Migration
Animals do many different, amazing things to get through the winter. Some of them “migrate”. This means they travel to other places where the weather is warmer or they can find food.
Many birds migrate in the fall. Because the trip can be dangerous, some travel in large flocks. For example, wild geese fly in noisy, “V”-shaped groups. Other kinds of birds fly alone.
How do they know when it is time to leave for the winter? Scientists are still studying this. Many see migration as part of a yearly cycle of changes a bird goes through. The cycle is controlled by changes in the amount of daylight and the weather.
Birds can fly very long distances. For example, the Arctic tern(北极燕鸥) nests close to the North Pole in summer. In autumn, it flies south all the way to Antarctica(南极洲). Each spring it returns north again.
Most birds migrate shorter distances. But how do they find their way to the same place each year? Birds seem to navigate like sailors once did, using the sun, moon and stars for direction. They also seem to have a compass in their brain for using the Earth’s magnetic field.
