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Wolverine (Gulo gulo)

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COSEWIC
Executive Summary

Wolverine
Gulo gulo

Species Information

Wolverines are a medium-sized carnivore and the largest terrestrial member of the weasel family in North America, appearing more like small bears than weasels. A single subspecies of wolverine ranges across most of Canada. Further studies are required to determine if the Vancouver Island population is a separate subspecies. Several wolverine populations may be isolated from the main population, including those of the arctic and Pacific islands, and that of Quebec and Labrador.

Distribution

Wolverines are found across northern Eurasia and North America. In Canada they are found in northern forested wilderness areas across the country, in alpine tundra of the western mountains, and in arctic tundra. They formerly occupied habitats that were disturbed by humans in the Prairie Provinces and eastern Canada.

Habitat

A wide variety of forested and tundra habitats is used by wolverines in wilderness areas. Habitats must have an adequate year-round supply of food that consists of smaller prey species, such as rodents and snowshoe hares, used more in summer, and the carcasses of larger animals, like moose and caribou, which are an important part of the winter diet. Females den at higher elevations under rocks, logs or snow. The snow cover must persist late into the spring to insulate the den and food must be close at hand. Forestry, hydroelectric developments, oil and gas and mineral exploration and development, and transportation corridors continue to alter, remove or fragment habitats. About 6% of all current wolverine range is within parks and protected areas, and 10% of the best habitats in western Canada are protected.

Biology

Most females do not breed until they are 2 years old, and thereafter they do not breed every year. Litter sizes average about 3 kits. Wolverines breed in the summer when females are more sedentary, with the implantation of the blastocyst delayed until winter. Wolverines face mortality from predation and starvation. Human-caused mortality factors, such as trapping, hunting and road/railway kill, are also significant, and may increase as settlement of remote areas increases. The growth rate of kits is rapid, placing nutritional demands on the mother. They occupy home ranges which can be 50-400 km2 for females and 230-1580 km2 for males. Juveniles may have even larger ranges and can disperse over 300 km. Home ranges may overlap within and between sexes but, overall, wolverine densities are low; about 5/1000 km2 in good habitats. Wolverines are scavengers and predators, often caching food for future use.

Population Sizes and Trends

Population size is difficult to estimate; however, combined estimates of about 9 200 wolverines for the Yukon, British Columbia and Manitoba may be extrapolated to 15 000 to 19 000 across Canada, based on areas of occupancy and relative densities. Pre-trapping population estimates likely exceed 20 000. Wolverine populations in many areas of Canada are benefiting from the cessation of wolf poisoning and wolf control, harvest closures, advanced trapline and harvest management systems and ungulate (e.g., caribou) population gains. Wolverine range continues to decline in northern Ontario; however, recent increases have been noted in northwestern Ontario and Manitoba, where caribou have increased. The populations are stable and healthy elsewhere, except locally in Alberta and British Columbia, where caribou have declined. Wolverine, possibly a separate subspecies, may be extirpated from Vancouver Island. The eastern wolverine population is either extremely scarce or extirpated.

Limiting Factors and Threats

The ability of wolverine populations to recover and repopulate vacant habitats is naturally low. Other factors limiting populations include harvest, including trapping on the periphery of protected areas, disruptions to important ecosystem components such as wolves, moose and caribou, disturbance of denning areas by recreational users, and threats to habitats. Habitat fragmentation in southern areas may destabilize populations.

Special Significance of the Species

Wolverines are indicators of ecosystem health. Populations are considered vulnerable worldwide. The fur is valued for its frost-resistant properties. Aboriginal peoples have viewed wolverines as both spiritual guides and relentless enemies. A mythology and folklore exist around the wolverine’s ferocity and cunningness.

Existing Protection or Other Status Designations

The eastern population is not harvested, and the western population is harvested in all jurisdictions except Ontario, with some regional closures in place. The provincial and CDC rankings are: critically imperilled in Quebec, endangered in Labrador, threatened in Ontario, and vulnerable or sensitive throughout most of the west and north. Wolverines on Vancouver Island are considered critically imperilled by the provincial government.