Hibernation

Hibernation is a [blank] for many creatures - from butterflies to bats - to survive cold, dark winters without having to forage for food or migrate to somewhere warmer. [blank] , they turn down their metabolisms to save energy. Animals in hot climates also undergo a form of hibernation called estivation. This works in a similar way and enables them to survive extreme heat, drought, or lack of food.Hibernating is much more [blank] than simply sleeping, though. Depending on the species, it can vary from long, deep unconsciousness to light spells of inactivity. But hibernation carries risks, as the dormant animal is [blank] to predators and the unpredictable climate.