英语听力：探索发现 2012-11-16 美洲大平原 American Serengeti—9

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Smaller grazers are still found here, too.  But they stay put instead of wandering the plains. Prairie dogs inhabit rambling³ subterranean⁴ towns that stretch tens of square miles. These highly social creatures stay within a short dash of their door, ready to retreat from predators⁵ or by weather.  It’s always maintenance work to do, but major renovations have to wait until after rain when the soil is soft.  All this working and re-working helps the land recover from the impact of so many bigger feet and appetites. 

 

At summer's end, male bison help to move the sun-baked soil as the rutting season starts. They roll in dust and paw the ground to try to dominate their rivals. The dust bath also helps to dislodge irritating insects. 

 

A prairie dog colony is usually surrounded by short, nutritious⁶ grass, thanks to the many teeth and toe. This constant grazing stimulates⁷ fresh growth and also keeps the field of vision clear for spotting predators. Larger neighbours are attracted to these burgeoning⁸ meadows, just as they were 13,000 years ago.

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