Meeting Abstract
P2-94 - Radiative Heat Management by Free-Living Hovering Hummingbirds Regier, TM*; Dobbyn, WR; Tobalske, BW; Powers, DR; George Fox University, Newberg, OR; George Fox University, Newberg, OR; University of Montana, Missoula, MT; George Fox University, Newberg, OR tregier18@georgefox.edu http://www.dpowerslab.com
During hovering excess endogenous heat is generated by inefficient flight muscles that must be dissipated to manage heat balance. Body temperature (Tb) regulation while hovering can be difficult because plumage insulates body surfaces restricting heat loss to heat dissipation areas (HDAs) around the bill, hindlimbs, and eye. These HDAs are important at cooler ambient temperatures (Ta) but at high Ta hummingbirds lose the thermal gradient for passive heat dissipation and must rely on evaporative heat loss. In laboratory studies, captive hovering hummingbirds increase blood circulation from their central core to heat both their bill and legs/feet to create favorable thermal gradients for passive heat dissipation even at higher Ta. Laboratory measurements are controlled and do not account for all environmental factors such as wind, humidity, and solar radiation. Thus, it is unclear if heating of the bill and legs/feet are an effective heat dissipation strategy for free-living hummingbirds. In this study we used infrared thermography to track management of thermal gradients on the body surface of free-living Anna’s hummingbirds (Calypte anna, 4.5 g) to test if they actively heat their bill and hindlimbs across Ta ranging from 18-40 °C in a manner similar to what is observed in the lab. At Ta = 30-40°C Anna’s appear to actively heat their bills and hindlimbs consistently resulting in mean Ts that can be >40°C. There was also no difference in Ts measurement between birds measured during full sun exposure and those measured when shaded. At Ta = 18-29 °C both the bill and hindlimbs appeared to heat when measured in full sun exposure with Ts >35°C, but they did not appear routinely heated when measured in the shade with mean Ts ~ 23°C. This suggests that radiative heat gain by surfaces of the bill and hindlimbs when exposed to direct sunlight might make use of these areas for thermoregulation in a manner more complex than what occurs in simplified conditions in the lab.