Certain mammals have what many people might consider the good fortune to be able to sleep through the winter—to hibernate. They bed down in the fall and, for all intents and purposes, don't arise again until the spring. Raccoons and skunks do it. So do woodchucks and chipmunks, hamsters and hedgehogs, bats and bears. Some, particularly rodents, sleep very deeply, while others, such as bears, slumber more lightly.
One of the most celebrated hibernators is the American black bear (Ursus americanus). It can go for as long as 100 days without eating, drinking, urinating, defecating, or exercising. Preparations for over-wintering begin in the summer, when bears begin gorging carbohydrate-rich berries and other foods to put on weight. During this period, they can gain as much as 30 pounds per week. In early autumn, a bear (and its cubs, if any) will rake leaves, twigs, and other plant materials into the den to form a nest. Throughout the fall its activity level steadily drops until it ends completely when the bear enters its den.
Bears make dens in burrows, caves, hollowed-out trees, and rock crevices. Dens of the bears Rogers studies in Minnesota typically feature entrances just large enough for a bear to squeeze through; interior chambers measure two-and-a-half to five feet wide and two to three feet high.
It's cramped for a single bear, much less for a mother and her cubs. But that's the way bears like it: Black bears do no exercising of any sort during the winter months, preferring to lie rolled into a tight ball, with their heads between their forepaws and their heavily furred backs exposed to the worst of the cold. Dens themselves offer little insulation. In Minnesota, dens with open entrances are about as warm inside as outside, where the temperature, Rogers says, often plummets to as low as -28°F. Bears keep warm using their great bulk, their inches-deep layer of fat, and their fur, which more than doubles its insulative value during the fall. Why is it important that the American black bear over eat
carbohydrate rich foods before hibernating in the winter?
How do bears utilize their fat stores during the winter?
Can you find an example of homeostasis in this article? Explain.
http://www.pbs.org/wgbh/nova/satoyama/hibernation.html
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