ABSTRACT
One of the characteristics of birds and mammals is their ability to adjust their metabolism and thereby maintain relatively high and constant body temperatures over a wide range of thermal conditions in the environment. This chapter describes avian torpor from an energetic perspective. The use of shallow hypothermia in response to immediate energetic emergencies is contrasted initially with the use of torpor to preserve abundant energy supplies. Hibernation is a seasonal dormancy that differs from daily torpor in that animals remain in one location for a prolonged period without foraging. The use of daily torpor during the active season is greatly limited in desert-dwelling poorwills, presumably because cool temperatures are rare at that time. Poorwills, like migrating hummingbirds, use daily torpor in the autumn to maintain abundant fat reserves. Poorwills are remarkably impervious to disturbances once they have settled into hibernation.
