Wolverine (Gulo Gulo)
The wolverine /ˈwʊlvəriːn/, Gulo gulo (Gulo is Latin for “glutton”), also referred to as glutton, carcajou, skunk bear, or quickhatch, is the largest land-dwelling species of the family Mustelidae (weasels). It is a stocky and muscular carnivore, more closely resembling a small bear than other mustelids. The wolverine, a solitary animal, has a reputation for ferocity and strength out of proportion to its size, with the documented ability to kill prey many times larger than itself.
The wolverine can be found primarily in remote reaches of the Northern boreal forests and subarctic and alpine tundra of the Northern Hemisphere, with the greatest numbers in northern Canada, the U.S. state of Alaska, theNordic countries of Europe, and throughout western Russia and Siberia. Their populations have experienced a steady decline since the 19th century in the face of trapping, range reduction and habitat fragmentation, such that they are essentially absent in the southern end of their European range.
Within the Gulo genus, a clear separation occurs between two subspecies: the Old World form Gulo gulo gulo and the New World form G. g. luscus. Some authors had described as many as four additional North American subspecies, including ones limited to Vancouver Island (G. g. vancouverensis) and the Kenai Peninsula in Alaska (G. g. katschemakensis). However, the most currently accepted taxonomy recognizes either the two continental subspecies or recognize G. gulo as a single Holarctic taxon.
Recently compiled genetic evidence suggests most of North America’s wolverines are descended from a single source, likely originating from Beringia during the last glaciation and rapidly expanding thereafter, though considerable uncertainty to this conclusion is due to the difficulty of collecting samples in the extremely depleted southern extent of the range.
The adult wolverine is about the size of a medium dog, with a length usually ranging from 65–107 cm (26–42 in), a tail of 17–26 cm (6.7–10.2 in), and a weight of 9–25 kg (20–55 lb), though exceptionally large males can weigh up to 32 kg (71 lb). The males are as much as 30% larger than the females and can be twice the females’ weight. Shoulder height is reported from 30 to 45 cm (12 to 18 in). It is the largest of terrestrial mustelids; only the marine-dwelling sea otter and giant otter of the Amazon basin are larger.
Wolverines have thick, dark, oily fur which is highly hydrophobic, making it resistant to frost. This has led to its traditional popularity among hunters and trappers as a lining in jackets and parkas in Arctic conditions. A light-silvery facial mask is distinct in some individuals, and a pale buff stripe runs laterally from the shoulders along the side and crossing the rump just above a 25–35 cm (9.8–13.8 in) bushy tail. Some individuals display prominent white hair patches on their throats or chests.
Like many other mustelids, it has potent anal scent glands used for marking territory and sexual signaling. The pungent odor has given rise to the nicknames “skunk bear” and “nasty cat.” Wolverines, like other mustelids, possess a special upper molar in the back of the mouth that is rotated 90 degrees, towards the inside of the mouth. This special characteristic allows wolverines to tear off meat from prey or carrion that has been frozen solid.
Diet and hunting
The wolverine is a powerful and versatile predator and scavenger. Prey mainly consists of small to medium-sized mammals, but the wolverine has been recorded killing prey such as adult deer that are many times larger than itself. Prey species include porcupines, squirrels, beavers, marmots, rabbits, voles, mice, shrews, lemmings, caribou, roe deer, white-tailed deer, mule deer, sheep, moose, and elk. Smaller predators are occasionally preyed on, including martens, mink, foxes, Eurasian lynx, weasels, and coyote and wolf pups. Wolverines have also been known to kill Canadian lynx in the Yukon of Canada. Wolverines often pursue live prey that are relatively easy to obtain, including animals caught in traps, newborn mammals, and deer (including adult moose and elk) when they are weakened by winter or immobilized by heavy snow. Their diets are sometimes supplemented by birds’ eggs, birds (especially geese), roots, seeds, insect larvae, and berries. A majority of the wolverine’s sustenance is derived from carrion, on which they depend almost exclusively in winter and early spring. Wolverines may find carrion themselves, feed on it after the predator is done feeding (especially wolf packs) or simply take it from another predator. Whether eating live prey or carrion, the wolverine’s feeding style appears voracious, leading to the nickname of “glutton” (also the basis of the scientific name). However, this feeding style is believed to be an adaptation to food scarcity, especially in winter.
Armed with powerful jaws, sharp claws, and a thick hide, wolverines, like most mustelids, are remarkably strong for their size. They may defend kills against larger or more numerous predators such as wolves or bears. At least one account reported a wolverine’s apparent attempt to steal a kill from a black bear, although the bear won what was ultimately a fatal contest. In another account, a wolverine killed a polar bear. Wolverines are known to follow wolf and lynx trails, purportedly with the intent of scavenging the remains of their kills. Wolves are thought to be their most important natural predator, with the arrival of wolves to a wolverine’s territory presumably leading the latter to abandon the area.
Wolverines inhabiting the Old World (specifically, Fennoscandia) hunt more actively than their North American relatives. This may be because competing predator populations in Eurasia 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 changes in wolf populations may affect the population of wolverines. They are also known on occasion to eat plant material.
Mating and reproduction
Successful males will form lifetime relationships with two or three females, which they will visit occasionally, while other males are left without a mate. 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 gestation period is 30–50 days, and litters of typically two or three young (“kits”) 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) 13 years. Fathers make visits to their offspring until they are weaned at 10 weeks of age; also, once the young are about six months old, some reconnect with their fathers and travel together for a time.
Wolverines live primarily in isolated arctic and alpine regions of northern Canada, Alaska, Siberia, and Scandinavia; they are also native to European Russia, the Baltic countries, the Russian Far East, northeast China and Mongolia. In 2008 and 2009, wolverines were sighted as far south as the Sierra Nevada, near Lake Tahoe, for the first time since 1922. They are also found in low numbers in the Rocky Mountains and northern Cascades of the United States, and have been sighted as far south and east as Michigan. However, most New World wolverines live in Canada.
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