Wolverine

Taxonomy and evolutionary history

Classification

Genetic evidence suggests that the wolverine is most closely related to the tayra and martens, all of which shared a Eurasian ancestor.

There are two subspecies: the Old World form, Gulo gulo gulo, and the New World form, G. g. luscus. Some authors had described as many as four additional North American subspecies, including ones limited to Vancouver Island (G. g. vancouverensis) and the Kenai Peninsula in Alaska (G. g. katschemakensis). However, the most accepted taxonomy recognizes either the two continental subspecies or G. gulo as a single Holarctic taxon.

Evolution

Recently compiled genetic evidence suggests most of North America's wolverines are descended from a single source, likely originating from Beringia during the last glaciation and rapidly expanding thereafter, though considerable uncertainty to this conclusion is due to the difficulty of collecting samples in the extremely depleted southern extent of the range.

Physical characteristics

Anatomically, the wolverine is an elongated animal that is low to the ground. With strong limbs, broad and rounded head, small eyes and short rounded ears, it most closely resembles a large fisher. Though its legs are short, its large, five-toed paws with crampon-like claws and plantigrade posture enable it to climb up and over steep cliffs, trees and snow-covered peaks with relative ease.

The adult wolverine is about the size of a medium dog, with a body length ranging from 65–109 cm (26–43 in); standing 36–45 cm (14–18 in) at the shoulder; and a tail length of 17–26 cm (6+1⁄2–10 in). Weight is usually 11–18 kg (24–40 lb) in males, and in females 8–12 kg (18–26 lb). Exceptionally large males of as much as 32 kg (71 lb) are referenced in Soviet literature, though such weights are deemed in Mammals of the Soviet Union to be improbable. The males are often 10–15% larger than the females in linear measurements and can be 30–40% greater in weight. According to some sources, Eurasian wolverines are claimed to be larger and heavier than those in North America, with weights of up to 20 kg (44 lb). However, this may refer more specifically to areas such as Siberia, as data from Fennoscandian wolverines shows they are typically around the same size as their American counterparts. It is the largest of terrestrial mustelids; only the marine-dwelling sea otter, the giant otter of the Amazon basin and the semi-aquatic African clawless otter are larger—while the European badger may reach a similar body mass, especially in autumn.

Wolverines have thick, dark, oily fur which is highly hydrophobic, making it resistant to frost. This has led to its traditional popularity among hunters and trappers as a lining in jackets and parkas in Arctic conditions. A light-silvery facial mask is distinct in some individuals, and a pale buff stripe runs laterally from the shoulders along the side and crossing the rump just above a 25–35 cm (10–14 in) bushy tail. Some individuals display prominent white hair patches on their throats or chests.

Like many other mustelids, it has potent anal scent glands used for marking territory and sexual signaling. The pungent odor has given rise to the nicknames "skunk bear" and "nasty cat." The anal gland secretion for the samples obtained from six animal's secretion was complex and variable: 123 compounds were detected in total, with the number per animal ranging from 45 to 71 compounds. Only six compounds were common to all extracts: 3-methylbutanoic acid, 2-methylbutanoic acid, phenylacetic acid, alpha-tocopherol, cholesterol, and a compound tentatively identified as 2-methyldecanoic acid. The highly odoriferous thietanes and dithiolanes found in anal gland secretions of some members of the Mustelinae [ferrets, mink, stoats, and weasels (Mustela spp.) and zorillas (Ictonyx spp.)] were not observed. The composition of the wolverine's anal gland secretion is similar to that of two other members of the Mustelinae, the pine and beech marten (Martes spp.)

Wolverines, like other mustelids, possess a special upper molar in the back of the mouth that is rotated 90 degrees, towards the inside of the mouth. This special characteristic allows wolverines to tear off meat from prey or carrion that has been frozen solid.

