Meeting Abstract
As global temperatures increase, hummingbirds must be able to dissipate excess heat produced during flight to avoid hyperthermia. 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. The heat dissipation area surrounding the eye is particularly important because of high near-field flow velocities generated around the head. In this study we made near-field measurements of surface temperature around the eye of calliope hummingbirds (Selasphorus calliope; ~2.7 g) to look for evidence of physiological regulation of heat delivery in response to increased heat production during flight. Average surface temperature of the heat dissipation area was 30.3°C, and did not vary with flight speed. During hovering, the maximum surface temperature increased by 0.2 °C during an ~8 second interval. At flight speeds of 4 and 8 m/s, the maximum surface temperature decreased by 0.1-0.2°C due to increased convection. At 8 m/s maximum surface temperature decreased 0.6 °C, and size of the heat dissipation area decreased by 33%. The small increase in maximum surface temperature during hovering might indicate increased heat delivery to the skin surface. Any evidence of increased heat delivery during forward flight is likely masked by increased convection.
