Tactics of heterothermy in eastern gray squirrels (Sciurus carolinensis)

Abstract

To investigate seasonal tactics of energy management, core body temperature (Tb) was monitored over 1 year in eastern gray squirrels (Sciurus carolinensis) maintained on a constant diet in an outdoor enclosure. Each fortnight, we recorded hourly temperatures via radio-telemetry on 2 separate days. We also measured Tb during 10-day periods of food deprivation in winter and summer. In comparison with summer and autumn values, Tb was 1-4°C lower at all times of the daily cycle throughout winter and spring. Night and morning Tb was reduced during food deprivation, and reductions during the winter deprivation (13°C) generally exceeded reductions during the summer deprivation (0-2°C). Maximum sustained Tb and activity levels occurred during late afternoon or early evening hours year-round, however, and Tb at this time of day during deprivations was indistinguishable from Tb under ad-lib feeding conditions in the same season. Seasonal change in Tb, including reduction in response to food deprivation, contributes to metabolic strategies employed by eastern gray squirrels, which resemble those of other tree squirrels. Further research on mechanisms of temperature adjustment, including photoperiodism, hormones, and shifting dietary preferences, would help to illuminate the evolution of metabolic strategies among Sciuridae and other mammals.