Population decline in US birds



In the past century, the steady growth of the human population and the corresponding increase in agriculture and pesticide use have caused much harm to wildlife in the United States—birds in particular. Unfortunately for birds, these trends are likely to continue, with the result that the number of birds in the United States will necessarily decline.

First, as human populations and settlements continue to expand, birds' natural habitats will continue to disappear. Forests, wetlands, and grasslands will give way to ever more homes, malls, and offices. As the traditional areas suitable for birds keep decreasing, so will the size of the bird populations that depend on those vanishing habitats.

Second, agricultural activities must increase to keep pace with the growing human population. The growth of agriculture will also result in the further destruction of bird habitats as more and more wilderness areas are converted to agricultural use. As a result, bird populations in rural areas will continue to decline.

Third, as human settlements expand and agriculture increases, the use of chemical pesticides will also increase. Pesticides are poisons designed to kill agricultural and home garden pests, such as insects, but inevitably, pesticides get into the water and into the food chain for birds where they can harm birds. Birds that eat the poisoned insects or drink contaminated water can die as a result, and even if pesticides do not kill birds outright, they can prevent them from reproducing successfully. So pesticides have significantly contributed to declines in bird population, and because there will continue to be a need to control agricultural pests in the future, this decline will continue.

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Now listen to part of a lecture on the topic you just read about.

The passage claims that there will be fewer and fewer birds, but the arguments used to support this claim are unconvincing.

First, it's true that urban growth has been bad for some types of birds, but urban development actually provides better and larger habitats for other types—so much so that city and suburban dwellers often complain about increased bird populations: seagulls at land fills, pigeons on the streets, and so on. Even birds like hawks and falcons can now be found in cities, where they prey on the increasing populations of pigeons and rodents. So it's not going to be a story of uniform decline of bird populations in the future—some populations may shrink but others will grow.

As for agriculture—it's true that it too will increase in the future—but not in the way assumed by the reading passage. The truth is, in the United States less and less land is being used for agriculture every year. Increases in agricultural production have resulted from, and will continue to result from, the introduction of new, more productive varieties of crops. These new crops produce more food per unit of land, and as a result there's no need to destroy wilderness areas.

Third, while it's certainly true that traditional pesticides have been destructive to birds, it's incorrect to project this history into the future. Now that people are aware of the possible consequences of traditional pesticides, two changes have occurred: first, new and much less toxic pesticides are being developed and that's important. Second, and perhaps more importantly, there is a growing trend to develop more pest-resistant crops—crops that are genetically designed to be unattractive to pests. Pest-resistant crops greatly reduce the need for chemical pesticides, and best of all, pest-resistant crops don't harm birds at all.


Summarize the points made in the lecture, being sure to explain how they challenge the specific points made in the reading passage.



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