The black-footed ferrets reintroduced into Wind Cave National Park a year ago have produced at least three litters of babies, a sign the program is on the right track, officials said Friday.

Fourteen baby ferrets, known as kits, were trapped and released recently in four nights of surveying, Park superintendent Vidal Davila said. The kits are the offspring of some of the 49 adult ferrets released last year in the park, which is located in the southern Black Hills in southwest South Dakota.

Duane Weber, a biological technician in the park, said officials do not know how many ferrets are in the park, but the presence of kits indicates the reintroduction is going well. Black-footed ferrets, one of North America's rarest mammals, had not been seen in Wind Cave National Park for three decades before last year's reintroduction.

"The real exciting part was to have that number of kits captured," Weber said.

Crews who trapped the 14 kits also captured four adults and saw another 10 or so adults, Weber said. The babies were captured in three widely separated prairie dog towns, indicating they were born in separate litters, he said.

Prairie dogs are the main prey of black-footed ferrets.

A crew from the National Park Service, the U.S. Fish and Wildlife Service and a contractor trapped the baby ferrets. They implanted a microchip in the animals for identification, drew blood, checked for fleas and vaccinated each kit for distemper before releasing the babies.

Davila said crew members walked 10 to 15 miles a night looking for ferrets in the park's prairie dog towns.

The ferrets were once considered extinct. But after a colony was discovered in Wyoming in 1981, a captive breeding program succeeded. Wind Cave is one of 17 sites where the endangered species has been reintroduced.

Reintroduction efforts have failed in some locations, and plague has killed prairie dogs and ferrets in some areas.

Weber said officials will decide each year whether they need to release more ferrets at Wind Cave, but they decided not to release any this year because the existing population appears to be doing well. The main source for ferrets to be reintroduced has been the Conata Basin near Badlands National Park, and that area has been hit by plague, so no ferrets have been captured there for release this year, he said.

There has been no hint of plague in Wind Cave National Park, but crews have been spraying insecticide dust into prairie dog holes in the last two months to try to prevent an infestation.

Tom Farrell, chief of interpretation at Wind Cave, said the park's goal is to have 30 reproducing females at the end of five years. The 14 kits trapped recently shows the park is making progress toward that goal, he said.

Most visitors to Wind Cave don't see ferrets because the animals are nocturnal, Farrell said. "People are very interested in the ferrets. They haven't seen a lot of them, but it's definitely a topic of conversation here."

The park held 15 or more nighttime hikes led by rangers through prairie dog towns this summer, and only one group saw ferrets, Farrell said. But other groups saw the stars and other wildlife, including a herd of 100 elk, he said.

"People just had a blast," Farrell said.