Bear Hibernation
One of the most remarkable things that bears do is also one of the biggest cliches in most people's knowledge of them. A great deal of scientific research in recent years has gone into the study of how bears hibernate. There are potential applications of great importance in this, including space travel. If you read in a bear book that bears don't undergo "true" hibernation, you should know that the information is out of date. A 400-pound bear simply does't hibernate the same way as a 1-pound squirrel does, but it is just as efficient, maybe more so. The basic purpose of hibernation appears to be to reduce the number of calories burned when food is scarce or unavailable. It should be thought of as a response to seasonal food shortages rather than cold temperatures. The exact triggers that induce hibernation are still not well known.
The hibernation that small mammals do consists of deep comatose sleep, body temperature only a few degrees above freezing, and heart and breathing rate slowed to almost undetectable levels. Such an extremely low rate of metabolism, however, is unable to indefinitely sustain life. The animal must wake up every few days as metabolic poisons accumulate, go out to urinate and defecate, eat and drink something, then drift back down to sleep again. The frequent need to wake up reduces the efficiency of the hibernation so that fewer calories are saved than you might think. This pattern is forced on small animals as they rapidly lose heat due to their small size. They cannot hibernate with meaningful efficiency unless their body temperature is very low.
Bears do it differently: Their body temperature only falls about a maximum of 10 degrees. The heart rate falls to about 1/5 the active, non-hibernating rate, and the breathing rate slows similarly. Although asleep, they are easily aroused and can get up and be active quickly if necessary. What makes this hibernation is that an undisturbed bear stays asleep all winter long, sometimes without even changing position once they are settled in. The bear does not eat or drink, urinate or defecate the entire time. In severe northern climates, hibernation may last 7 months or longer, and the bear can maintain this deceptively shallow appearing state continuously the whole time. The bear sustains his life force during all that time purely on the air he breathes and by burning his body fat. The great bulk of the bear allows him to sustain body temperatures close to normal so he can maintain necessary life processes. Despite the often intense cold around him, he only burns about half as many calories as he does in the warm months when he is awake.
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