BODY TEMPERATURES OF WHITE-FOOTED MICE IN RELATION TO ENVIRONMENTAL TEMPERATURE AND HEAT AND COLD STRESS

Abstract

1. Observations were made on behavior responses and body temperatures of white-footed mice, Peromyscus leucopus noveboracensis, subjected to ambient temperatures ranging from - 35° C. to + 50° C.2. Behavior responses to low temperature included gnawing, grooming movements, running, rapid breathing and shivering. Motor activity was greatest upon initial exposure to cold and at moderately low temperatures (0° to - 20° C.) and decreased almost entirely at lower temperatures (- 20° to - 35° C.). Behavior responses to high temperatures involved a decrease in activity and assumption of postures which exposed the maximum body surface area. Salivation occurred quite freely at temperatures between 40° and 50° C.3. The lowest minimal recoverable body temperature observed was 10° C. This was an esophageal temperature when the mouse was exposed to air temperatures ranging from - 23° C. to - 12° C. over a period of 65 minutes. Activity was minimal during the entire period of exposure.4. The mean lower lethal body temperature (esophageal) was 4.6° + 0.5° C. (15 determinations). Lower lethal body temperatures ranged from 3.5° to 5.0° C. The lower lethal body temperatures were determined at ambient temperatures ranging from - 12° to - 35° C. and the duration of exposure before death occurred varied from 45 minutes to 8.5 hours. There was, however, no apparent correlation between the lower lethal body temperature and the duration of exposure or ambient temperature. Upper lethal body temperatures of two mice were between 43° and 44° C.5. At room temperatures esophageal temperatures ranged from 35.5° to 40.5° C. with a mean of 38.1° C. for males, and from 35.4° to 40.5° C. with a mean of 37.6° C. for females. The difference between sexes may not be significant.6. Differences between esophageal and subcutaneous body temperatures of individual mice ranged from 0.4° to 1.7° C. The mean difference of 1.2° C. for seven mice remained the same under light anaesthesia although both esophageal and subcutaneous temperatures were subnormal.7. Body temperatures of mice supplied with food and water remained rather constant when the mice were subjected to cold stress, except at ambient temperatures around - 30° C. When food and water were withheld all mice became hypothermic within 12 hours at all temperatures below - 1° C. These findings indicate that ordinary low temperatures may not be critical for small mammals in nature unless they are combined with lack of food, water and possibly shelter. Behavior responses such as huddling, burrowing and nest-building may give enough additional protection to offset most of the adverse effects of low air temperatures.