1. 1. The level and effectiveness of thermoregulation in bats is determined by the interaction of weight, basal rate of metabolism and thermal conductance. 2. 2. Conductances in tropical bats are greater than expected from weight. 3. 3. Basal rates of metabolism are higher than expected by weight in nectar-, fruit- and meat-eating bats, lower than expected in insectivorous species and intermediate in vampires, this correlation depending upon the seasonal stability of food resources in the environment. 4. 4. Therefore, nectar-, fruit- and meat-eating bats are effective thermoregulators, vampires are marginal regulators and insectivorous species readily enter torpor. 5. 5. Torpor evolved in the tropics in response to the high cost of thermoregulation at a small weight. © 1969.
