On Estimating Thermal Conductance in Endotherms

Abstract

Thermal conductance is a measure of the ease with which heat is exchanged between a body and the environment. It may include or exclude evaporative heat loss. If evaporative heat loss is included, conductance in endotherms should be used only at temperatures below thermoneutrality because evaporation is of little importance only at these temperatures. The slope of the curve of metabolism on air temperature equals conductance if and only if the curve extrapolates to body temperature when the rate of metabolism is zero. Slopes fitted by the method of least squares ( ) usually are less than the mean minimal conductance ( ) calculated from individual measurements of metabolism below thermoneutrality, because most endotherms mix physical and chemical thermoregulation at temperatures below thermoneutrality. The extent to which an extrapolation of the fitted curve overestimates body temperature (δT) is related to the error by which fitted slopes estimate mean minimal conductance: . This relation can be used to correct fitted slopes in the literature to mean minimal conductances, as long as the mean air temperature at which minimal conductance is being estimated falls between 12 and 20 C and mean body temperature falls between 32 and 38 C.