DENVER (AP) — Rare black-footed ferrets chattered angrily before dashing out of pet carriers and ducking into burrows Monday at the Rocky Mountain Arsenal National Wildlife Refuge — a milestone for the highly endangered animals and for the former toxic waste site on the industrial edge of Denver.

The U.S. Fish and Wildlife Service released 30 ferrets at the site, part of a program to reintroduce them in 12 states where they once thrived, from Montana to Texas.

"They're a native species. They belong here," said Kimberly Fraser, an outreach specialist with the reintroduction program.

Their new home is a 25-square-mile preserve of short-grass prairie in Commerce City, a northeast Denver suburb. Chemical weapons and pesticides were once manufactured there, but it became a wildlife refuge in 2010 after a $2.1 billion cleanup.

"This remarkable place shows that nature will recover and will thrive if given a chance," said Fish and Wildlife Service Director Dan Ashe, who watched some of the releases.

Black-footed ferrets were once thought to be extinct, but a small colony was discovered in 1981 in Wyoming. Researchers have been trying to restore the population since then.

The long, slender creatures have short legs, appealing faces and an appetite for prairie dogs, which make up 90 percent of their diet. Adult ferrets can be up to 24 inches long and weigh 2½ pounds.

"They have a lot of hair, big bad teeth and a bad-boy attitude," Fraser said.

Ferrets' historic range extended from southern Canada to northern Mexico and eastern Nebraska to western Arizona, but their numbers plummeted as prairie dogs were exterminated as pests or died from plague, and their habitat was reduced by development.

The Black-Footed Ferret Recovery Program breeds the animals in captivity at six sites then prepares them for release in outdoor pens where they can kill prairie dogs.

Officials estimate about 300 ferrets now live in the wild from Canada to Mexico. They have been reintroduced at 24 sites in Arizona, Colorado, Kansas, Montana, New Mexico, South Dakota, Utah and Wyoming, and in the Canadian province of Saskatchewan and the Mexican state of Chihuahua.

Survival rates range from zero to 75 percent, said Pete Gober, the program coordinator. The biggest factor is whether plague kills the prairie dogs the ferrets depend on, he said.

The goal of the recovery program is to build a population of 3,000 adults across that range, Gober said.

At the Rocky Mountain Arsenal refuge, the ferrets join a bison herd that was reintroduced in 2007. The refuge is also home to prairie dogs, deer, rabbits, coyotes, eagles, hawks, meadowlarks and other native prairie wildlife.

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Online:

Rocky Mountain Arsenal National Wildlife Refuge: http://www.fws.gov/refuge/Rocky_Mountain_Arsenal/

Black-Footed Ferret Recovery Program: http://blackfootedferret.org/

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