Wolverine

Page last updated: 29/11/2023

(Gulo gulo)

Photo by Adam Hammond (San Francisco Zoo).
Alternate coat with silvery mask and patches: Link

The wolverine, also referred to as the carcajou, quickhatch, misleadingly a “glutton”, and many other names, is the largest land-dwelling mustelid found throughout the far Northern Hemisphere.

There is a common impression that the wolverine’s bulky physique makes them the largest mustelid overall. However, this title (depending on which metric one prefers) can belong to either the giant otter (the longest) or the sea otter (the heaviest).

The wolverine is one of the most commonly misidentified animals on social media platforms. They tend to be confused with a wolf, bear, ratel, fisher, bobcat, lynx, species of badger, or even a hoary marmot, as well as many others.

Appearance

A mustelid with a robust yet athletic build, relatively short neck, powerful shoulders, and stocky body to help them preserve heat in cold climates. Their relatively long legs end in large paws that function as snowshoes, and each paw sports five thick crampon-like claws. The tail is short and bushy.

They have highly hydrophobic fur that is a thick, glossy, brown to brownish-black, with a yellow or gold stripe extending from the crown of the head laterally across each shoulder and to the rump, where the stripes join at the tail. A light silvery facial mask and white hair patch on the throat and or chest is distinct in some individuals.(1)

Habitat

The wolverine is found in the arctic and boreal forests, tundras, and mountainous regions of the Northern Hemisphere. They rely on cold climates that stay snowy well into spring, and rarely occur where the average maximum daily temperature in August is above 22°C (71.6°F).

Dens are made in the cavities of rocky terrain and under fallen trees buried by deep snow. Dens consist of feeding, nesting, and latrine chambers connected by a network of snow tunnels up to 60 metres (196.85 feet) long, often with multiple exits and entrances. The floor is often lined with bark mulch as the mother gnaws on the fallen tree during the construction of her den, though it is currently unclear whether this lining is intended as a bedding material or is simply a byproduct of the construction process.

Dens may be dug anywhere from one to five metres (three to sixteen feet) deep under the snow. The insulation provided by this snow cover is essential to keeping tiny kits warm as the mother is out hunting and scavenging. Due to this species’ obligate relationship with deep snow and cold it has been considered a sort of inland analogue to the polar bear when considering the impact of climatic changes.

Females establish multiple den sites and will often move kits around, especially if the den is disturbed.(2)(3)

Behaviour

“Although the fact seems to have been carefully overlooked, the hair-raising mythology of the wolverine goes back straight as a gun barrel to the brave old days when the buckskin pioneers, for amusement, convinced a lot of tenderfeet that mountain rams made a practice of jumping off cliffs and landing safely on their horns, that grizzly bears hugged human victims to death, that hoop snakes rolled eerily about among the sunburnt hills of the West, and that porcupines threw their quills out with the accuracy of Sioux arrows.

Our fun-loving trail-blazing forebears decided the wolverine was a sinister and malevolent little brute, a sort of wildlife outlaw, and consequently set about glamourizing him. When they went their way, they left today’s sportsmen and nature writers such a legacy of wild and wonderful legend about the animal that it is small wonder the wolverine of fact and the wolverine of storybooks have only a vague resemblance.” – Annabel, R. 1950. The myth of the Injun devil. Sports Afield. 123:42-43, 139-145.

It is impossible to ignore this animal’s reputation. The wolverine of legend bears little resemblance to the real animal, but this is not to say the real wolverine is any less impressive than its mythological counterpart. Wolverines are creatures of incredible vitality, courage, and tenacity, and live their lives with an enviable intensity; this much is true. An average, unremarkable gulo is capable of mountain ascents that the most successful human mountaineer would not dare try. They may confront a much larger predator with all the calculating confidence and guile of an experienced zookeeper. There is exhilarating footage of wolverines bringing down caribou in frontal assaults.(4) But the similarities to the legend end there.

They are more sociable than previously thought

The view of wolverines as bad-tempered, antisocial killing machines that only take a break from their relentless aggression to mate is inaccurate. In reality they are among the most social of mustelids. Adult males and females form lasting relationships and often travel together outside of the breeding season. Parents do not evict their kits as soon as they are capable of surviving on their own, as previously believed, but travel with them and allow them to continue using their territory until the kits establish their own. The wolverine is one of few mustelid species to exhibit paternal care. There is an account of an adult male wolverine sharing a meal with an unrelated subadult male. There is an account of a wolverine spending days at the side of his sibling’s corpse—possibly a sign of mourning—and there is even an account of a mother apparently burying her deceased kit.(3)(5)(6)

