Solar heat gain in a desert rodent: unexpected increases with wind speed and implications for estimating the heat balance of free-living animals

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Biochemical, systemic, and environmental physiology, 1995-09, Vol.165 (4), p.306-314
• Main Authors: Walsberg, G E, Wolf, B O
• Format: Article
• Language: English
• Subjects: Animals; Body Temperature Regulation - physiology; Models, Biological; Sciuridae - metabolism; Sciuridae - physiology; Sunlight; Wind
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/BF00367314

We quantified metabolic power consumption as a function of wind speed in the presence and absence of simulated solar radiation in rock squirrels, Spermophilus variegatus, a diurnal rodent inhabiting arid regions of Mexico and the western United States. In the absence of solar radiation, metabolic rate increased 2.2-fold as wind speed increased from 0.25 to 4.0m.s-1. Whole-body thermal resistance declined 56% as wind speed increased over this range, indicating that body insulation in this species is much more sensitive to wind disruption than in other mammals. In the presence of 950W.m-2 simulated solar radiation, metabolic rate increased 2.3-fold as wind speed was elevated from 0.25 to 4.0m.s-1. Solar heat gain, calculated as the reduction in metabolic heat production associated with the addition of solar radiation, increased with wind speed from 1.26mW.g-1 at 0.25m.s-1 to 2.92mW.g-1 at 4.0m.s-1. This increase is opposite to theoretical expectations. Both the unexpected increase in solar heat gain at elevated wind speeds and the large-scale reduction of coat insulation suggests that assumptions often used in heat-transfer analyses of animals can produce important errors.