Thirty-one black-footed ferrets were released into the wild in Colorado yesterday, 58 years after the animal was last sighted in the state. The release near Rangley, Colo., was the ninth on the continent since the U.S. began a captive-breeding program to save the species 14 years ago; the animals have also been set loose in Arizona, South Dakota, Utah, Wyoming, and Mexico. Officials hope to remove the animal from the endangered species list by 2010, but before then, they’ll have to boost the population in the wild to a total of 1,500, with at least 30 breeding adults at each of 10 locations. About 500 black-footed ferrets are now running free.