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Avian thermoregulation in the heat: is evaporative cooling more economical in nocturnal birds?
J Exp Biol 2018; 221(Pt 17)JE

Abstract

Evaporative cooling is a prerequisite for avian occupancy of hot, arid environments, and is the only avenue of heat dissipation when air temperatures (Ta) exceed body temperature (Tb). 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 Ta We analyzed variation in three response variables: (1) slope of EWL at Ta between 40 and 46°C, (2) EWL at Ta=46°C and (3) EHL/MHP at Ta=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.

Authors+Show Affiliations

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.Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown 6140, South Africa.Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM 847131-0001, USA.Department of Biology, University of Massachusetts, Amherst, MA 01003, USA.Department of Biology, University of Regina, Regina, SK S4S 0A2, Canada.Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM 847131-0001, USA.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.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

29950448

Citation

O'Connor, Ryan S., et al. "Avian Thermoregulation in the Heat: Is Evaporative Cooling More Economical in Nocturnal Birds?" The Journal of Experimental Biology, vol. 221, no. Pt 17, 2018.
O'Connor RS, Smit B, Talbot WA, et al. Avian thermoregulation in the heat: is evaporative cooling more economical in nocturnal birds? J Exp Biol. 2018;221(Pt 17).
O'Connor, R. S., Smit, B., Talbot, W. A., Gerson, A. R., Brigham, R. M., Wolf, B. O., & McKechnie, A. E. (2018). Avian thermoregulation in the heat: is evaporative cooling more economical in nocturnal birds? The Journal of Experimental Biology, 221(Pt 17), doi:10.1242/jeb.181420.
O'Connor RS, et al. Avian Thermoregulation in the Heat: Is Evaporative Cooling More Economical in Nocturnal Birds. J Exp Biol. 2018 09 6;221(Pt 17) PubMed PMID: 29950448.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Avian thermoregulation in the heat: is evaporative cooling more economical in nocturnal birds? AU - O'Connor,Ryan S, AU - Smit,Ben, AU - Talbot,William A, AU - Gerson,Alexander R, AU - Brigham,R Mark, AU - Wolf,Blair O, AU - McKechnie,Andrew E, Y1 - 2018/09/06/ PY - 2018/04/17/received PY - 2018/06/14/accepted PY - 2018/6/29/pubmed PY - 2019/10/15/medline PY - 2018/6/29/entrez KW - Caprimulgiformes KW - Dehydration tolerance KW - Diurnal KW - Evaporative water loss KW - Heat tolerance KW - Strigiformes JF - The Journal of experimental biology JO - J. Exp. Biol. VL - 221 IS - Pt 17 N2 - Evaporative cooling is a prerequisite for avian occupancy of hot, arid environments, and is the only avenue of heat dissipation when air temperatures (Ta) exceed body temperature (Tb). 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 Ta We analyzed variation in three response variables: (1) slope of EWL at Ta between 40 and 46°C, (2) EWL at Ta=46°C and (3) EHL/MHP at Ta=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. SN - 1477-9145 UR - https://www.unboundmedicine.com/medline/citation/29950448/Avian_thermoregulation_in_the_heat:_is_evaporative_cooling_more_economical_in_nocturnal_birds L2 - http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=29950448 DB - PRIME DP - Unbound Medicine ER -