英语听力：猛玛象进城记—17

But there is at least one place in Florida where the manatees benefit from humans being around. Clean, hot water released from this power plant turns a man-made inlet into a hot tub. And during winter months when sea temperatures drop below 20 degrees centigrade, manatees gather here to keep warm. It’s actually an artificial version of the natural hot springs where manatees traditionally congregate. But this particular location seems to be extremely popular. During the coldest spells, more than 300 manatees can gather here.

With so many of these shy creatures in one place, the power plant has become a tourist attraction. It may not be the most scenic setting, but this is a unique chance to see one of the largest gatherings of manatees in the world.

People have become dependent on industry to support their modern lifestyle, so too it seems has some of North America’s wildlife. Every September, the skies over Portland, Oregon become crowded with vaux's swifts. These birds have chosen a 30-meter chimney stack as a place to roost. Tens of thousands funnel down into the disused chimney where they huddle together for the night. Vaux's swifts traditionally roost communally in the hollow trees, but as many of North America’s forests are destroyed, they've turned to man-made structures.