OK, so we've been looking at how man-made changes in our environment can affect wildlife.

好了，我们已经看到环境中人类的变化是如何影响野生动物的了。

Now I'll discuss a particular example.

现在我要讨论一个具体的案例。

Let's take a look at mercury.

让我们来看一下汞元素。

Mercury's one of the 120 or so elements that make up all matter, and it has the symbol Hg.

汞是我们所需的120种元素之一,而且它的符号是Hg。

It's a shiny, silvery substance.

它是种发光的，银色的物质。

You may have seen it in old-fashioned thermometers, but it's not used much for domestic purposes now because it's highly toxic.

你可能在老式温度计上看到过它，但它现在已经不大作为家庭用途了，因为它有剧毒。

But the problem is that the amount of mercury in the environment's increasing.

但问题是环境中的汞含量不断增加。

The main reason for this is the power plants used to produce electricity.

主要原因就是发电站用来发电。

The main source of energy that most of them use is still coal, and when it's burned it releases mercury into the atmosphere.

发电站使用的能量来源主要是煤炭，当煤炭燃烧时就会释放出汞，进入到空气中。

Some of this gets deposited into lakes and rivers, and if it's ingested by a fish it's not excreted, it stays in the fish's body and it enters the food chain.

一些汞进入到湖里和河里，并且被鱼食用，导致无法从体内排出，因此进入到食物链中。

So it's been known for some time that birds which eat fish may be affected, but what wasn't known until quite recently is that those that eat insects can also be affected.

因此我们了解到一些鸟吃了这些鱼之后就会被影响，但我们最近才知道的是那些吃了昆虫的鸟也会被影响到。

So a woman called Claire Varian-Ramos is doing some research on how this is affecting birds.

有一个叫克莱尔·拉莫斯瓦里安的女性正在进行一项关于这会如何影响到鸟类的研究。

And rather than looking at how many birds are actually killed by mercury poisoning, she's looking for more subtle sub-effects .

她没有把重点放在有多少鸟死于汞中毒，而是把注意力放在更细微的副作用上。

And these may be to do with the behaviour of the birds, or with the effect of mercury on the way their brain works, so whether it leads to problems with memory, for example.

这个可能和鸟的行为有关，或者和汞对大脑运行的影响有关，比如它是否对记忆问题有影响。

And she's particularly focusing on the effects of mercury on bird song.

她尤其关注汞对鸟鸣的影响。

Now, the process of song learning happens at a particular stage in the birds' development, and what you may not know is that a young bird seems to acquire this skill by listening to the songs produced by its father, rather than by any other bird.

鸟类学习鸣叫的过程发生在特别的成长阶段，并且你可能不知道的是一只幼鸟是通过听它父亲鸣叫来习得这种技能的，而不是通过其他鸟类。

And Varian-Ramos has already found in her research that if young male birds are exposed to mercury, if they eat food contaminated with mercury, then the songs they produce aren't as complex as those produced by other birds.

拉莫斯瓦里安已经在她的研究中发现如果年轻的雄鸟暴露在汞的环境中，如果它们食用了含有汞的食物，那他们的鸣叫就没有其他鸟那么多样。

So quite low-level exposure to mercury is likely to have an impact on male birds in a natural situation, because it can mean that they're less attractive to female birds, and so it can affect their chances of reproduction.

因此，在自然环境中，接触少量汞很可能对雄鸟有一定的影响，因为这意味着它们对雌鸟的吸引力下降，继而影响它们繁殖的机会。

Now the way she's carrying out this research is worth thinking about.

现在，她开展研究的方式也值得思考。

She's using a mixture of studies using birds kept in laboratories, and studies carried out outdoors in the wild.

她运用了混合研究，既使用了实验室里的鸟进行研究，也在户外野生环境下开展研究。

The lab-based studies have the advantage that you don't get all the variables you would in a natural setting, so the experimenter has a much higher level of control, and that means they can be more confident about their results in some ways.

实验室研究的好处是，它没有在自然背景下研究会存在的诸多变量，因此，实验能够在更加可控的状况下进行，这也意味着在某种程度上他们对研究成果更加自信。

And of course they don't have to worry about going out and finding the birds in order to observe them.

当然了，他们也不用担心要去到户外找到一些鸟类来观察。

So what are the implications here for humans?

那这对人类的暗示是什么呢？

Well, because many birds are migratory, they may be transporting mercury far from contaminated sites.

由于许多鸟都是迁徙而来的，他们可能会从污染地携带汞而来。

For example, it's been found that ducks who'd been feeding at a contaminated site were later shot by hunters over a thousand kilometres away, and presumably eaten.

比如说，在污染地喂食的鸭之后被千米以外的猎人猎杀并很可能被吃掉。

But these birds likely had mercury levels high enough to warrant concern for human consumption.

但是这些很可能含汞超量的鸟足以对人类消费造成威胁。

In addition, going back to song learning by birds, we saw that this may be affected by mercury contamination.

除此之外，回到刚才说的鸟鸣的习得，我们看到这个可能会被汞污染所影响。

Well, we also know that in humans, mercury causes developmental delays in the acquisition of language, and in fact this process is very similar in the brain regions it involves and even the genes that are involved.

我们也知道对人类来说，汞会造成语言习得的延缓，事实上，这个过程在所涉及到的人脑区域甚至基因都非常相似。

But mercury contamination has other important implications for humans as well.

但是汞污染也对人类有其他重要的启发。

It's now known that an unborn child can be affected if the food eaten by its mother contains high levels of mercury, and these effects can be quite substantial.

现在我们知道，如果妈妈食用了富含汞的食物，未出世的小孩会受到极大影响，而这些影响是异常深远的。

In the end, it comes down to whether more value is placed on human economic wellbeing or environmental wellbeing.

最后，又回到了应该侧重经济发展还是环境发展的问题。

It's true there are new regulations for mercury emissions from power plants, but these will need billions of dollars to implement, and increase costs for everyone.

确实有新的规定制约发电厂的汞排放问题，但是这需要数十亿美元的支持，也加大了成本。

Some argue that's too much to pay to protect wild life.

有人认为为了保护环境付出的代价太大了。

But as we've seen, the issues go beyond that, and I think it's an issue we need to consider very carefully.

但我们可以看到，问题远远超出了这些，并且我认为这是我们必须认真思考的问题。