When cold weather comes, many birds move to the south. Many animals do not remain in one place. Moving is a normal part of their lives. Some move to find food more easily, but others move to get away from crowded places or to survive disasters like an earthquake. We can compare this action to people moving for better opportunities.
寒冷天气来临时，许多鸟类会向南方迁徙。许多动物不会固定停留在一个地方。迁徙是它们生活中很正常的一部分。有些动物迁移是为了更容易找到食物，而有些则是为了远离拥挤的地方，或者是为了在地震等灾难中存活下来。我们可以把这种行为与人们为了获得更好的机会而搬家相比较。
Some fishes give birth in warm water and move to cold water to feed. The most famous migration is probably that of the fish called “salmon”. This fish is usually grey, but turns red when it is ready to breed. It is born in fresh water but travels miles to salt water. They must fight against the strong force of the river and avoid being hunted by bears, because the law of nature allows only the strongest salmon to survive. When it is old, it returns to its birthplace in fresh water. Then it gives birth and dies.
有些鱼类在温暖的水域产卵，然后游到冷水域觅食。其中最著名的迁徙可能是一种叫“鲑鱼”的鱼类。这种鱼通常是灰色的，但在准备交配繁殖时会变成红色。它们出生在淡水中，却要跋涉数英里来到海水中。它们必须对抗河流的强大力量，还要躲避熊的捕食，因为自然法则只允许最强壮的鲑鱼存活。当它们年老时，会返回到出生地的淡水中，在那里产卵，然后死去。
In the north of Europe, there is a kind of mouse. They usually look pale, but when their homes become crowded, their colour gets brighter. They have a crazy way of moving. Sometimes they move all the way to the seaside, forming large groups like an army. Many of them are killed when they fall into the sea.
在欧洲北部有一种老鼠，它们的毛色通常较淡，但当它们的栖息地变得拥挤时，其毛色就会变得更鲜艳。它们的迁徙方式有些疯狂。有时，它们会一路迁徙到海边，成群结队地前进，就像军队一样。它们中有许多会掉入海里丧生。
Recently, scientists have studied a special kind of lobsters. 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, just like soldiers marching. Nobody knows where they go.
最近，科学家研究了一种特殊的龙虾。每年天气恶劣的季节来临时，这些龙虾会排成长队，开始在海底行走，就像士兵行军一样。没有人知道它们要去哪里。
The reason why animals move may vary. Maybe living things just like to travel.
动物迁徙的原因可能各不相同。也许生物就是喜欢“旅行”。