英语听力文摘 English Digest 689 杀手猫：猫每年杀死37亿只禽类（在线收听）

Killer Cats: Cats Kill Up To 3.7 Billion Birds Each Year

It’s time to go again to the A Moment of Science mailbag. A listener writes:

Dear A Moment of Science,

I know that cats kill a lot of wild birds and other animals. But as a cat owner and cat lover I can’t help but be a little defensive. And I wonder: don’t other pets kills wild animals, too?

Killer Cats

Yes, they do. In fact, after cats, one of the main culprits when it comes to harming wildlife is none other than man’s best friend: dogs.

Cats in the United States kill up to 3.7 billion birds every year and as many as 20 billion small mammals. And many cats roam free while dogs are either kept on leashes or in fenced yards. So how can dogs possibly do as much damage as cats?

Dogs vs Cats

Well, dogs don’t kill as many animals as cats, especially not in the United States. But consider that in many other countries dogs are not kept fenced in. Experts estimate that around 75% of dogs around the world are free roamers.

And when given free reign, dogs rack up their share of kills. For example, in the 1980s researchers found that a single stray dog in New Zealand killed as many as 500 flightless birds called Kiwis. In 2006, a small pack of owner-less dogs on Viwa Island in the South Pacific came close to wiping out a species of ground frog.

The point is that cats are not the only culprits. Any ecosystem is vulnerable when a foreign species without natural predators invades.

杀手猫：猫每年杀死37亿只禽类

又到了“科学时刻”邮袋的时候了。听众写道：

亲爱的科学时刻：

我知道猫会杀死很多野生鸟类和其他动物。但作为一个猫主人和爱猫的人，我忍不住要有点防备。我想知道：难道其他宠物也会杀死野生动物吗？

杀手猫

是的，他们有。事实上，除了猫，伤害野生动物的罪魁祸首之一就是人类最好的朋友：狗。

美国的猫每年杀死多达37亿只鸟类和多达200亿只小型哺乳动物。许多猫自由自在地漫步，而狗要么被拴在皮带上，要么被关在围栏里。那么，狗怎么可能造成和猫一样多的伤害呢？

狗vs猫

嗯，狗杀死的动物不如猫多，尤其是在美国。但想想看，在许多其他国家，狗没有被关在围栏里。专家估计，全世界大约75%的狗是自由流浪者。

当狗被自由支配时，它们的猎物也会增加。例如，在20世纪80年代，研究人员发现，新西兰的一只流浪狗杀死了多达500只不会飞的鸟，称为奇异鸟。2006年，在南太平洋的维瓦岛上，一小群没有主人的狗几乎消灭了一种地蛙。

重点是猫不是唯一的罪魁祸首。当没有天敌的外来物种入侵时，任何生态系统都是脆弱的。