We know that many animals do not stay in one place . Birds, fish and other animals move from one place to another at a certain time. They move for different reasons: most of them move to find food easily, but others move to get away from places that are too crowed.
When cold weather comes, many birds move to warmer places to find food. Some fish give birth in warm water and move to cold water to feed. The most famous migration(迁移) of the fish, which is called “salmon(大马哈)”. This fish is born in fresh water but it travels many miles to salt water. There it spends its life. When it is old, it returns to its birthplace in fresh water. Then it gives birth and dies there. In northern Europe, there is a kind of mouse. They leave their mountain homes when they become too crowed. They move down to the low land. Sometimes they move all the way to the seaside, and many of them are killed when they fall into the sea.
Recently, scientists have studied the migration of a kind of lobster(龙虾). Every year, when the season of bad weather arrives, the lobsters get into a long line and start to walk across the floor of the ocean. Nobody knows why they do this, and nobody knows where they go.
So, sometimes we know why humans and animals move from one place to another, but at others times we don’t. Maybe living things just like to travel.

Migrations
Some birds	小题1:_______ when cold weather comes
Some fish	Give birth in小题2:______and move to ______ to feed
A kind of mouse	小题3:________ when they become too crowed.
小题4:_________	Walk across the floor of the ocean when the season of 小题5: _______