Grizzly bears, which may grow to about 2.5 m long and weigh over 400 kg, occupy a conflicted corner of the American psyche — we revere (敬畏) them even as they give us frightening dreams. Ask the tourists from around the world that flood into Yellowstone National Park what they most hope to see, and their answer is often the same: a grizzly bear. 

"Grizzly bears are re-occupying large areas of their former range, " says bear biologist Chris Servheen. As grizzly bears expand their range into places where they haven't been seen in a century or more, they're increasingly being sighted by humans.

The western half of the US was full of grizzlies when Europeans came, with a rough number of 50, 000 or more living alongside Native Americans. By the early 1970s, after centuries of cruel and continuous hunting by settlers, 600 to 800 grizzlies remained on a mere 2 percent of their former range in the Northern Rockies. In 1975, grizzlies were listed under the Endangered Species Act. 

Today, there are about 2, 000 or more grizzly bears in the US. Their recovery has been so successful that the US Fish and Wildlife Service has twice attempted to delist grizzlies, which would loosen legal protections and allow them to be hunted. Both efforts were overturned due to lawsuits from conservation groups. For now, grizzlies remain listed. 

Obviously, if precautions (预防) aren't taken, grizzlies can become troublesome, sometimes killing farm animals or walking through yards in search of food. If people remove food and attractants from their yards and campsites, grizzlies will typically pass by without trouble. Putting electric fencing around chicken houses and other farm animal quarters is also highly effective at getting grizzlies away. "Our hope is to have a clean, attractant-free place where bears can pass through without learning bad habits, " says James Jonkel, longtime biologist who manages bears in and around Missoula.