Energetic costs of the winter arboreal microclimate: The gray squirrel in a tree

Abstract

Heated taxidermic mounts of the gray squirrel were used to analyze the thermal environment of a small arboreal endotherm. Changes in the standard operative temperature (Tes) calculated from the temperatures of heated and unheated mounts agreed well with the power consumption (M−E) of mounts on the ground and on the wind-ward side of a 48-cm diameter tree trunk. As wind speed (u) rose and sky solar radiation (Qr) decreased, the windward side of the tree trunk became an increasingly more stressful thermal environment than the leeward side of the trunk or the ground, producingM−E differences of more than 30%. Although theM−E of a ground mount and a limb mount 4 m in the air are dependent onQras well asu, the ratio of the two value ofM−E is independent ofQr, poorly predicted byu and well predicted byu1/2.