TORPOR IN 3 SPECIES OF BRAZILIAN HUMMINGBIRDS UNDER SEMINATURAL CONDITIONS

We measured body temperatures in three species of Brazilian hummingbir ds, the Versicolored Emerald (Amazilia versicolor; body mass 4.1 g), t he Black Jacobin (Me lantrochilus fuscus; body mass 7.7 g) and the Swa llow-tailed Hummingbird (Eupetomena macroura; body mass 8.6 g), during overnight exposure to natural conditions of photoperiod and ambient t emperatures. All three species entered torpor. In both A. versicolor a nd E. macroura, individuals entered torpor even if they had access to feeders up to the time of sunset. In contrast, M. fuscus was less pron e to enter torpor and did so mainly if it had been fasting for more th an two hours before sunset. Furthermore, M. fuscus often spent the who le night in torpor, whereas the two other species entered torpor for a variable, often short, period of the night. We observed more than one torpor bout during a single night in all three species. We suggest th at multiple nocturnal torpors result from interruption of the normal t orpor pattern by some (unknown) external stimuli. Any interrupted torp or was always followed by a new entry into torpor, supporting the view that there is a body mass threshold below which the hummingbirds must enter torpor Our data also indicate that these hummingbird species mi ght use torpor even if they are not energetically stressed.