State of greatly slowed metabolism and low body temperature in winter in certain animals.
True hibernators include many cold-blooded animals and a few mammals (e.g., bats, hedgehogs) that go into a near-dead state with a near-freezing body temperature and very slow breathing and heart rate. Mammals such as bears that sleep in dens with only slightly lowered body temperature wake easily and are not considered true hibernators. Most hibernators build up a reserve of body fat or store food ahead of time. They may wake and eat several times during the winter. Cold-blooded animals must hibernate where the weather drops below freezing. Hibernation's warm-weather equivalent is estivation.