A prairie dog stands at a burrow on the Buffalo Gap National Grasslands in South Dakota on July 14. Wildlife officials are working to protect prairie dogs and endangered black-footed ferrets from the plague that has hit the area.

Interior, S.D. ? On the grasslands a few miles from the pinnacles and spires of Badlands National Park, federal wildlife officials have been waging a war since spring to save one of the nation’s largest colonies of endangered black-footed ferrets.

The deadly disease sylvatic plague was discovered in May in a huge prairie dog town in the Conata Basin. The black-tailed prairie dog is the main prey of ferrets, and the disease quickly killed up to a third of the area’s 290 ferrets along with prairie dogs.

The disease stopped spreading with the arrival of summer’s hot, dry weather, but it poses a serious threat to efforts to establish stable populations of one of the nation’s rarest mammals, said Scott Larson of the U.S. Fish and Wildlife Service in Pierre.

The plague, which is carried by fleas, is the biggest danger to ferrets’ survival in the Conata Basin and other sites that still have ferrets, said Larson, who is coordinating ferret conservation efforts among five federal agencies.

“It has the capacity to take out more ferret habitat than anything we’ve run up against, and do it in such a short order,” Larson said. “For ferrets, it’s the most challenging issue we face.”

The ferrets were once considered extinct. But one colony was discovered in Wyoming in 1981, and a captive breeding program succeeded in increasing their numbers. Since then, ferrets have been reintroduced at 17 sites in South Dakota, Wyoming, Montana, Colorado, Utah, Kansas and Mexico, said Nancy Warren, endangered species program leader in the Rocky Mountain Region of the U.S. Forest Service.

Reintroduction efforts failed in some locations, and plague has hit most of the ferret colonies to some degree, Larson said.

Establishing many reintroduction sites helps protect the overall ferret population from being wiped out by plague, Larson said. “I guess it’s the old risk management of having your eggs spread out among many baskets.”

Representatives of federal agencies and some conservation groups have taken a double-barreled approach to try to stop the spread of plague and save prairie dogs and ferrets in the 20-mile-long Conata Basin, a portion of the Buffalo Gap National Grasslands that lies just south of the Badlands in southwestern South Dakota.

This summer, a crew of four has buzzed across the prairie on all-terrain vehicles, pausing frequently to spray white insecticide dust into prairie dog burrows to kill fleas.

After dark, another crew moved into the area during part of the summer to shine spotlights across the grasslands, trap ferrets and vaccinate them against the plague.

Officials want to dust about 11,000 acres with insecticide by this fall, and have covered about two-thirds of that area so far. More than 60 ferrets have been vaccinated, with 15 of them already getting the desired two doses.

Of the 25,000 acres of prairie dog habitat managed for ferrets in the basin, the plague had spread to about 9,700 acres before its growth halted in August. Officials expect the plague might start spreading again this fall or next spring. The disease has not been found inside Badlands National Park itself.

Warren said the insecticide appears to be effective, but it’s too early to tell whether it will save the ferrets.

“We’re learning as we go. We really don’t know the answer to that yet,” Warren said. “We’re hopeful with the dusting, which is something new we’re doing now, we’ll be able to at least contain the extent of this plague.”