The wolverine (Gulo gulo
) is the largest land-dwelling species of the Mustelidae or weasel family (the Giant Otter is largest overall), and is the only species currently classified in the genus Gulo
(meaning "glutton"). It is also called the Glutton or Carcajou. Some authors recognize two subspecies: the Old World form Gulo gulo gulo
and the New World form G. g. luscus
. A third subspecies limited to Vancouver Island (G. g. vancouverensis
) is also occasionally described. However craniomorphic evidence suggests that the Vancouver Island wolverines are properly included within G. g. luscus
The wolverine (Gulo) is a stocky and muscular animal, considered carnivorous but known on occasion to eat plant material. It has glossy brown hair with stripes of dull yellow along the sides. Its fur is long and dense and does not retain much water, making it very resistant to frost, which is common in the wolverine's cold habitat. (For these reasons, the fur has been traditionally popular among hunters and trappers as a lining in jackets and parkas, especially for wear in Arctic conditions). The adult wolverine is about the size of a medium dog, with a length usually ranging from 65-87 cm (25-34 inches), a tail of 17-26 cm (7-10 inches), and weight of 10-30 kg (22-66 lb). Males are as much as 30 percent larger than the females. In appearance the wolverine resembles a small bear with a long tail. It has been known to give off a very strong, extremely unpleasant odor, giving rise to the nicknames "skunk bear" and "nasty cat." Wolverines, as other mustelids, possess a special upper molar in the back of the mouth that is rotated 90 degrees, or sideways. This special characteristic allows wolverines to tear off meat from prey or carrion that has been frozen solid and also to crush bones, which enables the wolverine to extract marrow.
The wolverine is, like most mustelids, remarkably strong for its size. It has been known to kill prey as large as moose, although most typically when these are weakened by winter or caught in snowbanks. Wolverines inhabiting the Old World (specifically, Fennoscandia) are more active hunters than their North American cousins. This may be because competing predator populations are not as dense, making it more practical for the wolverine to hunt for itself than to wait for another animal to make a kill and then try to snatch it. They often feed on carrion left by wolves, so that changes in the population of wolves may affect the population of wolverines.
Armed with powerful jaws and a thick hide, wolverines may defend kills against larger or more numerous predators. There is at least one published account of a 27-pound wolverine's attempt to steal a kill from a much larger predator—namely, a black bear (adult males weigh 400 to 500 pounds). Unfortunately for the mustelid, the bear won what was ultimately a fatal contest, crushing the wolverine's skull.
Mating season is in the summer, but the actual implantation of the embryo (blastocyst) in the uterus is stayed until early winter, delaying the development of the fetus. Females will often not produce young if food is scarce. The young (typically two or three) are born in the spring. Kits develop rapidly, reaching adult size within the first year of a lifespan that may reach anywhere from five to (in exceptional individuals) thirteen years.
Adult wolverines have no natural predators, save man, though they do come into conflict with (and may be killed by) other large predators over territory and food. Juveniles are of course more vulnerable; infants (kits) have been known on occasion to be taken by predatory birds such as eagles.
Wolverine on rockThe wolverine lives primarily in isolated northern areas, for example the arctic and alpine regions of Alaska, northern Canada, Siberia and Scandinavia; they are also native to Russia and the Baltic countries. The wolverine is found as far south as the Sierra Nevada in California and a few remain in the Rocky Mountains and northern Cascades of the United States.
The world's total wolverine population is unknown. The animal exhibits a low population density and requires a very large home range, covering hundreds of miles in a few days. The range of a male wolverine can be more than 620 km² (240 sq mi) while encompassing the ranges of several females (with smaller home ranges of roughly 130-260 km² (50-100 sq mi). Adult wolverines try for the most part to keep non-overlapping ranges with adults of the same sex. Radio tracking suggests an animal can range hundreds of miles in only a few months.
This requirement for large territories brings wolverines into conflict with human development, and hunting and trapping further reduce their numbers, causing them to disappear from large parts of their former range; attempts to have them declared an endangered species have met with little success.