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TaxonomyThe wolverine is classified into the Kingdom Animalia, the Phylum Chordata, the Class Mammalia, the Order Carnivora, and the Family Mustelidae. The next 2 steps down, the Genus and species are generally what make up what we call the animal's scientific name. We also sometimes use the lowest level, the subspecies name as well. For the wolverine, the Genus is Gulo and the species name is also gulo. For the Old World, or European wolverine, the subspecies name is gulo as well (Gulo gulo gulo), while for the New World, or North American species, we use the subspecies name luscus (Gulo gulo luscus). 
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DescriptionThe wolverine is the largest land-dwelling member of the family Mustelidae. The wolverine is powerfully built, and well adapted for winter survival. The wolverine walks on the soles of its feet as do bears and humans. This is called a plantigrade posture and allows the animal to move much easily through soft, deep snow. The skull of the wolverine is heavily built and its teeth are large and strong. Along with powerful jaw muscles, the wolverine can easily feed on frozen meat and bone. The dental formula of the wolverine is incisor 3/3, canine 1/1, premolar 4/4, molar 1/2 for a total of 38 teeth. The wolverine's head is broad and rounded, with small eyes and short rounded ears. Its legs are short, with five toes on each foot. By weight, males are typically 30-40% larger than females with males generally weighing 11 to 18 kg and females 6 to 12 kg. Wolverine fur is typically a thick, glossy dark brown. A light, silvery facial mask is obvious in some individuals with a pale buff stripe running from the shoulders along the animal's side and crossing the rump just above a long, bushy tail. A white hair patch on the neck and chest is often present in some individuals while not occurring in others. White hair on the toes, feet and forelegs is not uncommon. Wolverine communicate through vocalizations and scent-marking. Scent-marking, or chemical communication is accomplished with urine and abdominal rubbing. Although wolverine have well developed anal musk glands, musking appears to be used primarily as a fear-defense mechanism. The most common example of this occurs with the skunks.
DistributionThe wolverine has a world-wide distribution that encompasses the arctic and extends into the subarctic areas of the northern hemisphere. In the past, the wolverine's North American distribution included the northern part of the continent southward to the northernmost edge of the United States from Maine to Washington state. It extended south along the Cascade Mountains through Oregon into the southern Sierra Nevada Mountains in California and along the Rocky Mountains into Arizona and New Mexico. Records of the wolverine within the upper midwest apparently pre-date human settlement, with the animal most likely absent from this area and the northern plains states by the early 1900's. While the State of Michigan is called "The Wolverine State," there are very few records of the wolverine ever being present in Michigan. Currently, the wolverine is known to be present in Washington, Idaho, Montana, and Wyoming. It is thought to still occur in Oregon, but its presence is not confirmed. The wolverine's status also is presently unknown in California, Colorado and Utah, although there are occasional unconfirmed reported sightings. In Canada, the wolverine is present in boreal forests form east to west, and as far north as Ellesmere Island. Until the turn of the century, the wolverine inhabited much of eastern Canada except for Prince Edward Island, Nova Scotia, Newfoundland, eastern New Brunswick, Gaspe Peninsula, and Anticosti Island. Presently, the wolverine is extremely rare in Quebec and Ontario, and there are no recent records from Labrador. In Manitoba and Saskatchewan, numbers appear to have declined, the southern limits have receded to the north, and wolverine are now confined to the northern portions of the provinces. In Alberta, the species once occurred in all coniferous forests of the province, but now is found only in remote areas in the north and in the Rocky Mountains. Wolverine occur throughout mainland British Columbia, except for the southern agricultural areas, and throughout the Yukon Territory and mainland Northwest Territories. They occur continuously in mainland Alaska but only on some of the southeastern islands. In Eurasia, the wolverine is found from Scandinavia eastward through eastern Europe, Siberia, and Asia. Most animals are concentrated in the mountain chain of northern Norway and Sweden, and along the south-central Norwegian mountains. In Sweden, wolverines are restricted to remote areas in the northwest. The numbers appear to be increasing however. Wolverines are also found in the tundra and forest zones of eastern Europe, Russia, and northern Asia. In western Siberia, wolverines are widely distributed in the tundra and taiga, and are relatively common in extreme eastern Russia.
ReproductionThe mating system of the wolverine appears to be polygamous, which means mating with more than one of the opposite sex. Wolverine generally become reproductively active from May to August. Wolverine pairs may remain together for several days during the mating period. Wolverines use a reproductive strategy called delayed implantation. Once the egg of the female is fertilized, it will grow to a multi-cell stage called a blastocyst which is about the size of the head of a pin. The egg then stops growing and remains in this state for 6 to 8 months until it is ready to implant in the uterine wall. This happens sometime from November to January. From that point, it takes the egg (or embryo) 30-50 days to complete the gestation period. The young are then born sometime from January through April, with most females giving birth before late March. Litter size averages 2-3. Baby wolverine are called kits or cubs. They are born fully furred with their eyes closed and teeth not yet erupted. At birth their fur is all white, they weigh an average of 84.0 grams, and have a head to rump length of about 120 mm. They will remain with the mother until weaning at 9-10 weeks, but she may move them to several different dens before then. These movements may be because of den snow melt, or she may be moving them to avoid discovery by other predators. The young will begin to travel with their mother by late-May. Adult size is often reached by early the next winter. The young may attempt to disperse on their own the following year, or they may remain with their mother, brothers or sisters, and even near their father until they are mature enough to find a mate of their own. This occurs at about 2 years of age.