Wolverines have the highest compressive strength per trabecular bone volumetric fraction (A 10mm high × 5mm diameter cylinder) at the mandibular condyle among all carnivore mammals at 940.8 Newtons, followed by the cheetah at 784.4 Newtons, the Malagasy civet at 714.4 Newtons, the honey badger at 710.8 Newtons and the kinkajou at 693.2 Newtons.

Distribution

Wolverines live primarily in isolated arctic, boreal, and alpine regions of northern Canada, Alaska, Siberia, and Fennoscandia; they are also native to European Russia, the Baltic countries, the Russian Far East, northeast China and Mongolia.

Wolverine remains have been found in Ukraine, but they were extirpated and it is unclear whether the wolverines would have formed sustainable populations.

The species was present in Scotland until 6,000 BC.

Unique records of encounters with wolverines have been noted in Latvia, the most recent one being in late July 2022 (although it can be disputed because of the unclear footage); the population was widespread in the 16th and 17th centuries, but it is no longer native to the area.

Most New World wolverines live in Canada and Alaska. However, wolverines were once recorded as also being present in Colorado, areas of the southwestern United States (Arizona and New Mexico); the Midwest (Indiana, Nebraska, North and South Dakota, Ohio, Minnesota, and Wisconsin); New England (Maine, New Hampshire, Vermont, and Massachusetts); and in New York and Pennsylvania.

In the Sierra Nevada, wolverines were sighted near Winnemucca Lake in spring 1995 and at Toe Jam Lake north of the Yosemite border in 1996; and later photographed by baited cameras, including in 2008 and 2009, near Lake Tahoe. According to a 2014 U.S. Fish and Wildlife Service publication, "wolverines are found in the North Cascades in Washington and the Northern Rocky Mountains in Idaho, Montana, Oregon (Wallowa Range), and Wyoming. Individual wolverines have also moved into historic range in the Sierra Nevada Mountains of California and the Southern Rocky Mountains of Colorado, but have not established breeding populations in these areas". In 2022, Colorado Parks and Wildlife considered plans to reintroduce the wolverine to the state.

Wolverines are also found in Utah but are very rarely seen, with only six confirmed sightings since the first confirmed sighting in 1979. Three of these six confirmed Utah sightings have been caught on video. A wolverine, a male, was finally captured and tagged in Utah in 2022 before being released back into the wild to better understand the animal's range.

In August 2020, the National Park Service reported that wolverines had been sighted at Mount Rainier, Washington, for the first time in more than a century. The sighting was of a reproductive female and her two offspring.

In 2004, the first confirmed sighting of a wolverine in Michigan since the early 19th century took place when a Michigan Department of Natural Resources wildlife biologist photographed a wolverine in Ubly, Michigan. The specimen was found dead at the Minden City State Game Area in Sanilac County, Michigan, in 2010.

Behavior and ecology

Diet and hunting

Wolverines are primarily scavengers. Most of their food is carrion, especially in winter and early spring. They may find carrion themselves, feed on it after the predator (often, a wolf pack) has finished, or simply take it from another predator. Wolverines are known to follow wolf and lynx trails to scavenge the remains of their kills. Whether eating live prey or carrion, the wolverine's feeding style appears voracious, leading to the nickname of "glutton" (also the basis of the scientific name). However, this feeding style is believed to be an adaptation to food scarcity, especially in winter.

The wolverine is also a powerful and versatile predator. Its prey mainly consists of small to medium-sized mammals, but wolverines have been recorded killing prey many times larger than themselves, such as adult deer. Prey species include porcupines, squirrels, chipmunks, beavers, marmots, moles, gophers, rabbits, voles, mice, rats, shrews, lemmings, caribou, roe deer, white-tailed deer, mule deer, sheep, goats, cattle, bison, moose, and elk. Smaller predators are occasionally preyed on, including martens, mink, foxes, Eurasian lynx, weasels, coyote, and wolf pups. Wolverines have also been known to kill Canada lynx in the Yukon of Canada. Wolverines often pursue live prey that are relatively easy to obtain, including animals caught in traps, newborn mammals, and deer (including adult moose and elk) when they are weakened by winter or immobilized by heavy snow. Their diets are sometimes supplemented by birds' eggs, birds (especially geese), roots, seeds, insect larvae, and berries. Adult wolverines appear to be one of the few mammalian carnivores to pose an active threat to golden eagles. Wolverines were observed to prey on nestling golden eagles in Denali National Park. During incubation in Northern Sweden, an incubating adult golden eagle was killed in its nest by a wolverine.

