Seasonal torpor and normothermic energy metabolism in the Eastern chipmunk (Tamias striatus)

To assess the changes in thermoregulatory characteristics that accompany the seasonal expression of torpor we measured seasonal differences in body mass adjustments, body temperature (Tb) and metabolic rate (MR) in both summer- and winter-acclimated individuals from a species of food-storing hibernator, the Eastern chipmunk (Tamias striatus). Torpor occurred only in the winter and was associated with lower normothermic Tb, during inter-bout arousal periods than in the summer. Chipmunks increased body mass before the initiation of torpor in winter, and steadily lost mass as the hibernation season progressed. Torpor expression was correlated to initial mass gain, with the individuals who showed the largest mass increase in the fall showing the highest degree of torpor. Acclimation to winter-like conditions produced a decline in normothermic MR at all ambient temperatures examined. The findings indicate that torpor expression is accompanied by a decrease in Tb and MR during normothermy, indicating that a conservation of energy metabolism occurs, not only in torpor, but also during the inter-bout arousal periods.