DenningScandinavian research provides the earliest data on winter denning habits of wolverine. Most dens in a Finland study occurred on bare, rocky hillsides of mountain slopes near or above timberline, while 6 dens were located in lower elevation spruce and pine peat-bogs. Most of 28 dens in Norway were found above timberline in deep snow near cliff areas. The general structure of dens in both studies was the same. Den entrances were located in soft snow near trees or rocks, with a tunnel extending straight down 1-5 meters to ground level. Lateral tunnels extended for up to 50 meters along the ground surface. In most cases, wolverine kits were found at ground level on bare soil. Data on wolverine denning habits in North America are limited. A few dens have been described in Alaska. Two were above timberline in snow filled ravines while the third was found in an abandoned beaver house. Magoun (1985) provided data on the natal dens of 2 females in tundra habitat of northwest Alaska. Audrey Magoun, who conducted research on wolverine in Arctic Alaska, described den entrance tunnels extending less than 2 meters beneath the snow surface to den systems of up to 50 m in length. The dens used by 2 female wolverine in an Idaho study were found in high elevation talus rock habitats. The females dug down through as much as 10 feet of snow to access natural tunnels and chambers that occurred under very large boulder fields in subalpine glacial basins.
Mortality - what causes wolverines to die?Humans cause the majority of deaths in wolverine, occurring in areas where wolverine are trapped for sport or commercially. Aside from human-caused mortality, starvation and predation appear to be primary causes of death. Wolverine are commonly scavengers, which often times results in encounters with other predators. While wolverine are certainly capable of defending themselves in most instances, they are still relatively small animals in comparison with other large predators such as bear, wolves, and mountain lions. In encounters with such predators, the wolverine will occasionally be killed. Starvation most likely accounts for some mortality when wolverine become old and not as able to travel and find food.
Density - how many wolverine are there?In general, wolverine densities are low when compared to carnivores of similar size. Estimates of population numbers are generally not found in the scientific literature as wolverine are extremely difficult to count. Researchers have made estimates of population density based on how many individual wolverine may populate a particular area that they have studied. These estimates generally suggest that it may take an area from 40 kmē to 800 kmē to provide adequate habitat for a single wolverine. Until a better way to count, or census wolverine can be developed, we can only rely on these general estimates of population density.
Spatial Use - Home RangeSpatial Use is a term we use to describe the area that a wolverine needs to live its life. This area is often referred to as an animal's home range. We might describe a home range for a particular season, such as a winter or summer home range, for a complete year, or for the animal's entire life. We also use home range studies to look at how an individual animal may interact with neighboring animals - whether the home ranges overlap or whether they are exclusive which may indicate the individual will not tolerate the trespass of another individual. All this helps us understand how much area a wolverine needs in a particular type of habitat and how it relates to others of its own kind during a particular part of its life. Generally, we know that males have larger home ranges than females, females without kits have larger home ranges than females with kits, and home range use appears to change with season. The size of a wolverine home range appears to vary depending on what type of habitat the animal uses. Alaska wolverine researchers reported annual home ranges size for male wolverines varying from a little over 500 kmē to nearly 700 kmē. Home ranges for Yukon male wolverine were somewhat smaller at just under 400 kmē. Montana wolverine used areas just over 400 kmē while Idaho wolverine displayed the largest spatial requirements with resident male home ranges averaging 1,522 kmē. Female home ranges varied from 104 kmē in Alaska to 388 kmē in Montana.
Home range overlapWithin most of the wolverine research projects, it was found that wolverine appear to use a spacing system referred to as intrasexual exclusion. Intra means within and exclusion means to avoid, so what this suggests is that wolverine of the same sex tend to avoid one another, while wolverine of the opposite sex may overlap their home ranges. This is why an adult male may have the home ranges of several females within his home range. These exclusive home ranges generally don't develop until the individuals have matured and found an area to develop their own home range.
Food HabitsWolverine would probably not be present without healthy populations of large herbivores such as deer, elk, moose, and caribou. These species make up the bulk of the wolverine's diet most of the year and are typically consumed as carrion. Wolverine will rely on smaller species for food as well. In Arctic Alaska, ground squirrels were most common in late winter and spring diets, while snowshoe hare comprised a large portion of the wolverine's diet in Yukon. Vegetation such as berries and fruits have been reported in the wolverine's diet, but they are probably not as important as a diet comprised primarily of meat. In Idaho, wolverine were reported using ants and other insects. If eaten in large quantities, insects can provide considerable protein but they are probably not an important component of the wolverine's diet.
Habitat UseWolverine habitat is most generally considered to be boreal, subalpine forest and arctic tundra. This generally means that wolverine prefer high elevation forested or tundra habitats occurring across the northern hemisphere. Wolverine tend to prefer higher elevation, alpine habitats during summer months, and lower elevation timbered habitats during winter. Researchers believe these preferences are related to the availability of food. Wolverine seek out ground squirrel and marmots in high elevation talus areas as these species come out of hibernation in spring and early summer. Wolverine move to lower elevation habitats in winter where carrion (or the carcasses of dead elk, deer, moose and reindeer) is more easily found.
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