Hibernation is a physiological state in which metabolism, body functions, and body temperature decrease. These allow survival over extended periods of cold temperature and reduced food supply. Many warm-blooded mammals, particularly in temperate and arctic regions, pass the winter in a state of hibernation. For example, the ground squirrel devours large amounts of food for a month, retreats underground at the right season, has its temperature drop within a few hours, and enters a state of dormancy. The metabolic rate declines about 10% below normal, and the heart rate drops from about 200 beats per minute to about ten. In addition, breathing rate lowers from about 100 times per minute to four. The animal emerges from hibernation quickly, when its metabolism rises and warms the body to a functional level. Some mammals, such as brown bears, enter hibernation in winter but may wake up on a warm day and eat. Bears...