根据短文内容完成表格，每空一词。

Every year some birds fly south when days turn cold and leaves from trees start to fall. They travel a very long way to find a warmer winter. This travel is called migration （迁徙）.

Birds do that because in winter most of the plants die and some insects (昆虫）hide. They fly away to find enough food. The next year when there is plenty of food for them to eat they will come back.

Birds fly in some ways. For example, they fly in groups like the letter V or in a row. The trip is often hard and it may be dangerous. But they never get lost because they look at the sun, the moon and stars.

The Migration of ____1____
When they fly south	Days turn cold and ____2____ from trees start to fall.
What the purpose is	They fly away in ____3____ to find enough food.
____4____ the trip is	It is often hard and dangerous.
____5____ they never get lost	Because they look at the sun, the moon and stars.