Abstract
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 4.0 m·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 950 W·m-2 simulated solar radiation, metabolic rate increased 2.3-fold as wind speed was elevated from 0.25 to 4.0 m·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 1.26 mW·g-1 at 0.25 m·s-1 to 2.92 mW·g-1 at 4.0 m·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.
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Abbreviations
- α:
-
absorptivity of coat to solar radiation
- ν:
-
kinematic viscosity of air (mm2·s-1)
- ρ:
-
reflectivity of coat to solar radiation
- a r B :
-
expected at zero wind speed (s·m-1)
- A P :
-
projected surface area of animal on plane perpendicular to solar beam (cm2)
- A SKIN :
-
skin surface area (cm2)
- b :
-
Coefficient describing change in r B with change in square-root of wind speed (s1.5·m1.5)
- d :
-
hair diameter (m)
- d:
-
characteristic dimension of animal (m)
- D H :
-
thermal diffusivity of air (m2·s-1)
- E :
-
evaporative heat loss (W·m-2)
- I :
-
probability per unit coat depth that photon will strike hair
- k :
-
constant equalling 1200 J·m-3·°C-1
- l C :
-
coat depth m)
- l H :
-
hair length (m)
- M :
-
metabolic rate (W·m-2)
- n :
-
density of hairs of skin (m-2)
- Q A :
-
solar heat gain to animal (W·m-2)
- Q I :
-
solar irradiance intercepted by animal (W·m-2)
- RQ :
-
respiratory quotient
- r A :
-
thermal resistance of boundary layer (s·m-1)
- r B :
-
whole-body thermal resistance (s·m-1)
- r E :
-
thermal resistance between animal surface and environment s·m-1)
- r R :
-
radiative resistance (s·m-1)
- r S :
-
sum of r B and r E at 0.25 m·s-1 (s·m-1)
- r T :
-
tissue thermal resistance s·m-1)
- T AIR :
-
air temperature (°C)
- T B :
-
body temperature (°C)
- T E :
-
operative temperature of environment (°C)
- T ES :
-
standard operative temperature of environment (°C)
- u :
-
wind speed (m·s-1)
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Communicated by L.C.-H. Wang
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Walsberg, G.E., Wolf, B.O. Solar heat gain in a desert rodent: unexpected increases with wind speed and implications for estimating the heat balance of free-living animals. J Comp Physiol B 165, 306–314 (1995). https://doi.org/10.1007/BF00367314
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DOI: https://doi.org/10.1007/BF00367314