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Thermoregulation in resting and active polar bears

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Summary

Polar bears (Ursus maritimus) regulate their body temperatures both physiologically and behaviourally proportional to their level of activity while within the thermoneutral zone. Core temperatures (T c=36.9±0.5°C at rest) varied with the 4th power of walking speed for the two subadult (220 kg) bears tested, whereas subcutaneous temperatures (T sk=35.3±2.2°C at rest) were closely correlated withT c but also varied with wind speed (v a) and ambient temperature (T a). Radiative fur temperatures (T r) were closely correlated withT a and negligibly withT sk. Predictive equations for these temperature relationships were derived by regression analysis. Maximum rates of heat storage (S max) were above that predicted from the literature implying that the polar bear is an energetically costly walker. Radiative heat losses of a resting polar bear amount to between 36–67% of the metabolism and assuming a respiratory heat loss of 7–10%, convective heat losses (by difference) would thus range from 33–64%. When walking, the cooling of the fur surface by forced convection and the ‘pendulum’ effect of the moving legs of the bear lead to estimated convective heat losses on the order of 75% of the heat production while radiative losses are reduced to 13–22%. Increasing wind speeds enhance further this reciprocal effect.

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Author notes

  1. Robin C. Best

    Present address: Department of Aquatic Mammal Biology, Instituto Nacional de Pesquisas da Amazônia, C. P. 478, 69,000, Manaus, Amazonas, Brasil

Authors and Affiliations

  1. Department of Zoology, University of Guelph, Guelph, Ontario, Canada

    Robin C. Best

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  1. Robin C. Best
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Best, R.C. Thermoregulation in resting and active polar bears. J Comp Physiol B 146, 63–73 (1982). https://doi.org/10.1007/BF00688718

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  • DOI: https://doi.org/10.1007/BF00688718

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