Hematological condition indexes in greenfinches: effects of captivity and diurnal variation

Ecophysiological research aiming at explaining the causes and consequences of variation in individual condition, health state, and allostasis is traditionally performed on captive animals under controlled laboratory conditions. The question about how captivity per se affects studied parameters is therefore of central importance for generalizing the information gained from such studies. We addressed this question by comparing various indexes of physiological condition of wintering greenfinches sampled in the wild and kept in captivity for different time periods. Bringing wild greenfinches into captivity did not result in systematic alteration in nine of 12 physiological parameters studied. Captive birds had consistently lower plasma carotenoid and uric acid levels than wild ones. Variation in differential leukocyte counts did not reveal any signs of elevated stress of birds kept in captivity. These results indicate that for a number of physiological parameters, information obtained from captive animals can be generalized to natural situations. Variance in traits most closely related to physical exercise capacity (body mass and hematocrit) were much lower in the wild than in captivity. These findings suggest that under harsh environmental conditions experienced by wild birds (i.e., predation threat, scarce resources), traits such as hematocrit and body mass are fine tuned by physiological trade-offs.