Meeting Abstract
Birds must dissipate large amounts of heat produced during flight. In forward flight this is a challenge because the skin is insulated by plumage that must stay aerodynamic. In passerines heat dissipation occurs where feather density is low (head, axial, and legs). To place these data in a comparative context, we analyzed surface-heat dissipation in hummingbirds flying at 0-12 m/s. Hummingbirds are unique in that they are capable of sustained hovering, yet also capable of speeds to >12 m/s including transition from limited convection during hovering to high convection in forward flight. We measured surface temperature (Ts) in hummingbirds both in a wind tunnel (0-12 m/s) and in the field using infrared thermography. Important regions of heat dissipation were the head/eye, axial, and legs/feet. Mean body Ts was highest during hovering. Mean Ts of the eye was constant across speeds, but decreased in size with notable transitions at 2, 8, and 12 m/s as convection increased. Heat dissipation through the legs/feet occurred during hovering, but only rarely during forward flight. Both the head/eye and legs/feet appear important when convection is low. The eye is located at what is likely an area of peak dynamic pressure, ideally placed for facilitating convection at all speeds. In free-living hummingbirds Ts increases linearly with environmental temperature. Because temperature is predicted to increase due to climate change in many hummingbird habitats it is possible that smaller thermal gradients will make heat dissipation during hovering more difficult and contribute to climate-change related shifts in distribution. Supported by NSF grants IOS-0923606 and IOS-0919799, and NASA 10-BIOCLIM10-009.
