A New Function for Torpor: Fat Conservation in a Wild Migrant Hummingbird

Abstract

Laboratory studies of torpor in small endotherms suggest that body temperature is lowered periodically only when the animal is energetically stressed. Almost no data exist on the use and importance of torpor outside laboratory situations. We have monitored the daily energy state of hummingbirds in the field. A rare observation of a torpid individual whose energy state and ecological situation were well-documented showed that migrant hummingbirds may use torpor when they are very fat and not presently energetically stressed. In this case, torpor may be a mechanism to conserve the energy stored for later use on migration.