Animal migrations

   In search of food, or a place to breed and rear their young, many animals make long journeys each year. This annual traveling is called migration.
Birds are the best known migrants. Many spend the summer months in cooler lands and fly to warmer places for the winter. Swallows, for instance, arrive in Europe in late spring. They build their nests, rear their young, and feast upon insects. Then, as the fall days grow shorter, they leave in great flocks. Guided only by instinct they fly south to Africa.
   Other animals that migrate include many fishes, whales and seals, some insects, especially butterflies, and the large grazing animals such as deer and antelope.

   Sailors and airmen use a great variety of aids to navigate across the world - compasses, maps, charts, radar, and chronometers for keeping accurate time. But birds have traveled for millions of years without any of these things to guide them.
   After experimenting with starlings and homing pigeons, scientists came to the conclusion that they and many other birds navigate by means of the Sun and the stars. Other experiments suggest that birds can detect the magnetic field of the Earth, just as a compass needle does.