What are hibernation and migration?

In winter, many places become cold, and food is hard to find. Animals have different solutions.

Hibernation is a long, deep sleep. During it, the animal's body temperature drops, its heartbeat and breathing slow right down, and it uses very little energy. Before winter, the animal eats a lot and builds up a layer of fat to live on. Hedgehogs, dormice, bats and some squirrels hibernate. Bears sleep deeply for much of winter too, but they wake more easily. Some animals also sleep through very hot, dry spells, which is called estivation.

Migration is a regular trip, often twice a year, to a place with more food or better weather. Many birds do it. Swallows breed in Europe in summer and spend winter in Africa, flying thousands of kilometres. The Arctic tern travels from the Arctic to the Antarctic and back every year, covering roughly 70,000 kilometres, one of the longest migrations of any animal. Monarch butterflies fly from Canada and the United States to forests in Mexico. In East Africa, millions of wildebeest and zebras follow the rains across the Serengeti. Humpback whales swim from cold feeding waters to warm seas to have their calves. Salmon swim back up rivers to breed.

How do migrating animals find their way? Different species use the Sun, the stars, Earth's magnetic field, smells and landmarks. Many young birds are born with an inbuilt sense of direction.

Both are examples of adaptations: behaviour that helps animals cope with the changing seasons. Other animals just stay and cope, like deer that grow thicker coats, or squirrels that store nuts. Where an animal lives (see habitats) decides which strategy suits it.

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