Montana Field Guide

Wolverine - Gulo gulo

The wolverine is a bear-like mustelid with massive limbs and long, dense, dark brown pelage, paler on the head, with two broad yellowish stripes extending from the shoulders and joining on the rump. Variable white or yellowish markings are often present on the throat and chest. The tail is bushy. The feet are relatively large (6.5 to 11.3 centimeters total length) with robust claws. Wolverines weigh between 7 and 32 kilograms and range from 0.9 to 1.1 meters in length. Females average about 10% less than males in linear measurements and 30% less in mass (Hall 1981, Ingles 1965, Nowak 1991).

Wolverines are most similar to fishers (Martes pennanti) but are nearly twice as large. Fishers also lack the light colored lateral markings of the wolverine and the tail is less bushy. Badgers have shorter legs and are much lighter colored with a distinctive black and white pattern on the face.

Montana Range

Wolverines in northwestern Montana and Alaska tended to occupy higher elevations in summer and lower elevations in winter (Hornocker and Hash 1981, Whitman et al. 1986).
Seasonal ranges were all within a large home range; dispersal movements of more than 300 kilometers are known (Magoun 1985, Gardner et al. 1986).

Wolverines are limited to alpine tundra, and boreal and mountain forests (primarily coniferous) in the western mountains, especially large wilderness areas. However, dispersing individuals have been found far outside of usual habitats. They are usually in areas with snow on the ground in winter. Riparian areas may be important winter habitat. When inactive, wolverines occupy dens in caves, rock crevices, under fallen trees, in thickets, or similar sites. Wolverines are primarily terrestrial but may climb trees.

In Montana, Hornocker and Hash (1981) found most wolverine use in medium to scattered timber, while areas of dense, young timber were used least. Wolverines avoided clearcuts and burns, crossing them rapidly and directly when they were entered at all. Hash (1987) reported wolverines in the Northern Rocky Mountain region were associated with fir, pine, and larch. Aspen stands were also used, as were cottonwoods in riparian areas. Ecotonal areas appeared to be important habitat components (Hash 1987). Hatler (1989) believed wolverines are not dependant on any particular vegetative habitat type. Banci (1986) reported "habitat requirements appear to be large, isolated tracts of wilderness supporting a diverse prey base, rather than specific plant associations or topography." South of the boreal forest, most habitat descriptions in the literature agree with Grove's (1988) characterization of "large, mountainous, and essentially roadless areas."

Wolverines are opportunistic. They feed on a wide variety of roots, berries, small mammals, birds' eggs and young, fledglings, and fish (Hatler 1989). They may attack moose, caribou, and deer hampered by deep snow. Small and medium size rodents and carrion (especially ungulate carcasses) often make up a large percentage of the diet. Prey is captured by pursuit, ambush, digging out dens (Biosystems Analysis 1989), or climbing into trees. They may cache prey in the fork of tree branches or under snow.

Wolverines are generally solitary and wide-ranging. They occur at relatively low densities (e.g., 1 per 65 square kilometers in northwestern Montana) (Hornocker and Hash 1981). Home ranges of males are larger than those of females, with home ranges of up to several hundred square kilometers. The mean annual home range of males was 535 square kilometers in Alaska, and 422 square kilometers in Montana. Female home ranges were 105 square kilometers in Alaska and 388 square kilometers in Montana (Hornocker and Hash 1981). Males in some areas apparently are territorial, but in Montana there was extensive overlap of the ranges of both the same and opposite sexes (Hornocker and Hash 1981). Apparently territory/range size depends on availability of denning sites and food supply (Wilson 1982). Some individuals travel regularly over the same route (Wilson 1982). Available evidence indicates that juveniles disperse usually around 30 to 100 kilometers from their natal range, though dispersal movements of more than 300 kilometers are known (Magoun 1985, Gardner et al. 1986). There are no important predators other than humans.

Although the wolverine usually breeds in summer, the event may occur from April to October. Implantation is delayed and does not occur until winter. Gestation lasts 7 to 9 months; active gestation is 30 to 40 days. One to six (usually 2 to 4) young are born January through April, mainly in February or March, and reportedly April through June in the Pacific states (Ingles 1965), in a den among rocks or tree roots, in a hollow log, under a fallen tree, or in dense vegetation, including sites under snow. Young are weaned beginning at about 7 or 8 weeks, and separate from the mother in the fall. They are sexually mature generally in the second or third year. Males sexually mature sometimes as yearlings (Alaska and Yukon); males over three years old were sexually mature in British Columbia. Some females mature at 12 to 15 months and produce their first litter when two years old (Wilson 1982). In some areas, females may produce litters only every 2 or 3 years. In British Columbia, most mature females were reproductively active. The wolverine lives to an age of up to about 10, or sometimes 15 to 18, years.

Wolverines were nearly extinct in Montana during the early 1900's and have been increasing in numbers and range since. Recovery originated in northwestern Montana and subsequently spread to its current range (Newby and Wright 1955, Newby and McDougal 1964). Wolverines are classified as a furbearer in Montana. Trapping regulations allow for one wolverine to be taken per person each season. Carcasses of trapped wolverines must be turned in to designated Fish, Wildlife and Parks employees in the trapping district in which the animal was taken, within five days of harvest.