Meeting Abstract
Hummingbirds generate a large amount of heat during flight due to the low mechanical efficiency of their flight muscles and they must dissipate that heat to avoid overheating. Heat can be dissipated passively (convection, conduction, and radiation) and by evaporation (respiratory and cutaneous). When environmental temperatures are high, passive heat dissipation is eliminated leaving evaporation as the only option for thermoregulation. In hummingbirds, respiratory evaporation accounts for < 40% of metabolic heat production, requiring the balance of metabolic heat production to be dissipated by cutaneous evaporation. Aerodynamically positioned feathers restrict passive heat dissipation during flight, but it is unknown if cutaneous evaporation will be affected as well. We studied evaporative heat dissipation at temperatures near the limits for passive heat dissipation in hovering calliope (Selasphorus calliope), Rivoli’s (Eugenes fulgens), and black-chinned (Archilocus alexandri) hummingbirds using open-flow respirometry and video recordings. Cutaneous evaporation was estimated as total evaporation minus respiratory evaporation. Our measurements in calliope hummingbirds suggest that they are unable to sufficiently upregulate cutaneous evaporative water loss to compensate for the extra heat produced during hovering. Observations of all species studied suggest that post-hovering behaviors might be important for rapidly dumping heat following a hovering bout in warm conditions.
