Hibernation

Periodically, perhaps every two weeks or so, the hibernating animal will arouse and take a few deep breaths to refresh its air supply, or in the case of the chipmunk, to grab a bite to eat. If it is a particularly mild winter day, some animals may venture above ground. These animals, including chipmunks, skunks, and raccoons, are sometimes called "shallow" hibernators.

Arousal begins with an increase in the heart rate. Blood vessels dilate, particularly around the heart, lungs, and brain, leading to an increased breathing rate. Blood also flows into the layer of brown fat, increasing activity there and causing a rise in body temperature. Eventually, the increase in circulation and metabolic activity spreads throughout the body, reaching the hindquarters last. It usually takes several hours for the animal to become fully active.