Their sociality becomes much more apparent in captivity when food scarcity is eliminated. Captive wolverines have distinct personalities and will form social groups, apparently often having “best friends” that are preferred playmates and companions. Disputes with other captives are usually settled with growls, bared fangs, flailing paws, and no bloodshed. Both captive and wild wolverines, kit and adult alike, are fond of play (though reportedly they become grumpy and aloof in old age). There is no shortage of accounts of wolverines play-wrestling, “dancing”, and even tumbling and sliding down snow banks and ice patches in the same fashion observed in otters.(3)(7) Hand-reared wolverines are notably loyal and affectionate toward their human handlers, even as adults.(8)

This is not to imply that wolverines are perfectly placid creatures that would make for a suitable family pet. Encounters between wild wolverines of the same sex often end violently. A trapped or cornered wolverine is, naturally, a force to be reckoned with. It would be inadvisable to stick one’s hand or head into a mother’s den. Wolverines are, after all, wild animals, and wild animals have strict boundaries and will react aggressively when threatened. But their aggressive nature is overstated, often to an absurd degree.

Overblown myths of aggression

Despite sensationalist rumours in popular media, fantasies of courage from those who likely provoke wildlife, and other regurgitated tales of danger, there exists not one single verifiable account of a wolverine attacking a human, let alone fatally.(9)(10)(11) Even if an account was documented it is clear such an attack would be extremely rare.

Wolverine researchers—whose field studies may involve live-trapping wolverines or digging into a den with the mother present to implant trackers in the kits—have never reported being attacked. Furious growling is common and the occasional bluff charge has been reported, but the wolverine invariably flees to a safe distance as soon as it is able (though it may immediately return to a trap for the bait or continue watching the researchers from a distance). All evidence suggests that wolverines avoid humans as much as possible and will only chance an encounter if the risk of starvation outweighs the risks of a nighttime raid of a camp’s meat supply or an improperly secured trash can. It is worth noting that reports of cabin break-ins and pilferages seem to only ever involve unoccupied cabins.

Understanding the wolverine’s aversion to confronting humans is useful for understanding reports of them driving wolves, mountain lions, and even bears from their kills. This kleptoparasitism is likewise motivated by hunger, not aggression. It is uncommon that the wolverine actually attacks its competitor beyond a simple bluff charge (a behaviour found throughout the animal kingdom), and these attacks are mostly quick hit-and-run nips or paw swipes intended to intimidate, not wound or kill. Wolverines are intelligent, calculating creatures and understand that an actual physical fight with these larger predators will go poorly. Indeed, there is no shortage of cases where a gulo’s miscalculation here has ended in its demise; far more than any alleged cases of one successfully killing its competitor.

It is likely the perception of wolverines and other mustelids as “ferocious” stems largely from their behaviour when caught in a trap. It is true these creatures will go into an apparent rage when trapped, but why expect an animal to behave differently when facing impending death? Wolverines have long been the object of much frustration for trappers of many cultures due to their raiding of traplines and reported difficulty of being captured. They have also invoked ire for their habit of fouling meat and occasionally breaking into and ransacking cabins, sometimes marking and/or releasing musk inside. All of these behaviours are adaptations for survival, not something a wolverine does out of “spite”.

Wolverines live in some of the most inhospitable environments on earth. Being mustelids they have very active metabolisms and little in the way of fat reserves, and thus are constantly at risk for starvation. A trapped animal makes for an easy meal, irresistible particularly during a time of year when food is scarce. A wolverine may urinate on surplus meat to dissuade other carnivores from eating it; this meat is still perfectly edible for the wolverine. A cabin full of supplies is obviously something a resourceful animal would lay claim to. The release of musk is incidental; musking is an involuntary response to fear in wolverines and not done for marking.(3)

Maintaining territory

Wolverines have massive home ranges, likely due in part to the low density of food available in their range during winter. Range size varies greatly depending on factors such as topography and quantity of suitable den sites, with reported figures varying from 422 to 1,506 square kilometres (163 to 581 square miles) for males and 73 to 335 square kilometres (28 to 129 square miles) for females. Territory is marked with scent, primarily through urine and scat deposits and with glands on the abdomen and paws. Wolverines patrol their territory tirelessly not only in search of food but to maintain these scent markers and discourage intruders.(2)

Maintaining a range of this size has resulted in wolverines developing tremendous physical endurance. One would be hard pressed to find an animal as adept at traversing snowy and mountainous terrain as Gulo gulo. The mid-2000’s Glacier National Park Wolverine Project found the average adult male wolverine to travel about 150 kilometres (93 miles) per week; as the name would imply, Glacier National Park is not a particularly flat landscape. Much of this travel occurred along the top of mountain ridges, and were occasionally punctuated by the submitting of prominent peaks. During this study an adult male identified as “M3” summited 1,593 metre (1 mile) Mount Cleveland in under 90 minutes.(5) An adult female, “F5”, summited 330 metre (0.2 mile) Bearhat Mountain (which appears in photos to be almost comically insurmountable) in April, when the mountain was encased in snow and ice.(3)

