Avian thermoregulation in the heat: evaporative cooling capacity of arid-zone caprimulgiforms from two continents

• DOI: 10.1242/jeb.161653
• Publication Date: 2017-08-01T00:10:22Z
• Authors: William A. Talbot; Todd J. McWhorter; Alexander R. Gerson; Andrew E. McKechnie; Blair O. Wolf
• Keywords: Plumage; Homeothermy; Evaporative cooler

Birds in the order Caprimulgiformes (nightjars and allies) have a remarkable capacity for thermoregulation over wide range of environmental temperatures, exhibiting pronounced heterothermy cool conditions extreme heat tolerance at high temperatures. We measured thermoregulatory responses to acute stress three species caprimulgiforms that nest areas aridity, common poorwill (Phalaenoptilus nuttallii: Caprimulgidae) lesser nighthawk (Chordeiles acutipennis: Sonoran Desert Arizona, Australian owlet-nightjar (Aegotheles cristatus: Aegothelidae) mallee woodlands South Australia. exposed wild-caught birds progressively increasing air temperatures (Ta) resting metabolic rates (RMR), evaporative water loss (EWL), body temperature (Tb) limits (HTL; maximum Ta reached). Comparatively low RMR values were observed all (0.35 W, 0.36 W 0.40 poorwill, owlet-nightjar, respectively), with Tb approximating 40°C mild hyperthermia occurring as reached HTL. Nighthawks poorwills HTLs 60 62°C, respectively, whereas had an HTL 52°C. increased gradually above minima Tas 42, 42 35°C, 1.7, 1.9, 2.0 X minimum nighthawk, respectively. EWL rapidly linearly exceeded resulted dissipation equivalent 237-424% production. Bouts gular flutter large transient increases (50-123 %) accompanied by only small increments (<5%). The cavity-nesting/roosting lower less efficient cooling compared and/or roost on open desert surfaces. efficiency cooling, combined hyperthermia, provide physiological basis defending well below is comparable arid-zone columbids which cutaneous predominant pathway.