Meeting Abstract
P3-131 - Use of the Bill as a Heat Radiator by Anna hummingbirds, Calypte anna Smith, AE*; Tobalske, BW; Lapsansky, AB; Powers, DR; George Fox University, Newberg, OR; University of Montana, Missoula, MT; University of Montana, Missoula, MT; George Fox University, Newberg, OR asmith18@georgefox.edu http://www.dpowerslab.com
Hummingbirds are small endotherms that could find maintaining body temperature (Tb) difficult as environmental temperatures climb due to climate change. Maintaining Tb is particularly difficult during flight because they produce large amounts of endogenous heat due to flight muscle inefficiency. Plumage acts as an insulating layer, thus requiring most heat loss to occur across areas with little to no feather coverage (i.e. heat dissipation areas, HDAs). Heat is passively shed from HDAs to the environment when there is a favorable thermal gradient. Creating a thermal gradient becomes increasingly difficult at high ambient temperature (Ta). To enhance passive heat dissipation birds increase blood flow to their bill to raise surface temperature (Ts) which increases radiative heat loss. To investigate the role the bill plays in heat dissipation strategies of Anna hummingbirds (Calypte anna, 4.5g), we simultaneously measured hovering metabolic rate (HMR) using open-flow mask respirometry, and bill Ts, using infrared thermography, at moderate (20°C) and high Ta (35°C). HMR ranged from 1.0-1.9W and did not vary between temperatures. Interestingly, bill radiation accounted for dissipation of only ~2.5% of metabolic heat at both temperatures. Even so, bills were actively heated 60% more frequently at 35°C reaching mean Ts of 39°C. At 35°C radiating heat from the bill might be insufficient to maintain Tb as some hummingbirds enhanced heat dissipation by panting to increase respiratory evaporative water loss. It is possible bill heat radiation is more important for regulating internal head temperature (which never exceeded 40°C) than for maintenance of overall core Tb.