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Wolverine Gulo gulo
ESA status: proposed for listing (North American subspecies Gulo gulo luscus, contiguous U.S. population)

Wolverine

The more we learn about wolverines, the more we find to admire. These elusive denizens of frozen mountain tops were celebrated by Native Americans as powerful, all-terrain, all-season masters of the icy North. Also called “mountain devil” and “carcajou” (French for “evil spirit”), wolverines, according to some, make the Tasmanian devil look like a sissy. Wolverines, perfectly adapted to (and strictly limited to) their high-elevation habitats, will travel miles and miles atop deep snow and rough terrain using their large crampon-clawed feet in search of food, mates, and a home. Wolverines are fierce: they can kill prey many times their size and will defend food against much larger competitors—even grizzly bears. While this ultimate survivalist is more than capable of providing for itself, it has no defense against climate change or traps. Global warming is reducing wolverine habitat and now threatens to extirpate the species in the United States south of the Canadian border. Trapping is an additional threat to their tiny population in Montana.

The wolverine, a member of the weasel family, resembles a small bear – but with a bushy tail. It has a thick, dark, oily, double coat of fur that protects the animal from extreme cold. Some individuals have a light silvery facial mask and pale buff stripes that run laterally from each shoulder down the sides and connecting at the rump just above the tail. The species has short, powerful legs, and all four feet have five toes with long, curved claws used for digging and climbing. Adult males weigh between 26-40 pounds; females are smaller, weighing between 17-26 pounds.

Wolverines need a lot of space to find enough food to meet their high caloric needs in their relatively unproductive habitat—the average home range for males in Idaho is 588 square miles. Wolverines are opportunistic feeders and will consume a variety of foods, depending on availability. They primarily scavenge on carrion—even crunching the bones of carcasses that grizzly bears leave behind—but also prey on small animals and birds, and eat fruits, berries and insects. Food scarcity is a primary limitation on reproduction. Females will not become pregnant until age 2 and commonly reabsorb or spontaneously abort litters when resources are limited. Females may only breed every other year so as to save energy resources needed for winter survival in extreme temperatures.

Wolverines are found throughout the Northern hemisphere. In North America, they live in boreal forests, tundra, and alpine habitats throughout Alaska and Canada. The southern portion of their range includes alpine regions in Washington, Oregon, California, Idaho, Montana, Wyoming, Colorado and Utah. Female wolverines require a stable snow pack late in the warm season for denning and successful reproduction. This means that in the southern portion of its range where ambient temperatures are warmer, wolverines are confined to only the coldest, highest elevations.

Climate change is a primary threat to wolverines. Increasing temperatures melt winter snow more quickly in spring, hindering denning and reproduction. The loss of snowpack further diminishes the small, patchy habitats remaining in the lower 48 states, and reduces connectivity between isolated populations. High elevation alpine forests are also expected to shrink and shift northward as the climate warms, further stressing wolverines. 

In Montana, wolverines are still trapped and killed for their fur, or are caught in traps intended for other species. Some wolverines captured as part of biological study projects lost toes or teeth struggling to escape leg-hold traps. Trapping can completely eliminate a local population of wolverines. In one instance, trappers killed two pregnant females and four adult males in a region which resulted in the loss of the entire subpopulation. Losses of individual wolverines to traps restrict gene flow and hinders population growth in the metapopulation.

Experts agree that wolverines must be restored to the Southern Rocky Mountains, particularly in Colorado, where at least some habitat will remain in an era of global warming. WildEarth Guardians supports well-planned wolverine restoration in the state that supports reproduction and connectivity between subpopulations, and addresses threats to the species, including growth, poisonous sodium cyanide M-44 traps, and other factors.

Only 250-300 wolverines are estimated to remain in the lower 48 states. Conservation organizations first petitioned to list the species as “threatened” or “endangered” in the contiguous United States in 1995. After years of legal wrangling, the U.S. Fish and Wildlife Service finally designated wolverines in the lower 48 states as a candidate for listing under the Endangered Species Act in 2010. While the listing is pending, WildEarth Guardians and partners petitioned and then sued the State of Montana for allowing wolverine trapping in the state.