Why Animals Hibernate

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Hibernation is a deep, energy-saving sleep that some animals fall into to survive winter, when the weather turns cold and food becomes hard to find. It is very different from a normal night's sleep: the animal's body switches to a kind of 'low power mode' — its heartbeat slows right down, its breathing becomes shallow, and its body temperature drops so it burns as little energy as possible.

Animals prepare for hibernation in autumn by eating a lot of food to build up a store of body fat. Because they cannot hunt or forage through winter, that stored fat becomes the fuel their slowed-down body slowly burns over the cold months. When spring returns and the air warms up, the animal's heartbeat speeds up, its body warms, and it wakes — usually very hungry.

Key ideas young learners will grasp include why winter is the hard season, how slowing the body saves energy, which animals actually hibernate (such as bears, hedgehogs, frogs and bats), and why fat is stored as winter fuel.

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Frequently asked questions

Why do animals hibernate?
Animals hibernate to survive winter, when it is very cold and food such as plants, insects and small prey becomes scarce. By going into a deep sleep, they use far less energy and can live off stored body fat until food returns in spring.
Is hibernation the same as normal sleep?
No. In normal sleep the body still works fairly normally, but during hibernation the animal's body drops into a 'low power mode' — the heartbeat slows dramatically, breathing becomes shallow, and body temperature falls to save as much energy as possible.
Which animals actually hibernate?
Animals that hibernate or enter a similar deep winter dormancy include bears, hedgehogs, frogs and bats. Animals like lions, elephants and dogs do not hibernate.
How do animals survive without eating all winter?
In autumn they eat a lot of food to build up a thick layer of body fat. Their slowed-down body slowly burns this stored fat as fuel throughout winter, so they do not need to find food while hibernating.
When do hibernating animals wake up?
They wake in spring, when the air warms up and food becomes available again. Their heartbeat speeds up, their body temperature rises, and they slowly become active — usually very hungry after the long sleep.

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