Young wolverines of both sexes may disperse long distances, sometimes hundreds of kilometres, when seeking their own territory.(2)(5) As wolverines have rather particular habitat requirements (and this habitat is progressively shrinking) no desirable territory goes uncontested for long. An established, resident adult must constantly remain vigilant for intruders. It is an unfortunate reality of the wolverine world that even the most suitable habitat cannot support a very dense wolverine population. Any intruder that can establish itself in a resident’s territory is a competitor for mates and for the scarce food available for the resident, its mate(s), and its kits. When one pairs this reality with the observation that properly-husbanded captive wolverines are generally quite tolerant of unrelated conspecifics it becomes evident that the infamous wolverine “aggression” stems from scarcity, not an innate hostility.

Reproduction

Breeding season for Gulo gulo is May to August, with most pairings happening June-July. Wolverines have a polygynous mating system; a dominant, resident male will mate with multiple females within his territory while other males do not breed. Courtship and mating behaviours are currently unknown.(2)

Like many mustelids, wolverines exhibit delayed implantation. Implantation usually occurs December-February. Gestation lasts 30 to 50 days. Parturition occurs January to April, usually February-March. Litter size is one to five, usually two to three.(5)(12) Newborn kits are altricial, usually weigh less than 100 grams (3.5 ounces), have pure white fur, and, according to one source, have a foul-smelling, waxy substance on their necks.(3) The sex ratio is around 50:50.(5)

Young are weaned and begin travelling with their mothers at 9-10 weeks old. They become nutritionally independent around six to seven months old but often continue travelling with their parents—now including the father—until they disperse to seek their own territory. Sexual maturity is reached around 15 months for females, two years for males. Females usually do not reproduce until three years of age.

Most females mate every year but the overall reproductive rate is low. Females are capable of producing litters every year when well-fed (such as in captivity) but most often produce every other year in the wild. The probability of a female reproducing is highly dependent on her condition in the winter.(2)(3)

Little more than half of a given litter will survive their first year, frequently less in trapped populations or in areas of significant human activity.(5)

Diet

Wolverines are scavengers and opportunistic hunters. Large ungulate carrion is a significant part of the diet particularly in the winter months, and small rodent prey may also be of seasonal importance. Nesting birds, insect larvae, and fish (wolverines are excellent swimmers) may be eaten as encountered. The entire carcass is consumed, bones included. Anything that cannot be eaten will be cached for later consumption, and bones may be buried during the warmer months to be dug back up over winter. Wolverines are well-adapted to winter scavenging: their jaws can crack open bones as thick as a moose’s femur; they can eat frozen meat with the aid of their warm breath and a special backward-facing molar; and they can locate a carcass buried under six metres of snow purely through scent.(2)(3)(13)(14)

Though primarily carnivorous, wolverines will consume berries when seasonally available and have been known to raid the seed and nut caches of squirrels and some bird species. Wolverine urine often contains conifer terpenes—plant oils that cannot be produced in animal bodies—and their droppings may contain conifer bark and needles, but it is currently unknown whether this plant matter is of nutritional importance or to what degree.(2)(3)

They are not particularly gluttonous

The wolverine’s reputation as a supposed habitual overeater is reflected in their scientific name Gulo gulo, meaning “glutton” twice. While they have large stomachs and can eat quite a lot in one sitting, this moniker is a bit unfair. Being a large mustelid in a frozen environment incurs a major caloric debt that must be repaid whenever the opportunity presents itself. “Gluttony” would usually imply a fondness for specifically unnecessary eating, and at any rate one will find that wolverines have very little body fat. Likewise their habit of eating every part of their prey—up to, and including, the bones—and caching whatever cannot be immediately eaten is not gluttony, but simple frugality in an unforgiving economy.

Predators and threats

Though sturdy and remarkably tenacious, wolverines are not as invulnerable as commonly portrayed. Wolves are major predators of wolverines(15), and bear and mountain lion attacks are fairly common sources of mortality. Young wolverines are especially vulnerable to predation.(2) Starvation, avalanches, territorial disputes with conspecifics, and even mountaineering accidents claim many wolverine lives per year.(2)(3) It is rare that a wolverine dies of old age.

Human activity has severely negatively impacted wolverine populations and continues to do so. Habitat fragmentation, property development, logging, hunting, and trapping has extirpated this species throughout much of its former range. Winter recreation disturbs denning mothers, an issue of increasing importance as snowmobiles and aviation allows humans to travel deeper into the winter landscape. Wolverine populations are very sensitive to trapping, even when not the target species.(2)(3) They are frequently persecuted, poached, even culled, even where populations are already considered vulnerable and “protected”.(16)(17)(18)

Disappearing snowpack is an issue of existential concern for the wolverine. Genetic bottlenecks and inbreeding depression caused by the isolation of small populations (such as in the scattered populations of the contiguous United States) may threaten the stability of larger metapopulations.

