Migration is the mass movement of groups of animals or birds. It is caused by the need to find food, by climatic changes during the year, and by the need to breed. Every autumn, for example, swallows gather in large flocks to rest before they begin their long migration to Africa. Swallows, and their relatives, swifts and martins, all migrate to Africa when the weather becomes too cold for them to catch their insect prey. They return in the spring when the weather in northern Europe begins to warm up. The Arctic tern makes the longest-known migration of any bird we know, by travelling from the Arctic to the Antarctic and then back again. On its flight it passes through Japan, Alaska, Canada and Fiji before returning home again to breed.
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Fact File: Many fish migrate in both fresh water and the ocean. Tuna make some of the longest migrations. The need to migrate is due to sea temperature, as fish need the correct temperature in order to breed. |
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