We know that many animals do not stay in one place.
我们知道，许多动物并不会待在一个地方。
Birds, fish and other animals move from one place to another at a certain time.
鸟类、鱼类和其他动物会在某个特定的时间从一个地方移动到另一个地方。
They move for different reasons; most of them move to find food more easily, but others move to get away from places that are too crowded.
它们迁徙的原因各不相同；大多数是为了更容易地寻找食物，但也有一些是为了远离过于拥挤的地方。
When cold weather comes, many birds move to warmer places to find food.
当寒冷的天气到来时，许多鸟类会迁徙到更温暖的地方寻找食物。
Some fishes give birth in warm water and move to cold water to feed.
一些鱼类在温水中产卵，然后移动到冷水中觅食。
The most famous migration is probably the migration of fish, which is called "salmon".
最著名的迁徙或许就是这种被称为“鲑鱼”的鱼类的迁徙。
This fish is born in fresh water but it travels many miles to salt water.
这种鱼出生在淡水中，但它会游行很多英里到达咸水区。
There it spends its life.
它在那里度过一生。
When it is old, it returns to its birthplace in fresh water.
当它老了的时候，它会回到淡水中的出生地。
Then it gives birth and dies.
然后它产下后代并死去。
In northern Europe, there is a kind of mouse.
在北欧，有一种老鼠。
They leave their mountain homes when they become too crowded.
当居住地变得过于拥挤时，它们会离开山里的家。
They move down to the low land.
它们向下移动到低地。
Sometimes they move all the way to the seaside, and many of them are killed when they fall into the sea.
有时它们一直走到海边，其中许多在掉进大海时丧命。
Full Text in English
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 more easily, but others move to get away from places that are too crowded. When cold weather comes, many birds move to warmer places to find food. Some fishes give birth in warm water and move to cold water to feed. The most famous migration is probably the migration of fish, which is called "salmon". 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. In northern Europe, there is a kind of mouse. They leave their mountain homes when they become too crowded. 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.