Temperature Selection and Energy Expenditure in the Marsupial Hibernator Cercartetus nanus

Abstract

Torpor is used by many small mammals to reduce energy costs of living. Although it is known that energy savings by employing torpor is temperature-dependent, little is known about temperature selection in hibernators. We investigated the selection of ambient temperature (T_a) in a marsupial hibernator, the eastern pygmy-possum (Cercartetus nanus), in a temperature gradient. We also investigated the consequences of the thermal preferences on energy expenditure during torpor. Cercartetus nanus used torpor frequently in both a low T_a (3–22 °C) or a high T_a (21–37 °C) gradient. The animal often displayed short bouts of torpor at warm areas in the gradient, with an average torpor bout length of less than 8.5 h when food was available and less than 30 h when food was withheld. This selection of a warm T_a for shallow torpor does not minimise the rate of energy expenditure during torpor, although the total energy consumption during a torpor bout is relatively low because of short bout duration. Thus, the use of frequent, brief torpor allows the animal to forage during normothermic periods and reduces overall energy expenditure.