Meeting Abstract
Flying animals generate large amounts of heat, which must be dissipated to avoid overheating. In birds, heat dissipation during flight is retarded by feathers, which cover most body surfaces. Heat dissipation is critical for hummingbirds who generate enormous mass-specific power during hovering. At moderate temperature (21°C) the thermal gradient allows hummingbirds to dissipate excess heat using heat dissipation areas around the eye, shoulder, and legs where feather density is reduced. However, predicted increases in environmental temperature resulting from climate change could decrease the thermal gradient needed for passive heat loss forcing reliance only on evaporation. In this study we used infrared thermography to measure surface temperature in hummingbirds at temperatures ranging from 15-48 °C to test how high environmental temperature impacts passive heat dissipation during hovering. Average body surface temperature positively correlated with environmental temperature from 15-38°C (environmentally controlled), but became constant at > 38 °C suggesting behavioral thermoregulation. Mean surface temperature of heat dissipation areas remained constant (~33°C) between 15-42°C suggesting integration with the body core. Thus, as environmental temperature increases, the thermal gradient for passive heat transfer decreases. When environmental temperature exceeds ~39°C the thermal gradient was reversed, causing an increase in thermal load. Predicted higher temperatures due to climate change could increase the risk of overheating during flight, thereby causing changes in foraging behavior and important social activities.
