Short-term energy conservation in endotherms in relation to body mass, habits, and environment

(1) The lower limit of thermoneutrality in some tropical, arboreal mammals that weigh over 2 kg is defined by a thermal conductance greater than the minimum. (2) The reduction in thermal conductance at low ambient temperatures is accomplished by peripheral vasoconstriction. (3) A similar reduction in thermal conductance is found in some birds, often at smaller masses than in mammals. (4) The combination of low conductances with low basal rates of metabolism facilitates energy conservation in species that have limited supplies of available energy. (5) The reduction of conductance at low ambient temperatures is one of the few physiological responses limited to intermediate body masses.