RAPID CITY, S.D. (AP) - While black-footed ferrets have made a strong comeback in South Dakota, their recovery still faces an uphill battle nationwide, a federal official said.

Black-footed ferrets were thought to be extinct until 18 of them were discovered near Meeteetse, Wyo., about 20 years ago.

Today, nearly 500 of the animals live in the wild, with the majority of them at three sites in South Dakota, said Mike Lockhart, coordinator of the Black-Footed Ferret Recovery program for the U.S. Fish & Wildlife Service.

A main site for ferrets in South Dakota is the Conata Basin south of Badlands National Park, one of the most successful reintroduction sites in the country, said Lockhart.

But ferret recovery remains a fight, said Lockhart and other scientists who presented a Saturday workshop on managing black-footed ferrets and prairie dogs in Conata Basin.

"Yes, technically, we think its certainly feasible and we think its worthwhile to pursue continued recovery efforts," said Lockhart.

But if current conditions dont change, long-term ferret recovery is not feasible, he added.

Just getting the ferret off the federal endangered species list will require at least 10 separate sites with self-sustaining populations and at least 1,500 animals, Lockhart said in an interview.

Conata Basin is a self-sustaining sites and there is possibly a second on the Cheyenne River Indian Reservation, said Lockhart. A third reintroduction site, on the Rosebud Indian Reservation, also looks promising, Lockhart said.

The 2004 ferret population survey listed 206 ferrets at Conata Basin, 67 on Cheyenne River and 33 at Rosebud.

However, reintroduction in Montana and elsewhere has not been as successful in part because of sylvatic plague, said Randy Matchett of the USF&WS in Montana. Plague hasn't hit the South Dakota sites.

Scientists are testing a vaccine against plague. But because of costs, even a successful vaccine would be merely a "finger in the dike," Matchett said.

David McDonald of the University of Wyoming said mathematical analysis shows that black-footed ferrets can proliferate quickly but are vulnerable to external conditions and can "blink out" just as quickly.

A key to ferret recovery is developing large prairie dog complexes that encompass several thousand acres each, experts said. Ferrets depend on prairie dogs as their sole source of food.

But many ranchers in Conata Basin and elsewhere in southwest South Dakota don't want more prairie dogs. They say proliferating populations of prairie dogs have destroyed the grass on the national grasslands where they have livestock grazing permits and have encroached onto their private land as well.

Lockhart said black-footed ferrets and prairie dogs can coexist in normal conditions with livestock grazing and other uses of public land.

He also said those working to bring the ferret back need to do a better job minimizing damage from prairie dogs to adjoining private land.

"If there are landowners who don't want prairie dogs on their land, they shouldnt be there."