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In the past 300 years, more than 130 species of animals have becomeextinct. One of these extinct species is the passenger pigeon (鸽子). At one time there were millions of these birds in North America, but now there are none. The last one died in Cincinati Zoo in 1914. Another extinct animal is the cape lion. This animal has been extinct since 1860.

What causes animals to become extinct? Too much hunting is one cause. Pollution is another.

Governments around the world have begun to protect endangered animals that could become extinct. In the United States, the Fish and Wildlife Service is responsible (负责) for endangered animals. It has listed nearly 200 endangered species in North America.