Wolverine
Description
Although the wolverine Gulo gulo belongs
to the weasel family, Mustelidae, it is not long and lean like a weasel,
but short and thick, like a small bear. Its head is broad and round, with
small eyes and short rounded ears. Its legs are short and sturdy, with
five toes on each foot. Its long, curved claws are semi-retractile, which
means they can be partly drawn back in, and they are used for climbing
and digging. Its teeth are strong, and its head, neck, and shoulder muscles
are well developed. These adaptations allow the wolverine to feed on frozen
flesh and bone, and they provide a clue as to how wolverines survive.
An adult wolverine is about the size
of a medium-sized dog. Adult males weigh about 12 to 18 kg, adult females
about 8 to 12 kg. Wolverines that live in the north of their range are
usually larger than those living farther south.
The wolverine has one of the most
striking pelts of all fur-bearing animals. Its fur is typically a rich,
glossy, dark brown. Two pale yellow stripes originate at the nape of its
neck and sweep along each flank to merge at the base of its long, bushy
tail. White or orange patches are common on the chest or throat. The wolverine’s
toes, forepaws, or legs may occasionally be marked with white.
Habitat and habits
Within its range, the wolverine occupies
many different kinds of habitats. Wolverines generally prefer remote areas,
far away from humans and their developments. However, the specific characteristics
of the wilderness that the wolverine depends upon are not yet known. Labrador
and Quebec, for example, have not been recolonized by wolverines, despite
the abundance of caribou and undisturbed habitat. This lack of knowledge
about wolverine habitat makes it difficult for wildlife managers to manage
the species and protect its habitat.
One specific type of habitat wolverines
need is the den used by the female to give birth and raise her kits. Finding
such a den is difficult. Most dens that have been found are in tundra regions
and consist of a complex of snow tunnels associated with boulders or rocks.
The configuration of the rocks results in natural cavities under the snow,
which form dens for the wolverines.
Studies are expensive and difficult
to conduct because of wolverines’ large home ranges and low densities.
It is not surprising that we are still learning about the biology and behaviour
of this species. Some of the mysteries have been dispelled with the help
of studies in Alaska, Montana, British Columbia, Yukon, and Nunavut of
wolverines equipped with collars that allow their movements to be monitored
using satellites.
The home range of an adult wolverine
extends from less than 100 km2 for females to over 1 000 km2 for males.
These home ranges are the largest reported for a carnivore of this size,
and in many areas they rival the home ranges of bears, wolves, and cougars.
The size of the home range varies depending on the availability of food
and how it is distributed across the landscape — the more food there is,
the smaller the home range needs to be.
The density of wolverines ranges from
one individual per 40 km2 to one per 800 km2. Those regions that have the
most different kinds of habitat and prey, particularly those that include
large ungulates, or animals with hooves, contain the most wolverines. The
mountainous and forested areas of British Columbia and Yukon have the highest
densities, although these numbers are still low compared with the densities
of other carnivores. Densities of wolverines in Manitoba and Ontario are
lower. The rarity of wolverines becomes readily apparent when their density
is compared with the density of other solitary carnivores: one coyote per
0.5 to 10 km2 and one grizzly bear per 1.5 to 260 km2.
Wolverines can travel long distances
during their daily hunting activities, up to 40 km, with males travelling
farther than females. They have traditional routes, and they revisit the
same places every year. Wolverines are constantly on the move, unless they
have found a kill site. The young leave their home range, or disperse,
when they become sexually mature, at about one or two years of age. These
dispersal movements can be extensive, 300 km and more for young males.
The young females settle within or next to the area where they were born.
The wolverine is known by a variety
of descriptive names, including “skunk-bear,” because it marks its food
and various landmarks with urine and musk, a fluid secreted from its anal
glands, and “glutton,” because of its voracious appetite.
The wolverine has been described as
the fiercest creature on earth and a fearless aggressive fighter that will
drive bears away from their kills. It is, in fact, the wolverine’s reliance
on scavenging in order to survive that has given rise to exaggerations
about its gluttony and ferocity.
The wolverine is also a creature important
in the folklore of North American First Nations peoples and a mammal very
well adapted for its way of life.
Because of its reputation and conflicts
with trappers, the wolverine was considered a pest by European North Americans,
an attitude that persisted into the 1960s. Today, wolverines’ numbers are
greatly reduced in some areas, and conservation biologists and wildlife
managers consider wolverines to be animals in need of protection.
