Temperature Regulation in Two Rodents (Clethrionomys gapperi and Peromyscus leucopus) and a Shrew (Blarina brevicauda) Inhabiting the Same Environment

Temperature regulation was measured in the short-tailed shrew (Blarina brevicauda), the red-backed vole (Clethrionomys gapperi), and the white-footed mouse (Peromyscus leucopus) to explain some of the habitat preferences and distribution patterns. All three species weighed about 20 g. As ambient temperature (Ta) decreased, these species exhibited a linear increase in oxygen consumption. The rate of increase of oxygen consumption per °C (conductance) was higher in shrews (0.22 cm³ O₂[g·h·°C]⁻¹) than in voles or mice (both 0.16 cm³ O₂[g·h·°C]⁻¹). Using a new equation for predicting conductance, it was found that most cricetid rodents, including C. gapperi and P. leucopus, have conductances lower than predicted from body mass (Wb). Also, B. brevicauda and most other soricid insectivores have conductances higher than predicted from Wb. The high conductance of B. brevicauda is probably due to high evaporative heat loss. Within the thermal neutral zone (TNZ) metabolic rates of P. leucopus were the same as predicted from Wb. Metabolic rates of C. gapperi and B. brevicauda within the TNZ were 128% and 192% of predicted, respectively. Neither body temperature (Tb) nor specific dynamic action could account for these high metabolic rates. Shrews died from heat stress after being exposed for 1 h to temperatures near 32 C. Metabolic rates increased at Ta's above 31.0 C in B. brevicauda, 34.0 C in C. gapperi, and 34.5 C in P. leucopus. Peromyscus leucopus copes with high temperatures better than shrews or voles. Peromyscus leucopus had lower Tb's at higher Ta's than shrews or voles, probably the result of a more effective heat loss mechanism requiring only a slight elevation of metabolism. This view is supported by the fact that there was a sharp increase in mg H₂O/cm³ O₂ at Ta's above 34 C in P. leucopus, but not in shrews or voles.