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Avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern African arid-zone passerines.
J Exp Biol 2015; 218(Pt 11):1705-14JE

Abstract

Many birds can defend body temperature (Tb) far below air temperature (Ta) during acute heat exposure, but relatively little is known about how avian heat tolerance and evaporative cooling capacity varies with body mass (Mb), phylogeny or ecological factors. We determined maximum rates of evaporative heat dissipation and thermal end points (Tb and Ta associated with thermoregulatory failure) in three southern African ploceid passerines, the scaly-feathered weaver (Sporopipes squamifrons, Mb≈10 g), sociable weaver (Philetairus socius, Mb≈25 g) and white-browed sparrow-weaver (Plocepasser mahali, Mb≈40 g). Birds were exposed to a ramped profile of progressively increasing Ta, with continuous monitoring of behaviour and Tb used to identify the onset of severe hyperthermia. The maximum Ta birds tolerated ranged from 48°C to 54°C, and was positively related to Mb. Values of Tb associated with severe heat stress were in the range of 44 to 45°C. Rates of evaporative water loss (EWL) increased rapidly when Ta exceeded Tb, and maximum evaporative heat dissipation was equivalent to 141-222% of metabolic heat production. Fractional increases in EWL between Ta<40°C and the highest Ta reached by each species were 10.8 (S. squamifrons), 18.4 (P. socius) and 16.0 (P. mahali). Resting metabolic rates increased more gradually with Ta than expected, probably reflecting the very low chamber humidity values we maintained. Our data suggest that, within a taxon, larger species can tolerate higher Ta during acute heat stress.

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, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031, South Africa.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.UNM Biology Department, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA.

Pub Type(s)

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

Language

eng

PubMed ID

26041032

Citation

Whitfield, Maxine C., et al. "Avian Thermoregulation in the Heat: Scaling of Heat Tolerance and Evaporative Cooling Capacity in Three Southern African Arid-zone Passerines." The Journal of Experimental Biology, vol. 218, no. Pt 11, 2015, pp. 1705-14.
Whitfield MC, Smit B, McKechnie AE, et al. Avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern African arid-zone passerines. J Exp Biol. 2015;218(Pt 11):1705-14.
Whitfield, M. C., Smit, B., McKechnie, A. E., & Wolf, B. O. (2015). Avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern African arid-zone passerines. The Journal of Experimental Biology, 218(Pt 11), pp. 1705-14. doi:10.1242/jeb.121749.
Whitfield MC, et al. Avian Thermoregulation in the Heat: Scaling of Heat Tolerance and Evaporative Cooling Capacity in Three Southern African Arid-zone Passerines. J Exp Biol. 2015;218(Pt 11):1705-14. PubMed PMID: 26041032.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern African arid-zone passerines. AU - Whitfield,Maxine C, AU - Smit,Ben, AU - McKechnie,Andrew E, AU - Wolf,Blair O, PY - 2015/6/5/entrez PY - 2015/6/5/pubmed PY - 2016/6/15/medline KW - Body temperature KW - Critical thermal maximum KW - Evaporative water loss KW - Hyperthermia KW - Metabolic rate KW - Upper critical limit of thermoneutrality SP - 1705 EP - 14 JF - The Journal of experimental biology JO - J. Exp. Biol. VL - 218 IS - Pt 11 N2 - Many birds can defend body temperature (Tb) far below air temperature (Ta) during acute heat exposure, but relatively little is known about how avian heat tolerance and evaporative cooling capacity varies with body mass (Mb), phylogeny or ecological factors. We determined maximum rates of evaporative heat dissipation and thermal end points (Tb and Ta associated with thermoregulatory failure) in three southern African ploceid passerines, the scaly-feathered weaver (Sporopipes squamifrons, Mb≈10 g), sociable weaver (Philetairus socius, Mb≈25 g) and white-browed sparrow-weaver (Plocepasser mahali, Mb≈40 g). Birds were exposed to a ramped profile of progressively increasing Ta, with continuous monitoring of behaviour and Tb used to identify the onset of severe hyperthermia. The maximum Ta birds tolerated ranged from 48°C to 54°C, and was positively related to Mb. Values of Tb associated with severe heat stress were in the range of 44 to 45°C. Rates of evaporative water loss (EWL) increased rapidly when Ta exceeded Tb, and maximum evaporative heat dissipation was equivalent to 141-222% of metabolic heat production. Fractional increases in EWL between Ta<40°C and the highest Ta reached by each species were 10.8 (S. squamifrons), 18.4 (P. socius) and 16.0 (P. mahali). Resting metabolic rates increased more gradually with Ta than expected, probably reflecting the very low chamber humidity values we maintained. Our data suggest that, within a taxon, larger species can tolerate higher Ta during acute heat stress. SN - 1477-9145 UR - https://www.unboundmedicine.com/medline/citation/26041032/Avian_thermoregulation_in_the_heat:_scaling_of_heat_tolerance_and_evaporative_cooling_capacity_in_three_southern_African_arid_zone_passerines_ L2 - http://jeb.biologists.org/cgi/pmidlookup?view=long&amp;pmid=26041032 DB - PRIME DP - Unbound Medicine ER -