CHEYENNE -- A petition to list black-footed ferret populations in three states as endangered is frivolous and the U.S. Fish and Wildlife Service should ignore it, a Wyoming Game and Fish Department official said Friday.

Ferret numbers have rebounded in southeastern Wyoming's Shirley Basin thanks in no small measure to cooperation from private landowners who have allowed the critters on their property. Now, those ranchers worry that an endangered species listing could restrict how they may use their land, said Bob Oakleaf, nongame species coordinator for the department.

He called on the U.S. Fish and Wildlife Service to reject the environmentalists' request.

"They've done the damage," Oakleaf said. "They've created a doubt with the landowners and created a worry and a concern, and it's a legitimate concern."

The groups WildEarth Guardians, Biodiversity Conservation Alliance and Center for Native Ecosystems filed the petition Tuesday to list black-footed ferret populations in Arizona, South Dakota and Wyoming as endangered. The three ferret populations are at risk because of widespread shooting and poisoning of prairie dogs, which are the ferrets' only prey, the petition says.

It's not a frivolous petition, said Lauren McCain, with WildEarth Guardians.

"This is one of the most critically imperiled species that we have in this country," McCain said.

Landowners have nothing to fear, she said, because the petition seeks endangered status only for ferrets on public land, not for ferrets on private land.

The current status of black-footed ferrets is a Catch-22. The species is listed as endangered nationwide except in 17 areas in eight states where black-footed ferrets have been reintroduced.

But those are the only areas where black-footed ferrets are known to exist in the wild. In other words, no wild ferrets -- only those in zoos and captive-breeding programs -- are listed as endangered.

Wild ferrets are designated "nonessential experimental" populations.

Oakleaf said the petition is "basically huff and puff." He pointed out that ferret numbers in the Shirley Basin have surged from about 50 animals in the mid-1990s to around 500 today.

No wide-scale poisoning of prairie dogs occurs in that area, he said. Some people shoot prairie dogs, he said, but that has no long-term effect on prairie dog numbers -- or ferret numbers.

"We have no indication that has bothered the ferrets at all. They've increased right in the middle of where they are shooting," he said.

McCain, however, said the Shirley Basin ferret population was unsuccessful for a long time. She said the ferrets remain vulnerable to plague, which can wipe out ferrets in large numbers.

"They don't have a long enough trend line to determine whether that population is going to be a long-term success or not," she said.

Sharon Rose, a Fish and Wildlife Service spokeswoman, said whether the petition is reviewed in depth will depend in part on the agency's budget and staffing.