The black-footed ferret, North America's rarest mammal, is returning to the western prairie 35 years after being declared extinct.

The comeback trail for Mustela nigripes began in 1981, when a ranch dog with a dead ferret in its mouth led to the rediscovery of a remnant population near Meeteetse in northwestern Wyoming. (See stunning pictures of the rarest animals on Earth.)

The last 18 survivors of that population formed the seed stock for a captive-breeding program that reintroduced the species to its former range at 25 sites from southernmost Canada to northern Mexico. Yet numbers in the wild remain low—fewer than 500, according to Peter Gober, recovery coordinator at the U.S. Fish and Wildlife Service's National Black-Footed Ferret Conservation