Periodicity and Energetics of Torpor in the Kangaroo Mouse, Microdipodops Pallidus

The effects of three environmental temperatures and four food rations on the duration and periodicity of torpor were examined, the oxygen consumption of torpid and normothermic kangaroo mice was measured, and temperature profiles in their habitat were obtained during all seasons. Because of their fossorial and nocturnal habits, kangaroo mice need not face environmental temperature above 30°C or much below 0°C although temperatures in their Great Basin habitat normally fluctuate far outside this range. Torpidity affords a reduction in energy expenditure which increases as temperature decreases. At 5°C the oxygen consumption of torpid mice was less than one—sixtieth that of normothermic mice. When the animals were given seeds in excess each day, none became torpid at either 17° or 6°C, but when the daily ration was reduced to 1.5 g all individuals become torpid. The per cent time torpid and the duration of torpor cycles varied inversely with temperature. At 6°C the time in torpor increased when he daily food ration was reduced from 1.5 to 0.5 g but decreased slightly when food in excess was made available at longer intervals. Periods of torpor varied from a few hours to several days. The time in torpor was related to environmental temperature and food supply in such a way that the mice maintained body weight and accumulated food stores under all conditions tested. This suggests that in nature Microdipodops can regulate periods of torpor so as to conserve its stored seeds during both chronic and acute shortages of food.