5-3 Bird Migration

Bird Migration

  Many birds make seasonal migrations.  How far they travel depends on the type of food they eat.  Seed-eating birds just need to avoid the worst of the weather.  Seeds can be found in the winter.  Seed-eating birds may migrate just a short distance.  Insect-eating birds may have to travel south because there may be nothing to eat in the far north in the winter.  They need to fly hundreds or thousands of kilometers south to ensure a supply of insect food.  They return north for the summer when there will be plenty of insects.  

  Some of the distances covered by birds on migration are huge.  Willow warblers can travel 12,000 km (7,500 mi.) twice a year.  The longest migration route is made by the arctic tern, which travels from the Arctic to the Antarctic and back.  Many other seabirds also make long trips across the oceans.  Most migrating land birds avoid sea crossings as much as possible.  This is why great congregations of migratory birds can be seen crossing narrow straits such as between Gibraltar and Africa.  A small bird like a warbler can put on enough fat to double its weight before migration.  It may then have enough fuel to fly for up to three days without rest.