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Grand Teton National Park Report

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Temperature data sensors were placed in the abdominal cavity, on the neck and outside the den of 5 black bears (Ursus americanus) during early winter and removed at the end of winter prior to the bear's leaving their den. Abdominal temperature remained around 35°-36°C and did not appear to exhibit circadian rhythmicity. Neck surface temperature of bears, however, demonstrated elevated spikes from 2° to 30°C about 4 times each day. We suggest that bears engage in bouts of muscular activity during the winter denning period to retain muscle strength and may vasodilate the skin to dissipate the heat rather than elevate their core body temperature and arouse from torpor.