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Why do some animals die out?
In the past two hundred years people have caused many kinds of animals to die out--to become extinct. People keep building houses and factories in fields and woods. As they spread over the land, they destroy animals' homes. If the animals can't find a place to live, they die out. Sixteen kinds of Hawaiian birds have become extinct for this reason. Other animals, such as the Florida Key deer, may soon die out because they are losing their homes. Hunters have caused some animals to become extinct, too. In the last century, hunters killed all the passenger pigeons in North America and most of the buffalos.
Today they are fast killing off hawks and wolves. Pollution is killing many animals today, too. As rivers become polluted, fish are poisoned. Many die. Birds that eat the poisoned fish can't lay strong, healthy eggs. New birds aren’t born. So far, no animals have become extinct because of pollution. But some, such as the bald eagle and the brown pelican, have become rare and may die out.
Scientists think that some animals become extinct because of changes in climate. The places where they live become hotter or cooler, drier or wetter. The food that they eat cannot grow there any more. If the animals can't learn to eat something else, they die. Dinosaurs may have died out for this reason.
In the past two hundred years, many kinds of animals have died out. There are several reasons for it. First, people keep building houses and factories in fields and woods, which destroys animals' homes. Then, hunters' killing has also caused some animals to become extinct. Besides, some animals aren't able to bear strong offspring and nor do they have enough food to eat because of pollution and climatic changes.