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Snow geeseSnow geese Animals are always on the move in search of fresh sources of food. Some travel at the same time each year to places where the new season brings a more favourable climate for feeding or breeding. Called migration, these journeys are sometimes made to distant parts of the world. Birds are the main group of migrating animals because their power of flight allows them to cover long distances rapidly. Some land mammals migrate too, such as caribou. In Australia, herds of kangaroos and flocks of emus travel hundreds of kilometres across deserts in search of areas where rain has brought fresh plant growth.

Snow geese flock in North DakotaSnow geese flock in North Dakota
Migration routes that are mainly over landMigration routes that are mainly over land

Regular journeys

For most migrating creatures the journeys are at a regular time each year and usually follow the same routes as well. In the polar lands of the far north, the summer is short but the long hours of daylight and warmth allow plenty of plant growth. There are few resident animals to eat the plants. So birds such as geese fly up from the south in the spring to feed and raise their young in the Arctic. Then in the autumn, before the long, dark, icy winter grips the polar regions, they return south to temperate Europe, Asia and North America.

Ocean migration routesOcean migration routesAnother group of migrating birds, such as swallows and swifts, spend spring and summer in Northern temperate lands, feeding and breeding. Then, in autumn, they fly south to the warmth of the tropics.

Many animal migrants that go by air—birds, bats and insects—prefer to avoid travelling over the sea. They may be unable to find their usual sources of food, or to rest from long periods of flight. If they do need to cross the sea on their journey, they will cross where there are narrow straits or island "stepping-stones".

A willow warbler’s body holds enough food to give it the energy it needs to fly 60 hours non-stop. This enables it to fly across deserts and seas on its migratory route.

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