Seasonal body mass fluctuations of captive Tawny Frogmouths (Podargus strigoides) are consistent with seasonal heterothermy

Abstract

Prewinter fat accumulation along with the use of shallow torpor permits the survival of free-ranging Australian Tawny Frogmouths (Podargus strigoides) during winter, when prey availability is low and metabolic costs to maintain high body temperatures increase. Captive studies of these animals currently provide no direct support for this ability. We investigated mass fluctuations of 18 captive birds over 8 years at a North American zoo facility to determine whether or not body mass gains were correlated with seasonality, and subsequently provide indirect evidence for regular torpor use. We found that mass fluctuations were correlated with season, as predicted. The lowest body masses occurred during summer, and the greatest mass occurred during late fall and early winter, based on the seasons of the Northern Hemisphere. We conclude that body fat accumulation by captive Tawny Frogmouths occurs in preparation for winter when, under natural conditions, they regularly use torpor, and that Tawny Frogmouths are capable of altering physiological processes to match the environments in which they live, no matter their Southern Hemisphere origins.