The effect of temperature on the pattern of torpor in a marsupial hibernator.

Physiological variables of torpor are strongly temperature dependent in placental hibernators. This study investigated how changes in air temperature affect the duration of torpor bouts, metabolic rate, body temperature and weight loss of the marsupial hibernator Burramys parvus (50 g) in comparison to a control group held at a constant air temperature of 2 degrees C. The duration of torpor bouts was longest (14.0 +/- 1.0 days) and metabolic rate was lowest (0.033 +/- 0.001 ml O2.g-1 x h-1) at 2 degrees C. At higher air temperatures torpor bouts were significantly shorter and the metabolic rate was higher. When air temperature was reduced to 0 degrees C, torpor bouts also shortened to 6.4 +/- 2.9 days, metabolic rate increased to about eight-fold the values at 2 degrees C, and body temperature was maintained at the regulated minimum of 2.1 +/- 0.2 degrees C. Because air temperature had such a strong effect on hibernation, and in particular energy expenditure, a change in climate would most likely increase winter mortality of this endangered species.