FORT COLLINS — Chattering captive-bred endangered black-footed ferrets crept out of cages into public open space Wednesday — the first freed under a new Colorado law that lets cities and counties release ferrets into colonies of their prairie dog prey.

If these 15 ferrets hunt as they did in the federal government’s nearby breeding center, they each will eat at least a prairie dog a week and help restore ecological balance in an unusually large open space area covering 48,500 acres.

“It is the natural habitat where they started,” Fort Collins Mayor Karen Weitkunat said. “Because of the population of prairie dogs, we believe they will succeed.”

Other cities including Boulder have expressed interest in the possibility of reintroducing black-footed ferrets, formerly America’s most endangered mammals, as natural predators on open space.

But cities and counties must have at least 1,500 acres of un-fragmented land to be eligible, said Pete Gober, black-footed ferret recovery coordinator for the U.S. Fish and Wildlife Service.

“Ferret recovery is a pretty simple process. You put ferrets with prairie dogs. You manage to keep disease off the landscape. And you deal with boundary control so that you don’t have prairie dogs wandering off and becoming a nuisance,” Gober said. “If you’re committed to that kind of management, we will work with anyone to put ferrets out and have success.”

A law signed by Gov. John Hickenlooper in May lets cities and counties deploy black-footed ferrets, which in the mid-1980s were deemed extinct, under special agreements with federal wildlife authorities.

City and county officials must agree to prevent deliberate killing or harassing of ferrets. In return, federal officials agree not to impose regulatory restrictions and not consider “incidental killing” of ferrets as grounds for prosecution.

Next year, federal officials plan to reintroduce ferrets at the Rocky Mountain Arsenal National Wildlife Refuge north of Denver.

Ferrets historically hunted on Colorado grasslands. Poisoning and hunting rendered them scarce by the 1930s and nearly extinct by the 1980s. A small population was found in Wyoming. Federal biologists took those last 18 animals and bred them at the National Black-footed Ferret Conservation Center northeast of Fort Collins, where, with help from zoos, there are currently about 500.

USFWS regional director Noreen Walsh hailed the release on Fort Collins’ Soapstone Prairie Natural Area and adjacent Meadow Springs Ranch open space as a major step toward recovering black-footed ferrets as a self-sustaining population in the wild.

Federal officials aim to reintroduce 3,000 across 12 states. Colorado officials said 150 will be released here.

Ferrets typically weigh about 2 pounds; often they are smaller than their prey.

At night, ferrets’ elongated bodies and sensitive snouts let them slink into tunnels to underground dens where prairie dogs sleep. Ferrets clamp their teeth into prairie dogs’ necks and squeeze, then devour them. One female ferret typically will guard turf of about 100 acres.

Combatting plague that threatens prairie dogs and ferrets looms as a challenge. Colorado Parks and Wildlife officials are testing an anti-plague vaccine at the Soapstone area, luring prairie dogs to peanut butter-covered cubes containing the vaccine.

“We know that being able to manage plague is key to our success in recovering black-footed ferrets,” CPW assistant director Chad Bishop said.

Bruce Finley: 303-954-1700, bfinley@denverpost.com