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migratory birds
Migratory birds are some of nature’s most magnificent creatures, playing significant ecological, economic, and cultural roles internationally. Migration is predicated primarily upon food resources. Since most insects become unavailable during our harsh winters, insect-eating birds find abundant food resources in the tropics. Many raptor species also follow this migrating food chain.Bird migration is the regular seasonal movement, often north and south along a flyway between breeding and wintering grounds, undertaken by many species of birds. Migration, which carries high costs in predation and mortality, including from hunting by humans, is driven primarily by availability of food. Migration occurs mainly in the Northern Hemisphere where birds are funnelled on to specific routes by natural barriers such as the Mediterranean Sea.The timing of migration is controlled primarily by changes in day length. Migrating birds navigate using celestial cues from the sun and stars, the earth's magnetic field, and probably also mental maps. Migration has developed independently in different groups of birds and does not appear to require genetic change; some birds have acquired migratory behaviour since the last ice age.


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