Conservation

Local and federal governments worldwide seem generally unwilling to afford this species due protection.(3) Though Mustelidae as a whole is remarkably adaptable and resilient, it is unclear if this indomitable symbol of wilderness has a future in the Anthropocene epoch.

As of November 2023, the U.S. Fish & Wildlife Service announced that the North American wolverine will receive federal protection as a threatened species under the Endangered Species Act.(19)

Geographic range

Body length: 65–107 cm / 26–42 in (males), 63–89 cm / 25–35 in (females)
Tail length: 17–26 cm / 6.7–10.2 in
Weight: 10.8–18.1 kg / 24–40 lb (males), 8–12 kg / 18–26 lb (females)
Lifespan: Up to 13 years (wild), up to 17 years (captivity)
Range: The arctic and boreal forests, tundras, and mountainous regions of the Northern Hemisphere.
Conservation status: Least concern (global), vulnerable (Europe)
Subfamily: Guloninae
Recognised subspecies(20)

  1. North American wolverine – (G. g. luscus)
  2. Eurasian wolverine – (G. g. gulo)

References

  1. Landa, Arild; Lindén, Mats & Kojola, Ilpo (2000). Action Plan for the conservation of Wolverines (Gulo gulo) in Europe (PDF)Nature and environment, No. 115. Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention). Archived (PDF) from the original on 29 April 2015. Accessed 22 February 2021.
  2. The Wolverine Foundation Editors [TWF]. 2012. Species Accounts. Accessed 08 January, 2023.
  3. Chadwick, D. 2010. “The Wolverine Way”.
  4. Nikolai E on YouTube. 2017. Wolverine VS Reindeer in a Blizzard. Accessed 10 January, 2023.
  5. Copeland, J., Yates, R. 2008. Wolverine Population Assessment in Glacier National Park. Accessed 10 January, 2023.
  6. Copeland, J. 1996. Biology of the wolverine in Central Idaho. p. 61. Accessed 10 January. 2023.
  7. Cain, J. “Jeff Cain”. Accessed 12 January, 2023.
  8. Fournier, A., Snowdon, W. CBC. 2016. Wolverines can be taught to sniff out avalanche survivors, trainer says. Accessed 10 January, 2023.
  9. Bonamy, Morgane, Thora Martina Herrmann, and Andrew Blair Harbicht. ‘I think it is the toughest animal in the North’: human-wolverine interactions among hunters and trappers in the Canadian Northwest Territories”. Polar Geography 43.1 (2020). p. 3.
  10. Knoblauch, J. Earthjustice. 2022. Keeping the Wolverine Wild in a Climate Crisis Accessed 10 January, 2023.
  11. Cahalane, V. 1961. Mammals of North America”. p. 195.
  12. Nowak, R. 1991. “Walker’s Mammals of the World” 5th Ed. Vol. II. p. 1125.
  13. Sletten, A. Terra Mater Factual Studios. 2021. Wolverine – One Tough Mother.
  14. PBS. 2010. Wolverine Facts. Accessed 10 January, 2023.
  15. White, K. S., Golden, H. N., Hundertmark, K. J., & Lee, G. R. (2002). Predation by Wolves, Canis lupus, on Wolverines, Gulo gulo, and an American Marten, Martes americana, in Alaska. Canadian Field-Naturalist, 116(1), 132–134.
  16. Jeffries, G. The New Humanitarian. 2017. Blight or Blessing? How the Wolverine Embodies Arctic Diversity Accessed 12 January, 2023.
  17. Duesund, J. NRK. 2016. Dette må vi slutte med (We have to stop this). Accessed 12 January, 2023.
  18. Lysvold, S. NRK. 2022. Ville dyr blir forgiftet, skutt og pint i hjel i brutale fotsakser – nær alle saker blir henlagt (Wild animals are poisoned, shot and tortured to death in brutal leg-hold traps – almost all cases are dropped. Accessed 12 January, 2023.
  19. Smith, Amanda. U.S. Fish & Wildlife Service. 29 November, 2023. North American wolverine receives federal protection as a threatened species under the Endangered Species Act. Accessed 23 November, 2023.
  20. Copeland, J.P. and J.S. Whitman. 2003. Wolverine (Gulo gulo). Pages 672-682 in “Wild Mammals of North America: Biology, Management, and Economics”. G.A. Feldhamer, B.C. Thompson, and J.A. Chapman, editors. The Johns Hopkins University Press. Baltimore, Maryland USA.

What Are Mustelids?

Badgers | Ferret-Badgers | Fisher | Grisons | Martens | Otters | Tayra | Weasels | Wolverine