Meeting Abstract
Hovering flight is used frequently by hummingbirds during foraging to meet fuel energy demands. Hovering is not only energy expensive, but heat generated by flight muscles imposes a thermoregulatory challenge. To dissipate excess heat birds rely on evaporation, conduction, and induced convection (caused by wing movement), of which the latter two depend on a thermal gradient. Increased temperature due to climate change might reduce this thermal gradient, making heat dissipation more difficult, causing heat management to be more challenging. To understand how body size and ambient temperature (Ta) impact heat dissipation in hovering hummingbirds we used infrared thermography to measure surface temperature (Ts) in 5 hummingbird species ranging in size from 2.8-8.0g over Ta ranging from18-29°C during hovering flight. Consistent with previous studies mean body Ts was relatively low (25-30 °C) as plumage insulates the skin surface, with heat dissipation occurring primarily from regions around the eye, axial, and legs/feet where feather density is low. Except for the use of legs/feet, mean and maximum Ts, and relative size of heat dissipation regions did not vary with body size suggesting that heat dissipation strategies were similar for all species. Smaller species (<3.5 g) dangled their feet while hovering whereas feet remained tucked in larger species (7.5-8.0 g). It is not clear why heat dissipation from legs/feet is less important for larger species. Except for mean body Ta, all mean and maximum Ta values were positively correlated with Ta suggesting that environmental temperature can reduce the thermal gradient. The size of heat dissipation areas was not correlated with Ta and is perhaps restricted more by feather density.
