Migration and Hibernation

Winter is a hard time

Imagine you are a small animal living in a wood. In summer there are insects to eat, fruit on the bushes and warm days. But when winter comes, everything changes. The days get short and cold, the leaves fall, the insects disappear and the ground may freeze. Suddenly it is very hard to find food and very hard to stay warm.

So what can an animal do? Animals cannot put on a big coat or turn up the heating like we can. Instead, over millions of years, different animals have found clever ways to survive the cold. Two of the most amazing answers are migration and hibernation. Let's find out how each one works, and why.

Migration: a long journey to a better place

Migration means travelling a long way to find better weather and more food, and then travelling back again when things improve. Animals that migrate do not stay and fight the winter — they simply leave it behind.

The most famous migrators are birds. Every autumn, swallows leave Europe and fly all the way to Africa — a journey of thousands of miles! They do this because they eat flying insects, and in a cold European winter there are almost no insects to catch. In Africa it is warm and full of food. When spring returns to Europe, the swallows fly all the way back to build their nests.

Birds are not the only migrators:

• Whales swim huge distances to find food and to have their babies in warm seas.
• Wildebeest in Africa walk in enormous herds, following the rain to fresh grass.
• Monarch butterflies in America travel south for the winter — and they are so light that the wind helps carry them!
• Salmon are special: they migrate from the sea up rivers to lay their eggs.

The big question is: how do animals know where to go? Scientists think they use the sun, the stars, and even an invisible force called the Earth's magnetic field, like a built-in compass. Many young birds make the journey for the very first time without any grown-up to show them the way. That is one of nature's great mysteries.

You can read more about why food matters so much in food chains and ecosystems.

Hibernation: a deep winter sleep

The other clever answer is to stay put and hibernate. Hibernation is a very deep, special sleep that lasts through the coldest part of the year.

When an animal hibernates, its body does something amazing. It slows right down:

• The heartbeat becomes very, very slow — a hedgehog's heart can drop from 190 beats a minute to just 20.
• The breathing slows down too.
• The body temperature falls until the animal feels cold to touch.

Why does the body do this? Because a slow, cold body burns hardly any energy. The animal does not need to find food every day — it can survive for weeks or months on the fat it stored up in autumn. That is why hedgehogs, dormice and bears eat so much in late summer: they are filling up their fuel tanks before the long sleep.

Animals that hibernate include hedgehogs, dormice, bats, frogs and tortoises. (Bears go into a lighter winter sleep and can wake up more easily, so some scientists call theirs a slightly different kind of rest.)

Hibernating animals choose a safe, hidden, sheltered spot — under a pile of leaves, in a hollow log, or deep in a burrow — so that nothing disturbs them and the cold cannot reach them too easily.

A third way: stay and adapt

Not every animal migrates or hibernates. Many simply stay active and adapt. A fox grows a thicker, warmer coat of fur. A squirrel buries hundreds of nuts in autumn, then digs them up all winter. A rabbit stays in its cosy burrow on the coldest days. These animals have found ways to keep going right through the snow.

Why it matters

Migration and hibernation show us how clever and tough nature really is. Every animal has its own way of solving the same big problem — surviving the cold. If you ever notice the swallows disappearing in autumn, or find a hedgehog curled up asleep, you are watching one of these brilliant survival tricks in action. Learning about animal homes and shelters, such as in animals and their homes, helps us understand where these creatures go when winter comes.

Activity: be a winter detective

Try this when the weather turns cold:

1. Watch the sky. In autumn, look up. Can you spot birds flying together in a group or a V-shape? They may be getting ready to migrate.
2. Make a hibernation home. With a grown-up, gather a small pile of dry leaves and twigs in a quiet corner of a garden. A hedgehog might just choose it for a winter sleep — but do not disturb it once winter starts!
3. Keep a chart. Write down which animals you still see in winter (like robins and squirrels) and which ones have vanished (like swallows and butterflies). Can you guess which ones migrated and which are hibernating?

You will be amazed how much nature is busy doing, even on the coldest, quietest days.