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Adaptive thermoregulation during summer in two populations of an arid-zone passerine.
Ecology 2013; 94(5):1142-54E

Abstract

Heterothermy plays an important role in lowering the costs of thermoregulation in endotherms by reducing water and energy requirements. We tested predictions that birds in arid habitats should express fine-scale variation in their thermoregulatory patterns as a function of prevailing climatic conditions. We assessed effects of air temperature (Tair) and water vapor pressure deficit (D) on body temperature (Tb) in free-living White-browed Sparrow-Weavers (Plocepasser mahali) during summer in two arid habitats in the Kalahari Desert, South Africa, using data from a dry period at a hot, desert site (n=7 birds), and during a dry period (n=4 birds) and a wet period (n=5 birds) at a milder, semi-desert site. The desert birds maintained a significantly higher set-point Tb (41.5 degrees+/-0.2 degrees C, mean-SD) than semi-desert birds (40.2 degrees+/-0.2 degrees C). During the warmest part of day (12:00-18:00 hours), Tb increased significantly during periods of high Tair and/or high humidity, and mean and maximum Tb were up to 1.40 and 2.3 degrees C, respectively, above normal levels. However, as Tair increased, birds at the desert site maintained Tb at or below set-point levels for a greater proportion of the time than birds at the semi-desert site. Birds at the desert site also expressed a greater magnitude of daily heterothermy (heterothermy index, HI=2.4 degrees+/-0.3 degrees C, mean+/-SD) than birds at the semi-desert site: the latter population showed a greater magnitude of heterothermy during a dry period (HI=2.1 degrees+/-0.3 degrees C) than during a wet period (HI=1.6 degrees+/-0.2 degrees C). Birds continued foraging throughout the warmest part of the day, despite the fact that heat dissipation (percentage of time spent panting and wing-spreading) increased significantly with increasing Tair. Our findings reveal that populations can vary in their thermoregulatory responses in both space and time and suggest that small changes in Tair can have significant effects on thermoregulation in free-ranging desert birds, even when Tair<Tb. These data have important implications for assessing vulnerability of species to climate change, suggesting that sensitivity should be assessed at the population, rather than species, level.

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. smitbe@gmail.comNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

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

Language

eng

PubMed ID

23858654

Citation

Smit, B, et al. "Adaptive Thermoregulation During Summer in Two Populations of an Arid-zone Passerine." Ecology, vol. 94, no. 5, 2013, pp. 1142-54.
Smit B, Harding CT, Hockey PA, et al. Adaptive thermoregulation during summer in two populations of an arid-zone passerine. Ecology. 2013;94(5):1142-54.
Smit, B., Harding, C. T., Hockey, P. A., & McKechnie, A. E. (2013). Adaptive thermoregulation during summer in two populations of an arid-zone passerine. Ecology, 94(5), pp. 1142-54.
Smit B, et al. Adaptive Thermoregulation During Summer in Two Populations of an Arid-zone Passerine. Ecology. 2013;94(5):1142-54. PubMed PMID: 23858654.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Adaptive thermoregulation during summer in two populations of an arid-zone passerine. AU - Smit,B, AU - Harding,C T, AU - Hockey,P A R, AU - McKechnie,A E, PY - 2013/7/18/entrez PY - 2013/7/19/pubmed PY - 2013/8/16/medline SP - 1142 EP - 54 JF - Ecology JO - Ecology VL - 94 IS - 5 N2 - Heterothermy plays an important role in lowering the costs of thermoregulation in endotherms by reducing water and energy requirements. We tested predictions that birds in arid habitats should express fine-scale variation in their thermoregulatory patterns as a function of prevailing climatic conditions. We assessed effects of air temperature (Tair) and water vapor pressure deficit (D) on body temperature (Tb) in free-living White-browed Sparrow-Weavers (Plocepasser mahali) during summer in two arid habitats in the Kalahari Desert, South Africa, using data from a dry period at a hot, desert site (n=7 birds), and during a dry period (n=4 birds) and a wet period (n=5 birds) at a milder, semi-desert site. The desert birds maintained a significantly higher set-point Tb (41.5 degrees+/-0.2 degrees C, mean-SD) than semi-desert birds (40.2 degrees+/-0.2 degrees C). During the warmest part of day (12:00-18:00 hours), Tb increased significantly during periods of high Tair and/or high humidity, and mean and maximum Tb were up to 1.40 and 2.3 degrees C, respectively, above normal levels. However, as Tair increased, birds at the desert site maintained Tb at or below set-point levels for a greater proportion of the time than birds at the semi-desert site. Birds at the desert site also expressed a greater magnitude of daily heterothermy (heterothermy index, HI=2.4 degrees+/-0.3 degrees C, mean+/-SD) than birds at the semi-desert site: the latter population showed a greater magnitude of heterothermy during a dry period (HI=2.1 degrees+/-0.3 degrees C) than during a wet period (HI=1.6 degrees+/-0.2 degrees C). Birds continued foraging throughout the warmest part of the day, despite the fact that heat dissipation (percentage of time spent panting and wing-spreading) increased significantly with increasing Tair. Our findings reveal that populations can vary in their thermoregulatory responses in both space and time and suggest that small changes in Tair can have significant effects on thermoregulation in free-ranging desert birds, even when Tair<Tb. These data have important implications for assessing vulnerability of species to climate change, suggesting that sensitivity should be assessed at the population, rather than species, level. SN - 0012-9658 UR - https://www.unboundmedicine.com/medline/citation/23858654/Adaptive_thermoregulation_during_summer_in_two_populations_of_an_arid_zone_passerine_ DB - PRIME DP - Unbound Medicine ER -