Comparative energetics of coat colour polymorphs in the eastern grey squirrel, Sciurus carolinensis

Heat loss at various environmental temperatures was examined in colour morphs of the eastern grey squirrel, Sciurus carolinensis, during summer and winter.In winter pelage, melanistic squirrels had significantly (p < 0.05) lower heat losses and lower basal metabolic rates than grey morphs at ambient temperatures between −20 and 25 °C. No such differences were observed between colour morphs in summer pelage.Thermal conductances were significantly higher in summer animals. However, there were no significant differences in conductance associated with pelage colouration in either summer or winter squirrels.Melanistic S. carolinensis thus appear to have a lower energy cost for existence during winter than do grey morphs. This may contribute to the apparent superior fitness of melanistic morphs in the northern portion of the species' range. Lower heat loss by melanistic squirrels during winter, without a concomitant reduction in thermal conductance, may be associated with a lower body core temperature.