Avian thermoregulation in the heat: evaporative cooling capacity and thermal tolerance in two Australian parrots

• DOI: 10.1242/jeb.168930
• Publication Date: 2018-02-14T01:11:05Z
• Authors: Todd J. McWhorter; Alexander R. Gerson; William A. Talbot; Eric Krabbe Smith; Andrew E. McKechnie; Blair O. Wolf
• Keywords: Evaporative cooler; Hot weather; Operative temperature

Avian orders differ in their thermoregulatory capabilities and tolerance of high environmental temperatures. Evaporative heat loss, the primary avenue whereby it occurs, differs amongst taxa. Although Australian parrots (Psittaciformes) have been impacted by mass mortality events associated with extreme weather (heat waves), physiology has not well-characterized. We quantified upper limits to thermoregulation under extremely hot conditions two parrots: mulga parrot (Psephotellus varius; ∼55 g) galah (Eolophus roseicapilla; ∼265 g). At air temperatures (Ta) exceeding body temperature (Tb), both species showed increases Tb maximum values around 43–44°C, accompanied rapid resting metabolic rate above clearly defined critical thermoneutrality evaporative water loss (EWL) levels equivalent 700–1000% baseline rates at thermoneutral Ta. Maximum cooling capacity, as fraction production dissipated evaporatively, ranged from 1.71 1.79, consistent known range for parrots, similar corresponding passerines, well below ranges columbids caprimulgids. Heat limit (HTL, Ta tolerated) 44-55°C, reported but lower than Our data suggest that is passerines. argue understanding how capacity vary across avian vital predicting climate change increase frequency may impact populations future.