The Wolverine (Gulo gulo) is the biggest type of weasel found in Ontario. Some common names associated with the wolverine are devil bear, skunk bear and devil beast. The wolverine is listed as a threatened species under Ontario’s Endangered Species Act, 2007 (ESA) and is protected from being killed, captured or taken in Ontario. The wolverine is classified as a furbearer under the Fish and Wildlife Conservation Act, but hunting/trapping is closed in all areas.
The wolverine is broadly distributed through boreal and tundra habitats in North America and Eurasia. Historically, wolverines occurred throughout much of Ontario; however this range has receded northward. At present, wolverines are confined to the northern Boreal Forest in the northwestern portion of the province. They seem to have disappeared fairly rapidly from southern Ontario in the 1800s and early 1900s during a period characterized by a large increase in human settlement, logging and railroad construction.
The wolverine is about the size of a medium-sized dog. This short-legged, stocky animal resembles a cross between a badger, a skunk and a small bear. It has dark fur, ranging in colour from brown to black with a shaggy appearance, sometimes carrying light patches on its chest, neck and chin. A broad band of lighter-coloured fur usually extends along its flanks, meeting at the base of its long, bushy tail. Its head is broad and rounded, with black extending from the eyes to the tip of the snout and it often has a light-coloured band across the forehead. It has a short, stout neck, broad forehead, small eyes and short, rounded ears. Adult males usually weigh 14 to 21 kg (30 to 46 lbs) and females 7 to 14 kg (15 to 30 lbs). The length of the body of adults ranges from 65 to 105 cm (26 to 41 in); the tail varies from 17 to 26 cm (6.5 to 10 in).
Wolverines generally reproduce fairly slowly. The females do not usually reproduce successfully until they are three to four years old. Although they can have litters in consecutive years, they often skip a year. The average litter has two or three kits. Wolverines breed from May to August and are polygamous. Females are believed to have only one breeding season per year. Like most mustelids, wolverines exhibit delayed implantation, with implantation occurring as early as November or as late as March. Wolverines in the wild have a normal life expectancy of 8 to 12 years. Occasionally they live longer than that, and they are known to have successful litters at 12 years of age. Most known recorded deaths of wolverines in North America are due to trapping/hunting, motor vehicles or trains, predation (mostly by wolves, mountain lions and other wolverines) and starvation.
Wolverines are habitat generalists throughout North America, occupying both forested and open habitats and occurring well above tree line in mountainous areas. In Ontario, they live in boreal and tundra forests. The main requirements for wolverine habitat are remoteness from human settlement, persistent snow cover through the denning season and consistently available food source, particularly carrion. Habitat requirements for den sites tend to be more specific, with denning mothers using areas that provide protection from predators, human disturbance, adequate insulation and enough prey for rearing kits. Dens are generally constructed at some distance from human activity and placed under fallen or blown down trees covered in snow, burrows, caves, overhanging banks or in tunnels in snowdrifts.
Food and Feeding Behaviour
Wolverines are able to exploit a wide variety of foods, but can best be called “scavenging predators” that rely mostly on scavenging during the winter. They are generally carnivorous however, in times when food is scarce they will feed on fruits, berries, insects and fish. In some instances, wolverines are able to kill larger animals such as deer, moose or caribou; however, predation on the larger animals is low. The wolverine depends highly on scavenging caribou, moose and deer carcasses as a primary food source. They have also been known to steal trapped furbearers and their bait. They also rely on a variety of small mammals and birds, such as rabbits, squirrels, mice, voles, ptarmigan, and grouse. This food sources is particularly important while caring for their young in the spring and summer, when their movements are restricted to the area around their dens and rendezvous sites where mothers leave their kits while they hunt. In Ontario, there is evidence that beaver may also be favoured prey of wolverines. The ability to obtain enough food in winter is considered critical to successful female reproduction. It is important to note that wolverines ten to cache surplus food items.
Wolverines are solitary and they range over vast areas. Even under the best conditions, wolverine densities are naturally low compared to those of other similar-sized carnivores, ranging from 2.2 to 20.8 per 1000 km² (386 sq mi). In Ontario, the winter home ranges fall at the high end of those sizes. Home ranges of a male and female may overlap. It is also common for the home ranges of wolverines of the same sex to at least partly overlap. Wolverines are regarded as symbols of the wilderness and have inspired nearly mythic tales of their strength, ferocity and destruction of cabins and food caches. That dramatic reputation, which is deeply rooted in legends and folklore, is largely undeserved as most wolverines will go about their own business. By virtue of their scavenging habits however, wolverines can and do have conflicts with humans.
The wolverines may be the least understood of North America’s medium-sized to large carnivores. It is quite recently that we have begun to learn more about this species and the way that human activities may influence wolverine populations. The threats to wolverines, together with the limited resilience of this species, are degradation and fragmentation of habitat, increased encounters with other competitors and predators, over-harvesting potential and disturbance by humans.