Meeting Abstract
The low mechanical efficiency of hummingbird flight muscles results in the production of large amounts of endogenous heat during hovering. Dissipation of this extra heat is necessary to avoid hyperthermia but is confined to specific heat dissipation areas (HDAs) around the eyes, legs/feet, and the axial region due to insulation by the body contour feathers. However, when ambient temperature (Ta) is warm hummingbirds appear unable to sufficiently increase evaporation to compensate for the loss of passive heat dissipation. Thus, it is likely that when Ta is warm hummingbirds depend on intermittent behavioral thermoregulation while perching to manage body temperature. In this study we used infrared thermography and standard video recordings to examine heat dissipation in perching hummingbirds following hovering bouts. We also offered hummingbirds a choice between warm (Ta =20-37°C) and artificially cooled perches to see if microclimate was important for perch selection. Data were collected on 3 hummingbird species (Archilochus alexandri, Eugenes fulgens, and Lampornis clemenciae) ranging in mass from 2.8-9.6 g. As Ta increased breast surface temperature (Ts) exceeded mean total body Ts across all Ta values suggesting some accumulated heat is escaping through breast plumage. At the warmest Ta (37°C) breast Ts could be up to 42°C. Interestingly even at our warmest Ta mean head Ts never exceeded 40°C even when the Ts of other body surfaces was higher perhaps to protect the brain. Both the bill and feet were important means of heat dissipation. When at Ta >34°C heat was actively delivered to both bill and feet, and at the warmest Ta their Ts could be as high as 42°C perhaps suggesting slight hyperthermia during hovering. Our data suggest that these physiological mechanisms for dissipating heat are more important than microclimate selection.
