Wolverine

The wolverine is the largest land-dwelling member of the family Mustelidae, a muscular, solitary carnivore of remote northern boreal forests and subarctic and alpine tundra, with the greatest numbers in northern Canada, Alaska, the mainland Nordic countries and western Russia and Siberia. It is primarily a scavenger, eating mostly carrion, especially in winter and early spring, and often follows wolf and lynx trails to reach their leftovers. It is also a capable predator and has been recorded killing prey many times its own size, such as adult deer. Large paws with crampon-like claws let it climb steep cliffs, trees and snow-covered peaks.

About the wolverine

The wolverine is a stocky, muscular carnivore and the largest land-dwelling member of the weasel family, Mustelidae. Its closest relatives are the martens and the tayra. It lives in remote boreal forest, tundra and mountains across the far north of North America, Europe and Asia, and is famous for strength out of proportion to its size.

Its scientific name, Gulo gulo, comes from the Latin for "glutton," a reputation that may rest partly on a mistranslation of an old Norwegian name meaning "mountain cat." The English name probably means "little wolf," and it has also been called carcajou, quickhatch, "skunk bear" and "nasty cat," the last two for its powerful smell.

A wolverine is about the size of a medium dog, and in build it most closely resembles a large fisher. The body is long and low, with strong legs, a broad, rounded head, small eyes and short, round ears. Males are typically 10–15 percent longer than females and 30–40 percent heavier. Only a few otters and, at times, the European badger match or exceed it in size within the weasel family.

The coat is thick, dark and oily. It sheds water so well that it resists frost, which made it a traditional lining for Arctic parkas. A pale buff stripe runs along each side from the shoulder across the rump to the bushy tail, and many animals have a silvery facial mask or white patches on the throat or chest.

The feet are built for snow and rock. Large, five-toed paws with crampon-like claws, and a flat-footed walk, let the wolverine climb steep cliffs, trees and snowy peaks with ease. Inside the mouth, a special upper molar is rotated 90 degrees, which helps it tear meat from carcasses frozen solid.

Behavior and diet

Wolverines are solitary and mainly scavengers. Most of their food is carrion, especially in winter and early spring, and they often follow wolf and lynx trails to feed on leftovers, or take kills from other predators outright. Their hurried, wolfing style of eating is thought to be an adaptation to scarce winter food.

They are also powerful hunters. Most prey is small to medium-sized, including porcupines, squirrels, beavers, marmots, rabbits, voles and lemmings, but wolverines have killed animals many times their size, such as deer, caribou and even moose and elk weakened by winter or stuck in deep snow. They also kill smaller predators, including martens, foxes and Canada lynx, and have been seen killing golden eagles at the nest. Eggs, birds, roots, seeds, insect larvae and berries round out the diet. In times of plenty they cache food, which is vital for nursing females in late winter.

Wolverines in Fennoscandia hunt more actively than North American ones, possibly because there are fewer competing predators to scavenge from.

Despite their toughness, wolverines have enemies. Gray wolves are their most important predator, and wolverines appear to abandon an area when wolves arrive. Cougars, American black bears and brown bears also kill them, and golden eagles can take young ones.

Breeding is unusual. Wolverines mate in summer, but the embryo does not implant until early winter. Successful males pair for life with two or three females, visiting them occasionally. Pregnant females dig dens in deep snow in February. After a gestation period of 30–50 days, usually two or three kits are born in spring. Kits are weaned at about 10 weeks and reach adult size within their first year. Fathers visit their young, and some travel with them for a time once the kits are about six months old. Females often skip breeding when food is scarce.

Range and habitat

Wolverines live mainly in isolated arctic, boreal and alpine regions of northern Canada, Alaska, Siberia and Fennoscandia, and are also native to European Russia, the Russian Far East, northeast China and Mongolia. Two subspecies are generally recognized, the Old World Gulo gulo gulo and the New World G. g. luscus.

In the Lower 48 United States, the species once ranged as far as Colorado, Arizona, New Mexico, the Midwest, New England, New York and Pennsylvania. Today small populations survive in the North Cascades of Washington and the northern Rocky Mountains of Idaho, Montana, Oregon's Wallowa Range and Wyoming. Lone wanderers turn up elsewhere. In 2020 a female with two young was seen at Mount Rainier, the first sighting there in more than a century, and one young male tagged near Grand Teton National Park in 2009 traveled more than 1,300 km (800 mi), to Colorado and later North Dakota.

These are animals of big, empty country. Females use home ranges of about 130–260 km² (50–100 sq mi), and a male's range can top 620 km² (240 sq mi), overlapping several females. Because denning females need snow that lasts into spring, wolverines are largely restricted to areas with late snowmelt.

Conservation status

Worldwide, the wolverine is listed as Least Concern because of its wide distribution and large remaining populations. Its total population is unknown, and it lives at low densities. Numbers have steadily declined since the 19th century because of trapping, range loss and habitat fragmentation, and the species has largely vanished from the southern edge of its range in both Europe and North America.

In the United States, the U.S. Fish and Wildlife Service proposed protection under the Endangered Species Act in 2013, citing shrinking winter habitat in the northern Rockies. In November 2023 it listed wolverines in the Lower 48 states as threatened. Because dens depend on spring snow, global warming is a concern for the species' future range.

Colorado passed a law in 2024 authorizing reintroduction, with plans to release 15 wolverines a year for three years. It will be the first attempt to bring wolverines back to a region where they had been wiped out. Around a hundred wolverines live in captivity in North America and Europe, where breeding has proved difficult, with high infant mortality.