One of the nation's largest colonies of endangered black-footed ferrets is surviving despite the disease that has hit their home in a vast stretch of prairie dog towns south of Badlands National Park.

Since the sylvatic plague was discovered in South Dakota's Conata Basin in May 2008, the disease has wiped out black-tailed prairie dogs, the ferrets' main prey, in about half their former range. However, many of the ferrets have been protected by efforts to vaccinate them and to stop the spread of the disease by dusting with insecticide that kills the fleas that carry the plague.

The black-footed ferret was once considered extinct, but a captive breeding program succeeded after a colony was discovered in Wyoming in 1981. Since then, ferrets have been reintroduced at sites in South Dakota, Wyoming, Montana, Colorado, Utah, Kansas and Mexico.