Energetics and the Distribution of Vampires

Abstract

The weight fluctuations and rates of metabolism of vampires in the laboratory were examined in an attempt to describe the energy budget of vampires in the field. Their energy expenditure is limited by the size of the meal that can be transported in flight. A Desmodus of 42 grams would expend about 26 kilocalories per day, more than 90 per cent of which is committed directly to homeostasis and to the cost of handling the food. Appreciably colder environmental temperatures than those found in the tropics would increase the cost of thermoregulation, which in turn would require a meal-size beyond that which can be transported. In fact, the limits in distribution of Desmodus are correlated with the 10°C minimal winter isotherm both in Mexico and in Argentina and Chile.