英语听力：探索发现 2013-02-17 猛玛象进城记 Mammoths to Manhattan—9

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Meanwhile increasing numbers of the tame horses escaped into the wild. These feral horses became known by the Spanish name, mustang. They put extra pressure on the dwindling³ bison numbers by competing for their grazing sites and drinking holes. 

 

Mustangs form social groups led by a dominant⁴ stallion, echoing their prehistoric⁵ relatives that lived here during the Ice Age. 

 

Bred to carry the weight of a rider, mustangs are larger than those early wild horses, but they still display the same kind of behavior. 

 

By the early 1800s, the wild horse was well and truly back in North America, but how did other wildlife on the continent survive alongside growing human populations?

 

Some wild creatures did the reverse of mustangs by becoming tame and choosing to live close to people. The purple martin became an unofficial mascot⁶ for native inhabitants in the eastern half of the continent. Here people erected⁷ special nesting sites to encourage the birds to stay.

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