title: Avian thermoregulation in the heat: efficient evaporative cooling allows for extreme heat tolerance in four southern hemisphere columbids.
abstract: Birds show phylogenetic variation in the relative importance of respiratory versus cutaneous evaporation, but the consequences for heat tolerance and evaporative cooling capacity remain unclear. We measured evaporative water loss (EWL), resting metabolic rate (RMR) and body temperature (Tb) in four arid-zone columbids from southern Africa [Namaqua dove (Oena capensis, ∼37 g), laughing dove (Spilopelia senegalensis, ∼89 g) and Cape turtle dove (Streptopelia capicola, ∼148 g)] and Australia [crested pigeon (Ocyphaps lophotes), ∼186 g] at air temperatures (Ta) of up to 62°C. There was no clear relationship between body mass and maximum Ta tolerated during acute heat exposure. Maximum Tb at very high Ta was 43.1±1.0, 43.7±0.8, 44.7±0.3 and 44.3±0.8°C in Namaqua doves, laughing doves, Cape turtle doves and crested pigeons, respectively. In all four species, RMR increased significantly at Ta above thermoneutrality, but the increases were relatively modest with RMR at Ta=56°C being 32, 60, 99 and 11% higher, respectively, than at Ta=35°C. At the highest Ta values reached, evaporative heat loss was equivalent to 466, 227, 230 and 275% of metabolic heat production. The maximum ratio of evaporative heat loss to metabolic production observed in Namaqua doves, 4.66, exceeds by a substantial margin previous values reported for birds. Our results support the notion that cutaneous evaporation provides a highly efficient mechanism of heat dissipation and an enhanced ability to tolerate extremely high Ta.
authors.affiliation: DST-NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa aemckechnie@zoology.up.ac.za.
authors.forename: Andrew E
authors.identifier: 0000-0002-1524-1021
authors.initials: AE
authors.lastname: McKechnie
authors.affiliation: DST-NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.
authors.forename: Maxine C
authors.initials: MC
authors.lastname: Whitfield
authors.affiliation: Department of Zoology, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031, South Africa.
authors.forename: Ben
authors.initials: B
authors.lastname: Smit
authors.affiliation: Department of Biology, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Gerson
authors.affiliation: UNM Biology Department, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA.
authors.forename: Eric Krabbe
authors.initials: EK
authors.lastname: Smith
authors.affiliation: UNM Biology Department, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Talbot
authors.affiliation: School of Animal & Veterinary Sciences, University of Adelaide, Roseworthy Campus, SA 5371, Australia.
authors.forename: Todd J
authors.initials: TJ
authors.lastname: McWhorter
authors.affiliation: UNM Biology Department, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA.
authors.forename: Blair O
authors.initials: BO
authors.lastname: Wolf
mesh_terms: D000388:Air; D000818:Animals; D001315:Australia; D001481:Basal Metabolism / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D010856:Columbidae / Q000502:physiology*; D006358:Hot Temperature; D013019:South Africa; D000071436:Thermotolerance / Q000502:physiology*; D014870:Water Loss, Insensible / Q000502:physiology*
keywords: Body temperature; Columbiformes; Cutaneous evaporative water loss; Hyperthermia; Passeriformes; Respiratory evaporative water loss