Wolverines inhabiting the Old World (specifically, Fennoscandia) hunt more actively than their North American relatives. This may be because competing predator populations in Eurasia are less dense, making it more practical for the wolverine to hunt for itself than to wait for another animal to make a kill and then try to snatch it. They often feed on carrion left by wolves, so changes in wolf populations may affect the population of wolverines. They are also known on occasion to eat plant material.

Wolverines often cache their food during times of plenty. This is of particular importance to lactating females in the winter and early spring, a time when food is scarce.

Reproduction

Wolverines are induced ovulators. Successful males will form lifetime relationships with two or three females, which they will visit occasionally, while other males are left without a mate. Mating season is in the summer, but the actual implantation of the embryo (blastocyst) in the uterus is stayed until early winter, delaying the development of the fetus. Females will often not produce young if food is scarce. The gestation period is 30–50 days, and litters of typically two or three young ("kits") are born in the spring. Kits develop rapidly, reaching adult size within the first year. The typical longevity of a wolverine in captivity is around 15 to 17 years, but in the wild the average lifespan is more likely between 8 and 10 years. Fathers make visits to their offspring until they are weaned at 10 weeks of age; also, once the young are about six months old, some reconnect with their fathers and travel together for a time.

Interspecies interactions

Wolves, American black bears, brown bears and cougars are capable of killing adult wolverines, while smaller predators (like golden eagles) can kill young and inexperienced individuals. Wolves are thought to be the wolverine's most important natural predator, with the arrival of wolves to a wolverine's territory presumably leading the latter to abandon the area. Armed with powerful jaws, sharp claws, and a thick hide, wolverines, like most mustelids, are remarkably strong for their size. They may defend against larger or more numerous predators such as wolves or bears. By far, their most serious predator is the grey wolf, with an extensive record of wolverine fatalities attributed to wolves in both North America and Eurasia. It has been reported that packs of grey wolves occasionally kill wolverines, either to defend their kills or to protect dens containing their own pups. In North America, another (less frequent) predator is the cougar. At least one account reported a wolverine's apparent attempt to steal a kill from a black bear, although the bear won what was ultimately a fatal contest for the wolverine. There are a few accounts of brown bears killing and consuming wolverines as well and, although also reported at times to be chased off prey, in some areas such as Denali National Park, wolverines seemed to try to actively avoid encounters with grizzly bears as they have been reported in areas where wolves start hunting them.

Urine scent marking

Wolverines have been observed to use urine as a scent-marking behavior. Headspace analysis of the volatiles emanating from urine samples identified 19 potential semiochemicals. The major classes of identified chemicals are the ketones: 2-heptanone, 4-heptanone and 4-nonanone and the monoterpenes: alpha-pinene, beta-pinene, limonene, linalool and geraniol. In other mammals, the excretion of these terpenes is unusual. The conifer needles that are found in wolverine scat are likely the source of these monoterpenes.

Threats and conservation

The world's total wolverine population is not known. The animal exhibits a low population density and requires a very large home range. The wolverine is listed by the IUCN as Least Concern because of its "wide distribution, remaining large populations, and the unlikelihood that it is in decline at a rate fast enough to trigger even Near Threatened".

The range of a male wolverine can be more than 620 km² (240 sq mi), encompassing the ranges of several females which have smaller home ranges of roughly 130–260 km² (50–100 mi²). Adult wolverines try for the most part to keep nonoverlapping ranges with adults of the same sex. Radio tracking suggests an animal can range hundreds of miles in a few months.

