IELTS Listening · Cam 12

Test 3 Part 4

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

Level: C1 · 88 sentences

Transcript

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