请用英语100-200字介绍一下松鼠的冬眠~~

Animals that hibernate include bats, some species of ground squirrels and other rodents, mouse lemurs, the West European Hedgehog and other insectivores, monotremes and marsupials. Even some rattlesnakes, such as the Western Diamondback, are known to hibernate in caves every winter. Historically, Pliny the Elder believed that swallows hibernated, and ornithologist Gilbert White pointed to anecdotal evidence in The Natural History of Selborne that indicated as much. Birds typically do not hibernate, instead utilizing torpor. However the Common Poorwill does hibernate. Many experts believe that the processes of daily torpor and hibernation form a continuum.

One animal that some famously consider a hibernator is the bear, although bears do not go into "true hibernation". During a bear's winter sleep state, the degree of metabolic depression is much less than that observed in smaller mammals. Many prefer to use the term "denning". The bear's body t