RAPID CITY, S.D. -

 South Dakota's Wind Cave National Park has nine more of one of the rarest mammals in North America, following the release this week of nine black-footed ferret kits.
    
The ferrets were born in captivity at the U.S. Fish and Wildlife Service National Black-footed Ferret Conservation Center in Colorado.
    
It's the third time the park has augmented its black-footed ferret population since re-establishing a population in 2007. The release is part of an ongoing effort to bring the endangered ferrets back from the brink of extinction.
    
It's not known exactly how many ferrets are in the park, partly because the nocturnal animals are difficult to spot. The estimate is a couple dozen.