Wolverine

Taxonomy

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

Within the Gulo gulo species, a clear separation occurs between 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 currently accepted taxonomy recognizes either the two continental subspecies or G. gulo as a single Holarctic taxon.

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 a stocky and muscular animal. With short legs, broad and rounded head, small eyes and short rounded ears, it more closely resembles a bear than it does other mustelids. Though its legs are short, its large, five-toed paws with crampon-like claws and plantigrade posture enable them 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 length usually ranging from 65–107 cm (26–42 in), a tail of 17–26 cm (6 ¹⁄₂–10 in), and a weight of 5.5–25 kg (12–55 lb), though exceptionally large males can weigh up to 32 kg (71 lb). Another outsized specimen was reported to scale approximately 35 kg (77 lb). The males are as much as 30% larger than the females and can be twice the females' weight. According to some sources, Eurasian wolverines are claimed to be larger and heavier than North American with average weights in excess of 20 kg (44 lb) but this may refer more specifically to areas such as Siberia, as data from European wolverines shows they are typically around the same size as their American counterparts. The average weight of female wolverines from a study in the Northwest territories of Canada was 10.1 kg (22 lb 4 oz) and that of males 15.3 kg (33 lb 12 oz). In a study from Alaska, the median weight of ten males was 16.7 kg (36 lb 13 oz) while the average of two females was 9.6 kg (21 lb 3 oz). In Ontario, the mean weight of males and females was 13.6 kg (30 lb 0 oz) and 9.9 kg (21 lb 13 oz). The average weights of wolverines were notably lower in a study from the Yukon, averaging 7.3 kg (16 lb 1 oz) in females and 11.3 kg (24 lb 15 oz) in males, perhaps because these animals from a "harvest population" had low fat deposits. In Finland, the average weight was claimed as 11 to 12.6 kg (24 lb 4 oz to 27 lb 12 oz). The average weight of male and female wolverines from Norway was listed as 14.6 kg (32 lb 3 oz) and 10 kg (22 lb). Shoulder height is reported from 30 to 45 cm (12 to 18 in). 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." 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.

Diet and hunting

Wolverines are considered to be primarily scavengers. A majority of the wolverine's sustenance is derived from carrion, on which it depends almost exclusively in winter and early spring. Wolverines may find carrion themselves, feed on it after the predator (often, a pack of wolves) has finished, or simply take it from another predator. Wolverines are also known to follow wolf and lynx trails, purportedly with the intent of scavenging 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. Prey mainly consists of small to medium-sized mammals, but the wolverine has been recorded killing prey such as adult deer that are many times larger than itself. 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, and coyote and wolf pups. Wolverines have also been known to kill Canadian 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.

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 not as 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 frequently 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.

Natural enemies

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. Another predator (less frequent) 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. In another account, a wolverine was claimed to have killed an adult polar bear but this account may be dubious.

Mating and reproduction

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.

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. 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 U.S. Fish and Wildlife Service publication, as of 2014 "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 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; no further wolverines have been spotted in Michigan.

Most New World wolverines live in Canada and Alaska.

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 mi²), 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.

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. 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 >800-mile 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 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.

Name

The wolverine's questionable reputation as an insatiable glutton (reflected in the Latin genus name Gulo) may be in part due to a false etymology. The less common name for the animal in Norwegian, fjellfross, meaning "mountain cat", is thought to have worked its way into German as Vielfraß, which means "glutton" (literally "devours much"). Its name in other West Germanic languages is similar (e.g. Dutch: veelvraat).

The Finnish name is ahma, derived from ahmatti, which is translated as "glutton". Similarly, the Estonian name is ahm, with the equivalent meaning to the Finnish name. In Lithuanian is ernis, in Latvian—tinis or āmrija.

The Eastern Slavic росомаха (rosomakha) and the Polish and Czech name rosomák seem to be borrowed from the Finnish rasva-maha (fat belly). Similarly, the Hungarian name is rozsomák or torkosborz which means "gluttonous badger".

In French-speaking parts of Canada, the wolverine is referred to as carcajou, borrowed from the Innu-aimun or Montagnais kuàkuàtsheu. However, in France, the wolverine's name is glouton (glutton).

Purported gluttony is reflected neither in the English name wolverine nor in the names used in North Germanic languages. The English word wolverine (alteration of the earlier form, wolvering, of uncertain origin) probably implies "a little wolf". The name in Proto-Norse, erafaz and Old Norse, jarfr, lives on in the regular Icelandic name jarfi, regular Norwegian name jerv, regular Swedish name järv and regular Danish name jærv.