I heard one story about a bear that denned by lying on the ground and letting the snow cover it and another seen denning up in an eagle’s nest. Their den may be completely underground, partially exposed until covered with snow, or out in the open. They might also choose a hollow tree or a small dense stand of conifers. When I am trying to find a likely bear den location, I look for an overturned tree with a large root wad bears love to dig in beneath the roots. A sow that had cubs last winter may allow the yearlings to den with her for their first winter, but a pregnant sow will choose a site where she can protect and tend her cubs when they are born. Bears select a den just large enough to fit them an adult male will fit into a hole that might be only four feet in diameter. Most people think of a cave as a standard bear den, but in fact a black bear can choose any number of different options. However, as researchers discovered that bears can lower their heart rate down to eight beats per minute, and breathe once every 45 seconds, they have decided hibernation is still an accurate description of their dormant or semi-dormant overwinter condition. Torpor allows bears to rouse more easily than if they were in true hibernation, so they reposition, groom themselves, give birth, and if necessary, escape danger readily. Bears do not enter true hibernation, but more of a deep winter sleep, or torpor. True hibernation by mammals, like chipmunks and groundhogs, includes lowering body temperature to near freezing. They drop into a deep sleep, which slows their metabolism and allows them to live off their body fat stored through the summer and fall months. Black bears enter their dens in late November or early December.
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