Solar heat gain in a desert rodent: unexpected increases with wind speed and implications for estimating the heat balance of free-living animals.
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.
Walsberg
G E
GE
Department of Zoology, Arizona State University, Tempe 85287-1501, USA.
Wolf
B O
BO
D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D008954:Models, Biological; D012589:Sciuridae / Q000378:metabolism / Q000502:physiology*; D013472:Sunlight; D014919:Wind