This suggests that the capacity for phenotypic flexibility varies among individuals, and such variation could have fitness consequences.