LEWISTON – Several environmental groups filed a lawsuit Monday against the U.S. Fish and Wildlife Service, challenging the agency’s decision in October to deny Endangered Species Act protection for wolverines.

The groups say the small but feisty mammal is under threat of extinction in the lower 48 states because of climate change, habitat fragmentation and dwindling genetic diversity.

“I and countless other Idahoans were heartbroken when Idaho’s last remaining mountain caribou herd went extinct,” Brad Smith of the Idaho Conservation League said. “The Fish and Wildlife Service must act soon to ensure that Idaho’s wolverines do not share the same fate.”

The environmental law firm EarthJustice is representing the Center for Biological Diversity, Conservation Northwest, Defenders of Wildlife, Friends of the Clearwater, Idaho Conservation League, Jackson Hole Conservation Alliance, Klamath-Siskiyou Wildlands Center, Greater Yellowstone Coalition, Sierra Club and Rocky Mountain Wild in the litigation.

In declining to list the animal as a threatened species, the Fish and Wildlife Service said recent research indicated wolverine populations to be stable. The agency had proposed listing wolverines as a threatened species in 2013.

Conservation groups have been pushing for wolverine protections for about two decades. There are estimated to be about 250 to 300 wolverines spread across the high mountain ranges of Rocky Mountain and Pacific Northwest states. The reclusive animals are known for their tenacious and ferocious demeanors, but are also believed to require deep snow that persists well into spring to successfully reproduce.

“The U.S. Fish and Wildlife Service received a petition to protect the wolverine under the Endangered Species Act in 2000. Over these past 20 years, citizens and organizations have had to sue the agency five times over the wolverine, twice for utter inaction in making any decision and three times for failing to properly consider science when denying ESA protection,” Katie Bilodeau of Friends of the Clearwater said. “In each lawsuit, either the court found the agency’s decision unlawful or the agency chose not to defend its decision.”

The agency issued a statement defending its decision.

“New research and analysis show that wolverine populations in the American Northwest remain stable, and individuals are moving across the Canadian border in both directions and returning to former territories,” the statement said. “The species, therefore, does not meet the definition of threatened or endangered under the Endangered Species Act.”

Wolverines are the largest member of the weasel family, weighing 20 to 40 pounds. They are 3 to 4 feet long, with short legs, bushy tails, and appear to some people like small bears. Between February and May, females den and raise kits in the snowfields that cling to mountain peaks. Scientists have documented those sites are disappearing as the climate warms and spring snow melt accelerates. But federal officials said some research has documented wolverines denning in areas without persistent snow cover.

Their range includes the mountains of Washington, Idaho, northeastern Oregon, Montana, Wyoming and Colorado. Without federal protections, the animals will continue to fall under the management of state wildlife agencies.