Wolverine

Gulo gulo

Wolverines (Gulo gulo) are part of the weasel or Mustilidae family.  This family includes skunks, badgers, weasels and otters.  Mustilidaes are characterized by anal musk glands that secrete a tannish-yellow colored pungent odor.  The species Gulo gulo incorporates all wolverines and is separated into two sub-species: Gulo gulo gulo and Gulo gulo luscus.  Gulo gulo luscus inhabits northern portions of Europe and Asia.

The North American wolverine, Gulo gulo gulo, historically ranged throughout the arctic regions and boreal forests of Alaska and Canada, and south through the northern portion of the lower 48, stretching south along the Rocky Mountain and Cascade Mountain regions.  The states that historically supported wolverines within the contiguous United States were Arizona, California, Colorado, Idaho, Indiana, Iowa, Maine, Michigan, Minnesota, Montana, Nebraska, Nevada, New Hampshire, New Mexico, New York, North and South Dakota, Oregon, Ohio, Pennsylvania, Utah, Vermont, Washington, Wisconsin, and Wyoming.  Of these states, known healthy wolverine populations inhabit Idaho and Montana.  In the Cascade region of Washington and Oregon, wolverines have been sighted. 

In the Sierra Nevada mountain range, the wolverine population recently may have become locally extinct.  Canada and Alaska continue to support healthy and viable populations.

Within their current range, North American wolverines inhabit isolated alpine and subalpine ecosystems of montane roadless or wilderness areas containing a diverse prey base and limited exposure to human activity.  During the winter months, wolverines occupy lower elevations to avoid the snow.

North American wolverines are scavengers, eating mostly carrion, requiring them to have a highly developed sense of smell and occur in low densities.  They can smell carrion under 1-2 meters of snow and across long distances.  Their jaw and skull structure enable them to easily crush frozen carrion and large bones.  Wolverines also predate upon ground squirrels, snowshoe hare, mice, and voles, and forage for various berries.  Wolverines forage for carrion within designated home ranges.  Home range size depends upon size of intact landscape, diversity of prey base, and sex.  Males typically have larger home ranges than females.  Male home ranges in Alaska have been documented between 422 and 666 square kilometers and females between 94 and 388 square kilometers.  Due to their need for large tracts of land to roam and forage, wolverines require a landscape that is not fragmented.

North American wolverines mainly breed during the summer, but breeding during the spring and fall has been documented.  The fertilized eggs lay dormant until the winter when the embryo begins to develop in December or January.  Litters of 1-5 offspring are born between February and April.  Young leave the den at 12-14 weeks and reach adult weight by winter.  Females den in uprooted trees, burrows, caves, overhanging banks and snow tunnels.

Wolverine’s main predators are humans, who trap wolverines for their fur.  Trapping is limited to the states of Montana and Alaska, where viable populations still exist.  Their black to medium-brown fur is highly desirable because of its layers of underfur and guard hairs.  The dense underfur is 2-3 cm long, mixed with 6-10 cm long guard hairs.  The tail fur is 15-20 cm long.  In areas where wolverine trapping is prohibited, wolverines are susceptible to traps set for coyotes, bobcats, wolves, and lynx due to their scavenging behavior.  Transient juveniles who have not established a home range have higher trapping occurrences.  Trapping juveniles decreases potential viability of populations due to loss of potential breeding age wolverines.  Injuries, resulting from encounters with traps, decreases chance of survival.

Although trapping accounts for part of the drastic decline of wolverines, many human induced factors attribute to population declines and losses.  The greatest cause of decline is loss of habitat. Throughout wolverines’ historic range, habitat loss is attributed to development, mining, logging, and other destructive activities.  Most of the remaining habitat suffers from fragmentation, increasing the likelihood of curtailment of existing populations.  Road construction in potential or used habitat, which is mainly attributed to logging, increases trapping and hunting opportunities, and increases landscape fragmentation.

North American wolverines have been listed as a threatened species in Oregon by the Oregon Department of Fish and Wildlife since 1989. In December 2000, KS Wild and a coalition of groups, led by the Center for Biological Diversity, filed a lawsuit against the U.S. Fish and Wildlife Service for failing to list this wildlands-dependent forest carnivore. 

The wolverine historically occupied much of the continental 48, but has been extirpated due to trapping, roadbuilding, logging and habitat fragmentation. There are recent, reliable sightings scattered in very remote areas of the south Cascades and the Klamath-Siskiyous. Populations of this species occur in low densities and need huge tracts of wilderness to meet survival requirements.