Avian thermoregulation in the heat: phylogenetic variation among avian orders in evaporative cooling capacity and heat tolerance

• DOI: 10.1242/jeb.174870
• Publication Date: 2018-02-14T01:11:05Z
• Authors: Ben Smit; Maxine C. Whitfield; William A. Talbot; Alexander R. Gerson; Andrew E. McKechnie; Blair O. Wolf
• Keywords: Evaporative cooler

Little is known about the phylogenetic variation of avian evaporative cooling efficiency and heat tolerance in hot environments. We quantified thermoregulatory responses to high air temperature (Ta) ∼100-g representatives three orders, namely, African cuckoo (Cuculus gularis, Cuculiformes), lilac-breasted roller (Coracias caudatus, Coraciiformes) Burchell's starling (Lamprotornis australis, Passeriformes). All species initiated respiratory mechanisms increase dissipation when body (Tb) approached 41.5°C response increasing Ta, with gular flutter observed cuckoos panting rollers starlings. Resting metabolic rate water loss increased by quantitatively similar magnitudes all species, although maximum rates were proportionately lower Evaporative [defined as ratio (EHL) production (MHP)] generally remained below 2.0 starlings, but reached a ∼3.5 rollers. The value for reveals very efficient mechanism, EHL/MHP maxima similarly sized columbids which effectively dissipate via cutaneous evaporation. This unexpected among orders tested physiological an important step toward determining evolution traits desert birds.