The wolverine (Gulo gulo), sometimes called carcajou or skunkbear, is the largest land-dwelling mustelid (a family that includes weasels, badgers and otters) in the world. It is a circumpolar species, meaning that its range extends throughout the northern part of the northern hemisphere, where it prefers snowy habitats. In the 48 contiguous states, this includes the basins of high mountains, such as Utah’s Uinta Mountains.
Physical characteristics. Wolverines typically weigh between 20 and 50 pounds, with males being about half again as large as females. They have thick dark brown fur with a lighter whitish or tan stripe running across the shoulders and down the sides to the bushy tail. They have broad flattish heads with small rounded ears, small dark eyes and short legs with long claws for gripping ice. In appearance, they somewhat resemble bears.
Reproduction. Males will form lifetime relationships with up to three females, which they will visit occasionally. They mate in summer, but embryo implantation is delayed until early winter. The gestation period is approximately 50 days and typically produces two or 3 babies (“kits”). However, if food is scarce, females will not produce young. Wolverine young live protected inside a snow-covered rocky den, often at the base of a talus slope in high alpine basins. The kits are weaned at about 10 weeks and may live up to 17 years of age, but 8-10 is more common in the wild.
Diet. Wolverines are scavengers as well as hunters and rely to a great extent on carrion—dead animals that have died of starvation or disease or accident, or were killed by another animal, e.g., deer killed by a cougar. Wolverines are very aggressive and have been known to drive cougars and bears off of kills and usurping the kills. Mountain sheep and mountain goats occasionally fall of cliffs at the head of mountain basins and die. In winter the carcasses are preserved in snow and wolverines take advantage of this handy food supply. Thanks to a pair of rear molars that are turned inward 90 degrees, wolverines are able to tear chunks of frozen meat off carcasses. It is probably one reason why wolverine dens are often at the base of talus slopes high up in alpine basins, where animal carcasses can be preserved in deep snow for long periods. Wolverines will hunt and kill other animals for food, as well, and have been known to take marmots, hares, grouse, and even deer—occasionally even lynx. Its name is Latin for ‘glutton’ due to its reputation as having a voracious appetite. Wolves and mountain lions and golden eagles are known to prey on wolverines.
Home range and distribution. Because of the nutritional requirements of wolverines, the nature of their habitats and the general scarcity of food, they typically have large home ranges, ranging anywhere from 60 square miles to 1000 square miles or more, with male home ranges being much larger than female home ranges. For comparison, the High Uinta Wilderness is 714 square miles. When dispersing, young independent wolverines may travel hundreds of miles as they explore for a place to live and to find a mate. A juvenile male wolverine (M56) was trapped and collared in Grand Teton National Park in 2008 and subsequently traveled down the Wind River Range and across the Red Desert of southern Wyoming into Colorado. He stayed in Colorado for about three years, then disappeared. In 2016 he was shot by a rancher in North Dakota. While Utah is toward the southern extent of their range and doesn’t have a lot of prime wolverine habitat, the Bear River Mountains, Wasatch Mountains, and Uinta Mountains of northern Utah contain good wolverine habitat—enough to at least support dispersing wolverines as they travel between the southern Rockies of Colorado and the northern Rockies of Wyoming and beyond. One of the few literate trappers of his era, Osborne Russell, in his book Journal of a Trapper, recounts a disconcerting incident with a wolverine that “stole” a mountain sheep he had shot in the mountains near the mouth of Weber Canyon in February of 1841. That was prior to pioneer settlement. What was believed to be the last wolverine in Utah was shot near Dinosaur National Monument 138 years later in 1979. However, in 2014 a wolverine was photographed at a bait station high on Elizabeth Ridge on the north slope of the Uinta Mountains in 2014. (Elizabeth Ridge divides the Green-Colorado River watershed from the Bear River watershed.) It must have come from the north, since there are currently no known resident wolverines in Utah or Colorado. In July of 2016, another wolverine, a young female, was found dead on the side of a road at the eastern foot of the Bear River Mountains. These incidents are clear proof of the importance of the Bear River Mountain-Uinta Mountain linkage for wolverine conservation in the Rocky Mountains.
Conservation. There are estimated to be only about 100 wolverines in the contiguous 48 states, yet in recent years the population seems to have been expanding into parts of its range where it had been extirpated by traps and poisons decades ago. In addition to the examples cited above, recently wolverines have been documented in the Lake Tahoe area and on Mount Rainier. Because of this, as of October 8, 2020, the U.S. Fish and Wildlife Service has determined that the wolverine population in the 48 contiguous states is stable and has withdrawn its previous threatened species listing proposal. Despite this, wolverine recovery and conservation in the United States outside Alaska face multiple threats: climate change, habitat fragmentation, decline in bighorn sheep abundance, and trapping.