Meeting Abstract
Birds generate large amounts of heat during flight due to low mechanical efficiency of their flight muscles. At moderate temperatures hummingbirds dissipate excess heat generated during flight through heat dissipation areas (HDAs) around the eye, shoulder, and feet. However, because HDAs depend on thermal gradients they may be ineffective at higher temperature. Some birds with larger bills radiate heat from their bills as a supplemental form of heat dissipation; the bill is potentially ideal for convective heat dissipation during flight because it experiences high dynamic pressures In this study we used infrared thermography to determine if hummingbirds used their elongated bills for supplementary heat dissipation during flight, and if this might be a means of compensating for loss of a thermal gradient at high temperature. We measured variation in bill surface temperature of calliope hummingbirds (Selasphorus calliope; 2.5g) flown in a wind tunnel at 0-8 m/s (23°C) and 0 m/s (38°C) to determine if the bill could radiate heat. At both 23° C and 38°C bill surface temperature declined from the proximal to distal end of the bill. At 23°C the bird’s bill surface temperature was 3-7°C higher than that of ambient temperature, with highest temperatures near the proximal end of the bill. The favorable gradient thermal gradient between bill surface temperature and ambient temperature could indicate a thermoregulatory function for the bill at lower temperatures. At 38°C bill surface temperature did not differ from ambient temperature suggesting no thermoregulatory function at higher temperatures.
