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Interactions between humidity and evaporative heat dissipation in a passerine bird.
J Comp Physiol B. 2019 04; 189(2):299-308.JC

Abstract

Environmental humidity is thought to be a major determinant of evaporative cooling capacity at high air temperatures (Ta), but the technical challenges of experimentally manipulating humidity in respirometry chambers have resulted in far less being known about the effects of humidity compared to those of Ta. We tested the prediction that at Ta approaching and exceeding normothermic body temperature (Tb), high humidity would result in higher Tb, lower evaporative water loss (EWL) and/or higher resting metabolic rate (RMR) in a passerine bird, the white-browed sparrow-weaver (Plocepasser mahali). We used open-system flow-through respirometry to measure EWL, RMR and Tb in sparrow-weavers experiencing Ta = 36-44 °C and chamber humidities of 6, 13, 19 or 25 g m- 3. Increasing humidity was associated with significantly higher Tb. The strongest effect of humidity, however, involved significant increases in RMR; at Ta = 40 °C, RMR at a humidity of 25 g m- 3 was ~ 40% higher compared to a humidity of 6 g m- 3. Moreover, the interaction between Ta and humidity exerted a significant effect on the ratio of evaporative heat loss (EHL) to metabolic heat production (MHP), evident as an increasing effect of humidity with increasing Ta. Our results, when compared with those of the limited number of previous studies that involved similar ranges of Ta and humidity, reveal that the relative effects of humidity on EWL and RMR vary among avian taxa, and support the notion that the overall effect of high humidity is a reduction in maximum EHL/MHP.

Authors+Show Affiliations

South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, Pretoria, South Africa. DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa.South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, Pretoria, South Africa. DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa.South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, Pretoria, South Africa. aemckechnie@zoology.up.ac.za. DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa. aemckechnie@zoology.up.ac.za.

Pub Type(s)

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

Language

eng

PubMed ID

30805750

Citation

van Dyk, Monique, et al. "Interactions Between Humidity and Evaporative Heat Dissipation in a Passerine Bird." Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, vol. 189, no. 2, 2019, pp. 299-308.
van Dyk M, Noakes MJ, McKechnie AE. Interactions between humidity and evaporative heat dissipation in a passerine bird. J Comp Physiol B, Biochem Syst Environ Physiol. 2019;189(2):299-308.
van Dyk, M., Noakes, M. J., & McKechnie, A. E. (2019). Interactions between humidity and evaporative heat dissipation in a passerine bird. Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, 189(2), 299-308. https://doi.org/10.1007/s00360-019-01210-2
van Dyk M, Noakes MJ, McKechnie AE. Interactions Between Humidity and Evaporative Heat Dissipation in a Passerine Bird. J Comp Physiol B, Biochem Syst Environ Physiol. 2019;189(2):299-308. PubMed PMID: 30805750.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Interactions between humidity and evaporative heat dissipation in a passerine bird. AU - van Dyk,Monique, AU - Noakes,Matthew J, AU - McKechnie,Andrew E, Y1 - 2019/02/25/ PY - 2018/12/13/received PY - 2019/02/17/accepted PY - 2019/02/14/revised PY - 2019/2/26/pubmed PY - 2019/2/26/medline PY - 2019/2/27/entrez KW - Body temperature KW - Evaporative water loss KW - Humidity KW - Plocepasser mahali KW - Resting metabolic rate KW - Vapor pressure deficit KW - White-browed sparrow-weaver SP - 299 EP - 308 JF - Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology JO - J. Comp. Physiol. B, Biochem. Syst. Environ. Physiol. VL - 189 IS - 2 N2 - Environmental humidity is thought to be a major determinant of evaporative cooling capacity at high air temperatures (Ta), but the technical challenges of experimentally manipulating humidity in respirometry chambers have resulted in far less being known about the effects of humidity compared to those of Ta. We tested the prediction that at Ta approaching and exceeding normothermic body temperature (Tb), high humidity would result in higher Tb, lower evaporative water loss (EWL) and/or higher resting metabolic rate (RMR) in a passerine bird, the white-browed sparrow-weaver (Plocepasser mahali). We used open-system flow-through respirometry to measure EWL, RMR and Tb in sparrow-weavers experiencing Ta = 36-44 °C and chamber humidities of 6, 13, 19 or 25 g m- 3. Increasing humidity was associated with significantly higher Tb. The strongest effect of humidity, however, involved significant increases in RMR; at Ta = 40 °C, RMR at a humidity of 25 g m- 3 was ~ 40% higher compared to a humidity of 6 g m- 3. Moreover, the interaction between Ta and humidity exerted a significant effect on the ratio of evaporative heat loss (EHL) to metabolic heat production (MHP), evident as an increasing effect of humidity with increasing Ta. Our results, when compared with those of the limited number of previous studies that involved similar ranges of Ta and humidity, reveal that the relative effects of humidity on EWL and RMR vary among avian taxa, and support the notion that the overall effect of high humidity is a reduction in maximum EHL/MHP. SN - 1432-136X UR - https://www.unboundmedicine.com/medline/citation/30805750/Interactions_between_humidity_and_evaporative_heat_dissipation_in_a_passerine_bird_ L2 - http://dx.doi.org/10.1007/s00360-019-01210-2 DB - PRIME DP - Unbound Medicine ER -
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