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Some animals enter a state of hibernation as the winter approaches, spending the cold months in a deep sleep. By doing so, they avoid having to cope with the scarcity of food and harsh weather conditions. Before entering hibernation, animals prepare by eating large amounts of food. In Animal Physiology: A Winter Sleep, the vital signs of a transmitter-equipped Canadian ground squirrel are tracked, while cameras record the movements in its nest. Heart and metabolic rates drop, and periods of awakening occur so that the animal can eliminate wastes.