Hibernation is a state of inactivity that some animals enter during cold months to conserve energy. During this time, their body temperature drops, and their heart rate slows down significantly. This allows them to survive on stored body fat when food is scarce. Animals like bears, ground squirrels, and hedgehogs are known to hibernate. They prepare for hibernation by eating extra food in the fall to build up fat reserves. When spring arrives, they wake up and resume their normal activities as temperatures rise and food becomes more available.