| OK, so we've been looking at how man-made changes in our environment can affect wildlife. |
| Now I'll discuss a particular example. |
| Let's take a look at mercury. |
| Mercury's one of the 120 or so elements that make up all matter, |
| and it has the symbol Hg. |
| It's a shiny, silvery substance. |
| You may have seen it in old-fashioned thermometers, |
| but it's not used much for domestic purposes now |
| because it's highly toxic. |
| But the problem is that the amount of mercury in the environment's increasing. |
| The main reason for this is the power plants used to produce electricity. |
| The main source of energy that most of them use is still coal, |
| and when it's burned it releases mercury into the atmosphere. |
| 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. |
| 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. |
| So a woman called Claire Varian-Ramos is doing some research on how this is affecting birds. |
| And rather than looking at how many birds are actually killed by mercury poisoning, |
| she's looking for more subtle sub-effects. |
| 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. |
| And she's particularly focusing on the effects of mercury on bird song. |
| 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. |
| 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. |
| 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. |
| Now the way she's carrying out this research is worth thinking about. |
| She's using a mixture of studies using birds kept in laboratories, |
| and studies carried out outdoors in the wild. |
| 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. |
| And of course they don't have to worry about going out and finding the birds in order to observe them. |
| So what are the implications here for humans? |
| Well, because many birds are migratory, |
| they may be transporting mercury far from contaminated sites. |
| 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. |
| But these birds likely had mercury levels high enough to warrant concern for human consumption. |
| In addition, going back to song learning by birds, |
| we saw that this may be affected by mercury contamination. |
| 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. |
| But mercury contamination has other important implications for humans as well. |
| 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. |
| In the end, it comes down to whether more value is placed on human economic wellbeing or environmental wellbeing. |
| 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. |
| Some argue that's too much to pay to protect wildlife. |
| But as we've seen, the issues go beyond that, |
| and I think it's an issue we need to consider very carefully. |