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| Serengeti migration |
Wild animals can travel great distances when they migrate to their breeding grounds. A special study has been made on the migration of birds. Rings are placed on their legs, which carry a number and an address. When a ringed bird is caught it is possible to tell how far it has come from its original home. One of the longest journeys is made each year by the Arctic tern. It breeds in the north, and travels to and fro across the world to winter in the south, a round journey of some 32,000 kilometres (20,000 miles). Even tiny hummingbirds can fly over the sea, from Florida in the United States to the island of Cuba, some 800 kilometres (500 miles) away. Passenger or racing pigeons can find their way back to their lofts when released far away from them. They have been used for carrying messages. Even some butterflies and moths migrate. Each summer a number come to northern Europe from north Africa.
Young salmon go down to the sea to grow up, then return to spawn in the rivers in which they were born. Eels start their lives in the Sargasso Sea in the mid-Atlantic Ocean. The tiny larva of the eels are then carried by sea currents to the shores of Europe on a 3,200-kilometre (2,000-mile) journey which takes nearly three years. Every spring, giant whales travel south to the Antarctic to feed on the plankton, then go north again to have their calves. Herds of antelopes go on migrations across the African plains, and reindeer move south as the Arctic winter closes in.
There is still a great deal of mystery attached to these animal journeys and little is yet known about the way in which so many different creatures find their way across the world.
