20 Why Do They Do It?

Why would an animal commit suicide? It seems a strange question and yet it is one that has intrigued some people for a long time. For there is a kind of rodent, called the lemming that periodically commits mass suicide, and no one knows just why.

The small creatures which inhabit the Scandinavian mountains, when their food supply is sufficiently large, the lemmings live a normal, undisturbed, rodent life.

However, when the lemmings' food supply becomes too low to support the population, a singular migration commences. The lemmings begin a trek across the mass, forming huge hordes. (Great numbers of the rodents devour every Scandinavian plains, a journey that may last weeks. The lemmings march until they reach the sea.

Upon reaching the coast, the following their destructive march, the reason for the journey becomes clear. Most say afoot only a short time before they tire, swim by the thousands into the surf. The lemmings remain an enigma for zoologists and naturalists.

A common theory for this mass suicide is that the lemmings do not realize that the ocean is such a huge body of water. In their cross-country journey, the animals must traverse many smaller bodies of water such as rivers and small lakes. They may assume that the sea is just another such swimmable obstacle. But no final answer has been found to the mystery.

20 它们为何这么做？

动物为什么会自杀？这似乎是个奇怪的问题，但长期以来一直困扰着一些人。因为有一种叫旅鼠的啮齿动物会周期性地集体自杀，而没人知道确切原因。

这些生活在斯堪的纳维亚山脉的小动物，在食物供应充足时，过着正常、安稳的啮齿动物生活。

然而，当旅鼠的食物供应少到无法维持种群数量时，一场特殊的迁徙就开始了。旅鼠们成群结队地穿越陆地，形成庞大的兽群。（大量旅鼠会吞噬斯堪的纳维亚平原上的一切，这场迁徙可能持续数周。它们一直行进，直到抵达海边。

到达海岸后，在这场破坏性的迁徙之后，它们旅程的目的变得清晰起来。大多数旅鼠在疲惫前只走了一小段路，然后成千上万地游进海浪里。旅鼠对动物学家和博物学家来说仍然是个谜。

关于这种集体自杀的一个常见理论是：旅鼠没有意识到海洋是如此巨大的水域。在穿越陆地的旅程中，它们必须渡过许多较小的水域，比如河流和小湖泊。它们可能以为海洋只是另一个可以游过去的障碍。但这个谜团至今没有确切的答案。