Female wolverines burrow into snow in February to create a den, which is used until weaning in mid-May. Areas inhabited nonseasonally by wolverines are thus restricted to zones with late-spring snowmelts. This fact has led to concern that global warming will shrink the ranges of wolverine populations.

This requirement for large territories brings wolverines into conflict with human development, and hunting and trapping further reduce their numbers, causing them to disappear from large parts of their former range; attempts to have them declared an endangered species have met with little success. In February 2013, the United States Fish and Wildlife Service proposed giving Endangered Species Act protections to the wolverine due to its winter habitat in the northern Rockies diminishing. This was as a result of a lawsuit brought by the Center for Biological Diversity and Defenders of Wildlife. In November 2023, the United States Fish and Wildlife Service announced that it was adding the wolverine in the United States Lower 48 states to the threatened list.

The Wildlife Conservation Society reported in June 2009 that a wolverine researchers had been tracking for almost three months had crossed into northern Colorado. Society officials had tagged the young male wolverine in Wyoming near Grand Teton National Park, and it had traveled southward for about 500 miles (800 km). It was the first wolverine seen in Colorado since 1919, and its appearance was also confirmed by the Colorado Division of Wildlife. In May 2016 the same wolverine was killed by a cattle ranch-hand in North Dakota, ending a greater-than-800-mile (1,300 km) trip by this lone male wolverine, dubbed M-56. This was the first verified sighting of a wolverine in North Dakota in 150 years. In February 2014, a wolverine was seen in Utah, the first confirmed sighting in that state in 30 years.

In 2024, Colorado's state government passed a bill authorizing the reintroduction of wolverines into the state. As of February 2026, Colorado Parks and Wildlife plans to release 15 wolverines annually over the course of three years. This will be the first attempt to reintroduce wolverines to a region where they have been extirpated.

In captivity

Around a hundred wolverines are held in zoos across North America and Europe, and they have been bred in captivity, but only with difficulty and high infant mortality.

Human interactions

Many North American cities, sports teams, and organizations use the wolverine as a mascot. For example, the US state of Michigan is, by tradition, known as "the Wolverine State", and the University of Michigan takes the animal as its mascot. There have also been professional baseball and football clubs called the "Wolverines". The association is well and long established: for example, many Detroiters volunteered to fight during the American Civil War and George Armstrong Custer, who led the Michigan Brigade, called them the "Wolverines". The origins of this association are obscure; it may derive from a busy trade in wolverine furs in Sault Ste. Marie in the 18th century or may recall a disparagement intended to compare early settlers in Michigan with the vicious mammal. Wolverines are, however, extremely rare in Michigan. A sighting in February 2004 near Ubly was the first confirmed sighting in Michigan in 200 years. The animal was found dead in 2010.

The Marvel Comics superhero James "Logan" Howlett was given the nickname "Wolverine" while cage fighting because of his skill, short stature, keen animal senses, ferocity, and most notably, claws that retract from both sets of knuckles.

The wolverine is prevalent in stories and oral history from various Algonquian tribes and figures prominently in the mythology of the Innu people of eastern Quebec and Labrador. The wolverine is known as Kuekuatsheu, a conniving trickster who created the world. The story of the formation of the Innu world begins long ago when Kuekuatsheu built a big boat similar to Noah's Ark and put all the various animal species in it. There was a great deal of rain, and the land was flooded. Kuekuatsheu told a mink to dive into the water to retrieve some mud and rocks which he mixed together to create an island, which is the world that is presently inhabited along with all the animals. Many tales of Kuekuatsheu are often humorous and irreverent and include crude references to bodily functions. Some Northeastern tribes, such as the Miꞌkmaq and Passamaquoddy, refer to the wolverine as Lox, who usually appears in tales as a trickster and thief (although generally more dangerous than its Innu counterpart) and is often depicted as a companion to the wolf. Similarly, the Dené, a group of the Athabaskan-speaking natives of northwestern Canada, have many stories of the wolverine as a trickster and cultural transformer much like the coyote in the Navajo tradition or raven in Northwest Coast traditions.