Meeting Abstract
Hummingbirds generate large amounts of heat during hovering. When ambient temperatures (Ta) are cool this extra heat could be used as a source of endogenous heat to maintain body temperature. However, when Ta is warm this extra heat must be dissipated to avoid hyperthermia. Our previous work suggests that hummingbirds have difficulty dissipating heat while hovering in warm Ta likely requiring them to behaviorally thermoregulate after perching. In this study we used infrared thermography and standard video recordings to examine differences in heat retention/dissipation strategies between hovering and perching calliope hummingbirds (Selasphorus calliope, ~2.5 g) at 5, 22, and 32 °C. Based on earlier anecdotal observations we predicted that perching birds would rapidly radiate heat from the flight muscles after hovering. However, this was not supported by our data. Instead across all Ta values regulation of heat delivery to the bill, feet, and eye heat dissipation area (HDA) appeared key in controlling heat transfer during both hovering and perching. At 5 °C no heat was actively delivered to either the bill or feet when hovering or perching allowing for effective heat retention. At 32 °C the bill and feet appeared actively warmed with surface temperatures (Ts) sometimes >40 °C during hovering. Ts variation of the eye HDA was less than for the bill and feet but exhibited slightly higher Ts during hovering when heat transfer across general body surfaces is limited. While calliope hummingbirds can effectively cool while perching higher Ts of bill, feet, and eye HDA exhibited during hovering result in thermal gradients of 8-10 °C promoting dissipation of some of the heat produced during hovering even when Ta is warm.
