Meeting Abstract
P2-93 - Effectiveness of passive heat dissipation in free-living Anna’s hummingbirds (Calypte anna) at moderate and high ambient temperature Dobbyn, WR*; Regier, TM; Tobalske, BW; Powers, DR; George Fox University, Newberg, OR; George Fox University, Newberg, OR; University of Montana, Missoula, MT; George Fox University, Newberg, OR wdobbyn19@georgefox.edu http://www.dpowerslab.com
Thermoregulation is a large portion of daily energy expenditure in endothermic animals due to the high cost of the maintenance of body temperature (Tb). At temperature extremes endotherms often exhibit adaptations that reduce thermoregulatory costs, making it easier to balance daily energy costs. Anna’s hummingbird (Calypte anna, 4.5 g), a non-migratory species with a rapidly expanding range, have established populations in western North America that require tolerance of extreme hot and cold conditions. We are interested in testing if the rapid range expansion is in part due to adaptations allowing effective thermoregulation over a range of temperatures. We report data on passive heat dissipation in free-living Anna’s at ambient temperatures (Ta) from 16-40 °C. We used infrared thermography to measure surface temperatures (Ts) in free-living Anna’s to assess passive heat dissipation by quantifying thermal gradients and measuring heating of the bill and hindlimbs. The legs/feet maintained a 3°C thermal gradient across all temperatures. Additionally, birds fully extend their legs as Ta increases, increasing surface area for passive heat dissipation. In contrast, the thermal gradient of the bill declined with increasing Ta from 5°C at Ta=18 to 1.0°C at Ta=40°C. These data are driven by Anna’s ability to actively heat the bill and hindlimbs to a Ts>Ta. Reduced thermal gradients of the bill at higher Ta might be due to limitations in Anna’s ability to heat the bill. The bill’s primary role might be to regulate head temperature where Ts never exceeds 40 °C. These data show that Anna’s uses both behavioral and physiological strategies to adjust passive heat dissipation across a range of Ta. These strategies, along with evaporative heat dissipation, such as increased panting when Ta is high, could contribute to Anna’s success in a wide range of habitats.