OK, so we've been looking at how man-made changes in our environment can affect wildlife.
好了，我们一直在研究人类造成的环境改变是如何影响野生动物的。
Now I'll discuss a particular example. Let's take a look at mercury.
现在来讨论一个特别的例子。我们来看一下汞。
Mercury's one of the 120 or so elements that make up all matter, and it has the symbol Hg.
汞是组成所有物质的120多种元素之一，它的符号是Hg.
It's a shiny, silvery substance.
它是一种有光泽的、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.
你也许在老式的温度计中见过它，但由于其强烈毒性，现在用于家庭用途已不多。
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在上升。
The main reason for this is the power plants used to produce electricity.
造成这一问题的主要原因是发电厂要使用它来发电。
The main source of energy that most of them use is still coal, and when it's burned it releases mercury into the atmosphere.
大多数发电厂的能量来源仍然是煤，当煤燃烧时会释放汞到大气中。
Some of this gets deposited into lakes and rivers,
有一些汞会沉淀到河湖中，
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.
如果被鱼吸收而没有排泄出来，就会残留在鱼体内，从而进入食物链。
So it's been known for some time that birds which eat fish may be affected,
食鱼的鸟可能会受影响这一点为人所知已有一段时间，
but what wasn't known until quite recently is that those that eat insects can also be affected.
但直到最近才为人知的是那些吃昆虫的鸟也会受到影响。
So a woman called Claire Varian-Ramos is doing some research on how this is affecting birds.
一位叫做Claire Varian-Ramos正在研究这是如何影响鸟类的。
And rather than looking at how many birds are actually killed by mercury poisoning, she's looking for more subtle sub-effects.
她并没有看有多少鸟是汞中毒而亡的，而是研究更微妙的亚作用。
And these may be to do with the behaviour of the birds or with the effect of mercury on the way their brain works,
这一切可能跟鸟类的行为或是汞对大脑工作的影响有关，
so whether it leads to problems with memory, for example.
所以比如说它会不会导致记忆问题呢。
And she's particularly focusing on the effects of mercury on bird song.
Varian-Ramos尤其关注汞对鸟类鸣叫的影响。
Now the process of song learning happens at a particular stage in the birds' development,
学习鸣叫的过程发生在鸟类成长中的一个特定阶段，
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,
你们可能不知道的是幼鸟似乎是通过聆听其父亲的鸣叫习得这项技能的，
rather than by any other bird.
而不是通过其他的鸟。
And Varian-Ramos has already found in her research that if young male birds are exposed to mercury,
Varian-Ramos已经在其研究中发现如果幼年雄鸟暴露于汞中，
if they eat food contaminated with mercury, then the songs they produce aren't as complex as those produced by other birds.
或是吃了受汞污染的食物，那它们发出的鸣叫声就不有其他鸟发出的那样复杂。
So quite low-level exposure to mercury is likely to have an impact on male birds in a natural situation,
所以在自然条件下，相当轻微地暴露于汞中可能对雄鸟产生影响，
because it can mean that they're less attractive to female birds, and so it can affect their chances of reproduction.
因为那可能意味着他们对雌鸟的吸引力较差，这就会影响到它们的繁殖机会。