ABSTRACT
The peak cold-induced rates of aerobic metabolism of mammals and birds have attracted interest because they directly reflect thermoregulatory thermogenic capacity and may serve as indices of thermogenic endurance. When the goal is to measure the peak rates of aerobic metabolism of free-ranging animals – as during studies of seasonal metabolic rhythms – the question arises as to how soon after capture measurements must be made to avoid captivity-induced alterations. In this chapter, the authors clarify how rapidly the peak rates of oxygen consumption of wild-caught animals are altered by captivity, examining both a mammal and bird: the deer mouse and the black-capped chickadee. The early- and late-retest data sets were analyzed by comparing the total (whole-body) metabolic rates of individuals at initial peak determination and retest – rather than weight-specific rates – because changes in weight-specific rates would likely confound two entirely different processes: changes in the metabolic capacity of preexisting tissues and changes in body weight.
