WASHINGTON — The National Zoo's conservation center in Virginia is sending a group of black-footed ferrets to "boot camp" in Colorado to prepare the critters for life in the wild.

This shipment Wednesday is the latest step in an ongoing effort to restore the wild population of a species once declared extinct. Researchers rediscovered them in 1981 and collected the last 24 in Wyoming to try to save them. Now 1,000 are again living in the wild.

Black-footed ferrets are the only ferret native to North America. At least a half million used to live on the Great Plains. Prairie dogs are their main food source. But development, disease and extermination of prairie dogs starved them.

Boot camp gives them a chance to hunt prairie dogs before they're released.