Relation between Low Temperature and Available Food to Survival of Small Rodents

Abstract

During weather small rodents of natural populations may succumb to what may be designated cold weather starvation, the combined effect of low temperature and insufficient food to maintain body temperature. When individuals or groups of prairie deermice (Peromyscus maniculatus bairdi) living in a field in Michigan were without food during a late spring wave, some died of weather starvation (Howard, 1949: 32). Likewise, these and other small rodents confined in live traps during weather frequently die when without adequate food. A small rodent requires more food in proportion to its body weight to maintain body temperature than does a larger animal, since it has a greater proportion of body surface to weight. Small rodents can survive exposure to temperatures far below that of their bodies. They have little or no means of resistance to heat much above their normal body temperature except by remaining in seclusion below ground. It seems unlikely that they voluntarily enter situations where they might die because of exposure to low temperatures. They do venture out in cool weather, however, and then it is necessary to eat several times as much food as in a warmer environment. Under the latter circumstances they may thus exhaust the local food supply and die due to cold weather starvation. This study was initiated at the Laboratory of Vertebrate Biology, University of Michigan, Ann Arbor, and continued at the San Joaquin Experimental Range, O'Neals, California, and in the Division of Zoology at Davis. Drinking water was supplied to all the caged animals in the survival experiments which follow. Acknowledgments are due Lee R. Dice, Oliver P. Pearson, and Tracy I. Storer for critically reading the manuscript. No food or nesting material.-Laboratory and field experiments have shown that many small native rodents cannot survive overnight when exposed to freezing temperatures without food or nesting material. They are unable to break down and utilize fat deposits rapidly enough to maintain body temperatures, and consequently die with little loss in weight (Table 1, Exp. 9; Table 2, Exp. 18). At laboratory temperatures, however, small rodents may survive several days without food or nesting material by utilizing their body fat (Table 1, Exp. 8). When three female Peromyscus maniculatus bairdi were caged together outdoors without food or nesting material, one died during the first day. The minimum temperature had been -1? C. If they had not huddled together all three probably would have died. A female Peromyscus leucopus noveboracensis was confined in a presdwood live trap approximately 3 x 3 x 8 inches without food. The trap was placed on the concrete floor adjacent to an outer wall of the laboratory at 4:15 P.M. on February 6, 1947. Another female was similarly housed, but provided with food. The outdoor temperature dropped to 13? C that night. At 8:00 A.M. the next day the mouse that had been confined without food was nearly dead and unable 300 Vol. 32, No. S