Avian thermoregulation in the heat: is evaporative cooling more economical in nocturnal birds?

Autor: O'Connor RS; 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., Smit B; Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown 6140, South Africa., Talbot WA; Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM 847131-0001, USA., Gerson AR; Department of Biology, University of Massachusetts, Amherst, MA 01003, USA., Brigham RM; Department of Biology, University of Regina, Regina, SK S4S 0A2, Canada., Wolf BO; Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM 847131-0001, USA., McKechnie AE; 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.; South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, P.O. Box 754, Pretoria 0001, South Africa.
Jazyk: angličtina
Zdroj: The Journal of experimental biology [J Exp Biol] 2018 Sep 06; Vol. 221 (Pt 17). Date of Electronic Publication: 2018 Sep 06.
DOI: 10.1242/jeb.181420
Abstrakt: Evaporative cooling is a prerequisite for avian occupancy of hot, arid environments, and is the only avenue of heat dissipation when air temperatures ( T a ) exceed body temperature ( T b ). Whereas diurnal birds can potentially rehydrate throughout the day, nocturnal species typically forgo drinking between sunrise and sunset. We hypothesized that nocturnal birds have evolved reduced rates of evaporative water loss (EWL) and more economical evaporative cooling mechanisms compared with diurnal species, permitting nocturnal species to tolerate extended periods of intense heat without becoming lethally dehydrated. We used phylogenetically informed regressions to compare EWL and evaporative cooling efficiency [ratio of evaporative heat loss (EHL) and metabolic heat production (MHP); EHL/MHP] among nocturnal and diurnal birds at high T a We analyzed variation in three response variables: (1) slope of EWL at T a between 40 and 46°C, (2) EWL at T a =46°C and (3) EHL/MHP at T a =46°C. Nocturnality emerged as a weak, negative predictor, with nocturnal species having slightly shallower slopes and reduced EWL compared with diurnal species of similar mass. In contrast, nocturnal activity was positively correlated with EHL/MHP, indicating a greater capacity for evaporative cooling in nocturnal birds. However, our analysis also revealed conspicuous differences among nocturnal taxa. Caprimulgids and Australian owlet-nightjars had shallower slopes and reduced EWL compared with similarly sized diurnal species, whereas owls had EWL rates comparable to those of diurnal species. Consequently, our results did not unequivocally demonstrate more economical cooling among nocturnal birds. Owls predominately select refugia with cooler microclimates, but the more frequent and intense heat waves forecast for the 21st century may increase microclimate temperatures and the necessity for active heat dissipation, potentially increasing owls' vulnerability to dehydration and hyperthermia.
Competing Interests: Competing interestsThe authors declare no competing or financial interests.
(© 2018. Published by The Company of Biologists Ltd.)
Databáze: MEDLINE
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