Effects of Food Availability and Ambient Temperature on Torpor Cycles of Perognathus flavus (Heteromyidae)

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Abstract
This study was designed to determine the extent to which Perognathus flavus becomes hypothermic in response to food shortage and low ambient temperatures. The relationship of foraging and feeding behavior to cycles of torpor is also considered. Animals placed on food rations ranging from 0.25 g/day to 1.5 g/day at temperatures ranging from 1° to 15°C were able to conserve energy by reducing metabolic rate and entering daily periods of torpor. Animals given food in excess at these temperatures did not exhibit torpor. An inverse relationship exists between ambient temperature and food ration versus time in torpor and weight loss. As temperature and food ration decrease, weight loss and length of time in torpor increase. Our data suggest that mid-afternoon feeding on seeds, which have been stored in the burrow, makes it energetically feasible for the animal to devote the earlier evening hours almost exclusively to foraging. This decreases the metabolic costs of foraging because temperatures during these hours are generally higher than those later at night when above-ground activity is greatly reduced. It appears that the tendency to gather and store seeds has high survival value in a habitat characterized by periodically inclement weather and, consequently, an erratic food supply.