Why do some birds fly away in winter?

TankiRanki, in autumn some birds just disappear. Where do they all go?

RankiThey set off on long journeys, some of them across whole oceans. And the numbers are huge. I love this one.

Winter means less food

Many birds eat insects, worms, seeds or fruit. In summer there is plenty of all of it. But in winter, most insects hide away, the ground can freeze and plants stop growing. Food becomes hard to find.

Some birds solve this problem by flying away. They travel to warmer places where there is still plenty to eat. In spring they come back to build nests and raise their chicks. This journey, there and back every year, is called migration.

Not all birds leave, though. Many robins, blackbirds and sparrows stay all year. They find seeds and berries, and they fluff up their feathers to keep warm.

Amazing journeys

Swallows that nest in Britain spend the winter in southern Africa. That is a trip of thousands of kilometres. On the way, they fly over mountains, seas and the huge Sahara desert.

The record holder is the Arctic tern, a small white seabird. It spends the summer in the far north of the world. Then it flies all the way to the icy seas around Antarctica, and back again. Antarctica is the frozen land at the very bottom of the Earth.

Scientists fixed tiny trackers to some Arctic terns. They found that the birds fly about 70,000 kilometres every year. That is like flying almost twice around the whole Earth.

TankiSeventy thousand kilometres? My legs feel tired just thinking about it.

RankiGood thing terns use wings, not legs. And they get two summers every year!

How do birds find their way?

Birds have no maps. Still, many of them find the same place year after year, sometimes even the same barn. Scientists think birds use several clues together.

• The Sun shows them the direction during the day.
• The stars guide birds that fly at night.
• The Earth’s magnetic field gives them an invisible sense of north and south.
• Landmarks they remember, such as rivers, coastlines and mountains, show them the way.

The magnetic field is the most mysterious clue. It is an invisible force all around the Earth. It makes the needle of a compass point north. Birds seem to feel it, as if they had a compass inside them. Scientists are still finding out exactly how this works.

Why geese fly in a V

Big birds like geese often fly in a V shape. Each flapping wing stirs up the air behind it. A bird just behind and to the side can ride on this rising air. That saves energy, so the whole flock can fly further.

The bird at the front has the hardest job. Scientists have seen that birds flying in a V often take turns at the front. It is good teamwork, high up in the sky.

TankiSo birds leave to find food, not just to escape the cold. And they find their way with the Sun, the stars and a magnetic sense.

RankiThat is it. Keep an eye on the sky in spring, and you can welcome them home.