Images of hibernation present bears snuggled into dens, frogs deep in the muck of ponds, woodchucks in burrows, and bats hanging upside down in caves. Cold-blooded animals drop their metabolism, including heartbeat, circulation, and respiration, often for the entire winter. A frog needs so little oxygen during hibernation that it actually breathes through its skin. As the days get longer and warmer, these animals awaken and come up from the depths of the pond or from beneath the leaf litter on the forest floor. Warm-blooded animals head for shelter in caves or underground where they lower their body temperatures.
Some bats roost in cool dry places and some in damp burrows underground.
A performer, Liz Story, tells of keeping a pet bat in her refrigerator when she had to go on tour. While bats are hibernating, their breathing slows down and their heart rate drops from 900 to 20 beats a minute. Hibernating bats need less energy to stay alive. Bats get ready for hibernation by stuffing themselves full of food, especially in the last weeks of warm weather. Their bodies store the extra food as fat.