Some mammals survive periods of cold and limited food by entering hibernation. Their bod reduce nor activity a consume sto energy mo slowly a breathing bec less freq and inte temperatures fa below ordinary levels. This state differs from an ordinary night of sleep. Preparing for it may involve accumulating substantial fat reserves before winter begins. The timing and depth of hibernation vary among species, and animals may periodically become active again. By reducing their energy needs during a difficult season, these mammals can remain in habitats that provide too little food to support their usual level of activity.

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