Avian thermoregulation in the heat: evaporative cooling in five Australian passerines reveals within-order biogeographic variation in heat tolerance

• DOI: 10.1242/jeb.155507
• Publication Date: 2017-04-29T00:30:23Z
• Authors: Andrew E. McKechnie; Alexander R. Gerson; Todd J. McWhorter; Eric Krabbe Smith; William A. Talbot; Blair O. Wolf
• Keywords: Evaporative cooler; Respirometry

Evaporative heat loss pathways vary among avian orders, but the extent to which evaporative cooling capacity and tolerance varies within orders remains unclear. We quantified upper limits thermoregulation under extremely hot conditions in five Australian passerines: yellow-plumed honeyeater (Lichenostomus ornatus; ∼17 g), spiny-cheeked (Acanthagenys rufogularis; ∼42 chestnut-crowned babbler (Pomatostomus ruficeps; ∼52 grey butcherbird (Cracticus torquatus; ∼86 g) apostlebird (Struthidea cinerea; ∼118 g). At air temperatures (Ta) exceeding body temperature (Tb), all species showed increases Tb maximum values around 44 – 45 °C, accompanied by rapid resting metabolic rate above clearly defined critical of thermoneutrality water (EWL) levels equivalent 670 860 % baseline rates at thermoneutral Ta. Maximum capacity, as fraction production dissipated evaporatively, ranged from 1.20 2.17, consistent with known range for passerines, well below corresponding ranges columbids caprimulgids. Heat (HTL, Ta tolerated) scaled positively mass, varying 48 °C honeyeaters 52 apostlebirds, were lower than those three southern African ploceid passerines investigated previously. argue this difference is functionally linked a smaller scope EWL levels. Our data reiterate reliance general on respiratory via panting, also reveal substantial within-order variation capacity.