Energetics of the Prairie Deer Mouse Peromyscus maniculatus bairdii

Abstract

Existence metabolism (EM) of caged mice was measured by subtracting the caloric value of measured fecal and estimated urine losses from food consumed over periods of 2 days when mice maintained constant weight (summer, 18.4 g; winter, 18.1 g). EM (Mkcal = kcal animal^day-1 ) increased significantly with drop in temperature (T = C) and was higher in summer (Mkcal = 19.8 ? 0.447T) than in winter (Mkcal = 18.0 ? 0.447T). Winter-acclimatized animals tolerated temperature extremes of ?5 and +40 C; summer-acclimatized animals, extremes of ?2 and +44 C. Maximum potential metabolism (EM at lower limit of temperature tolerance) averaged 20.5 kcal animal-1 day1. Treadles placed at entrances of burrows showed that free-living mice were active aboveground about 4.3 hr per night in the winter and 2.7 hr during the summer. Using the mean temperatures to which the mice were exposed above ground (winter, ?3; summer, 17.5 C) and in their burrows (winter, 10.7; summer, 20.2 G), we found that energy requirements of free-living adult mice not undergoing reproduction, molting or weight change averaged about 14.3 kcal mouse-1day-1 in the winter and 10.9 kcal in the summer. Body insulation against heat loss was better in winter than summer, as indicated by greater weight and length of hairs and lower rates of metabolism. No significant differences occurred between winter and summer in water or lipid contents of carcasses. Productive energy available for reproduction (maximum potential minus EM at prevailing temperatures) was 5.9 kcal animal^day-1 in winter and 9.8 kcal during tfye