Four environmental groups filed suit in a federal district court Wednesday over the U.S. Fish and Wildlife Service’s refusal to consider the wolverine for the endangered species list.

The lawsuit, filed in Missoula, Mont., is the latest in a five-year effort to force the agency to take steps to protect the reclusive predator and its high-elevation habitats. The suit was filed in Montana because the state is one of the few remaining areas where the wolverine is known to exist. Trapping of wolverines is legal in the state.

"There are a lot of indications that things are not going well for the wolverine, but the Fish and Wildlife Service doesn’t want to open an investigation," said attorney Tim Preso of Earthjustice, a nonprofit law firm based in Oakland, Calif.

Preso represents the groups in the suit, including Ashland-based Klamath-Siskiyou Wildlands Center. Other plaintiffs are Defenders of Wildlife in Washington, D.C.; Friends of the Clearwater in Moscow, Idaho; and Northwest Ecosystem Alliance in Bellingham, Wash.

Wolverines weigh about 60 pounds in adulthood and resemble a weasel. They make their dens under snow cover in remote areas usually at altitudes of 6,000 to 7,000 feet, said Jeff von Kienast, a wildlife biologist with the Prospect Ranger District of the Rogue River-Siskiyou National Forest. They are known to exist in the northern Cascades of Washington, and the Rocky Mountains of Idaho, Montana and Wyoming.

The wildlife service rejected a petition from the groups in October 2003 to study how many wolverines survive and whether they are in danger of extinction.

The agency determined there was not enough information about the animal to warrant an investigation at the time, said Diane Katzenberger, spokeswoman at the service’s regional office in Denver.

"Wolverines naturally occur in low density, so they are difficult to observe," Katzenberger said. "A lack of sightings doesn’t mean the numbers are declining."

She said the agency would consider the animal for the endangered list if new information indicated there are serious threats to its existence.

The fear among environmental groups is that the wildlife service might not find out whether the wolverine is in peril until it is too late, said Joseph Vaile, spokesman for the Klamath-Siskiyou Wildlands Center in Ashland. 

Development, logging, snowmobiling and other extreme winter sports are believed to drive the animal out of its habitat, Vaile said.

"If it should be protected, we would like to know," he said.

Oregon listed the animals as a threatened species in 1973. There have been no confirmed sightings of them in Oregon since the 1990s, von Kienast said.

There are about two to five credible reports of wolverine sightings in southwest Oregon each year, though none have been confirmed, he said. 

The state started doing regular surveys with helicopters and baited camera stations in 1993 to locate wolverines in the Rogue River-Siskiyou National Forest.

"We’ve had a pretty intensive effort, and we’ve come up empty," von Kienast said.