1OK, so we've been looking at how man-made changes in our environment can affect wildlife.
2Now I'll discuss a particular example.
3Let's take a look at mercury.
4Mercury's one of the 120 or so elements that make up all matter,
5and it has the symbol Hg.
6It's a shiny, silvery substance.
7You may have seen it in old-fashioned thermometers,
8but it's not used much for domestic purposes now
9because it's highly toxic.
10But the problem is that the amount of mercury in the environment's increasing.
11The main reason for this is the power plants used to produce electricity.
12The main source of energy that most of them use is still coal,
13and when it's burned it releases mercury into the atmosphere.
14Some of this gets deposited into lakes and rivers,
15and if it's ingested by a fish it's not excreted,
16it stays in the fish's body and it enters the food chain.
17So it's been known for some time that birds which eat fish may be affected,
18but what wasn't known until quite recently is that those that eat insects can also be affected.
19So a woman called Claire Varian-Ramos is doing some research on how this is affecting birds.
20And rather than looking at how many birds are actually killed by mercury poisoning,
21she's looking for more subtle sub-effects.
22And these may be to do with the behaviour of the birds,
23or with the effect of mercury on the way their brain works,
24so whether it leads to problems with memory, for example.
25And she's particularly focusing on the effects of mercury on bird song.
26Now, the process of song learning happens at a particular stage in the birds' development,
27and what you may not know
28is that a young bird seems to acquire this skill by listening to the songs produced by its father,
29rather than by any other bird.
30And Varian-Ramos has already found in her research
31that if young male birds are exposed to mercury,
32if they eat food contaminated with mercury,
33then the songs they produce aren't as complex as those produced by other birds.
34So quite low-level exposure to mercury is likely to have an impact on male birds in a natural situation,
35because it can mean that they're less attractive to female birds,
36and so it can affect their chances of reproduction.
37Now the way she's carrying out this research is worth thinking about.
38She's using a mixture of studies using birds kept in laboratories,
39and studies carried out outdoors in the wild.
40The lab-based studies have the advantage that you don't get all the variables you would in a natural setting,
41so the experimenter has a much higher level of control,
42and that means they can be more confident about their results in some ways.
43And of course they don't have to worry about going out and finding the birds in order to observe them.
44So what are the implications here for humans?
45Well, because many birds are migratory,
46they may be transporting mercury far from contaminated sites.
47For example, it's been found that ducks who'd been feeding at a contaminated site
48were later shot by hunters over a thousand kilometres away,
49and presumably eaten.
50But these birds likely had mercury levels high enough to warrant concern for human consumption.
51In addition, going back to song learning by birds,
52we saw that this may be affected by mercury contamination.
53Well, we also know that in humans,
54mercury causes developmental delays in the acquisition of language,
55and in fact this process is very similar in the brain regions it involves
56and even the genes that are involved.
57But mercury contamination has other important implications for humans as well.
58It's now known that an unborn child can be affected
59if the food eaten by its mother contains high levels of mercury,
60and these effects can be quite substantial.
61In the end, it comes down to whether more value is placed on human economic wellbeing or environmental wellbeing.
62It's true there are new regulations for mercury emissions from power plants,
63but these will need billions of dollars to implement,
64and increase costs for everyone.
65Some argue that's too much to pay to protect wildlife.
66But as we've seen, the issues go beyond that,
67and I think it's an issue we need to consider very carefully.