Unique characteristics
Few people, even those who spend a
lot of time outdoors, have seen wolverines in the wild. This contributes
to the animals’ mysterious reputation and explains why they are probably
the most misunderstood and one of the least known of Canada’s wild animals.
Range
The wolverine is found throughout
all northern regions of the globe. Wolverines are not abundant anywhere,
even where they do well. The species is known for a large home range and
low density, which is a measure of its numbers. The Committee on the Status
of Endangered Wildlife in Canada considers wolverines found west of Hudson
Bay to be of “special concern” and the eastern population, found in Quebec
and Labrador, to be “endangered.”
Historically, before the appearance
of Europeans in North America, wolverines occurred throughout Canada and
Alaska, with some small extensions of this range into the western United
States and into the Great Lakes area. They occupied a wide variety of habitat
types, excepting very dry, hot areas.
A portion of the wolverine’s historical
range has been lost. Wolverines have also disappeared from areas with relatively
intact habitats. Eastern Canada and the western United States have been
particularly hard hit. Wolverines disappeared most rapidly at the edges
of their distribution and in Eastern Canada. We do not know if any wolverines
still occur in Eastern Canada, although Labrador and Quebec are still considered
part of the current distribution. Similarly, whether wolverines still occur
on Vancouver Island is unknown.
There are two main reasons why wolverine
populations disappeared from parts of North America. The first is that
wolverines are scavengers—which means they feed on carrion, or dead animals—and
are attracted to bait. Because the wolverines damaged traplines, early
trappers used any means to kill them, including poison. The extensive wolf
poisoning programs that occurred throughout Canada beginning in the late
1700s also killed many wolverines.
The second, and more important, reason
for the decline of wolverine populations is that wolverines have a low
resiliency because of their low densities and low reproduction, or the
number of young that are successfully produced and raised. This means that
wolverine populations have a difficult time rebounding once their numbers
have been lowered by either nature or human-influenced factors.
Feeding
The wolverine is a carnivore, or flesh
eater. It is more of a scavenger than a hunter, and is usually dependent
on other carnivores, such as wolves, to kill the animals for it to eat.
Leftovers from a wolf kill can be considerable. The wolverine has been
known to carry away moose carcasses and caribou heads. Because of its great
dependence on carrion, or dead flesh, from large mammal kills, the wolverine
needs to be able to survive long periods without food. It will revisit
old kills to consume frozen bones and pelts when it cannot find other food.
Some individual wolverines can become
good hunters and can kill young and adult ungulates, or animals with hooves,
such as caribou and even moose, if the prey is in poor physical condition
or if the wolverine has manoeuvred it into a disadvantaged position, such
as in heavy snow.
Since ungulates are not always available,
wolverines must have a diversity of prey in their diet to survive. Female
wolverines with young, or “kits,” rely on small mammals, such as marmots
and ground squirrels. As the movements of family groups are restricted,
food must be found in a smaller area. Snowshoe hares, especially when they
are particularly abundant, are an important food source for all wolverines.
Wolverines hide excess food by burying it or stashing it in rock crevices
or in trees.
Breeding
Wolverines mate in the summer and
reproduce by what is known as “delayed implantation.” The egg is fertilized,
but its development temporarily stops. The egg floats around in the uterus
and implants some time later, as early as November or as late as March.
The active period of gestation, or pregnancy, lasts 30 to 40 days. Birth
occurs between February and May.
The female gives birth to and raises
her kits in a den. Most dens that have been found are in tundra regions
and consist of a complex of snow tunnels that have formed naturally around
rock configurations.
Wolverines can have as many as six
kits, but they typically have three or fewer. Not all of the young survive
their first year: some die of starvation, others from predation. Wolverine
kits grow quickly compared to the young of other mammals. This rapid rate
of growth continues after the mother stops nursing her kits, which happens
at nine or 10 weeks of age. Kits reach the size of adults by seven months
of age.
When food is scarce, a high percentage
of a population will not have young. In fact, some females may not reproduce
even when food is apparently abundant, because raising young results in
a large loss of energy for wolverine mothers. The mechanism of delayed
implantation, which allows wolverines to have young when food is most abundant
and to adjust the size of the litter to the availability of food, is an
effective way of reproducing without sacrificing precious energy.
Conservation
Wolverines have few natural predators,
but they are occasionally attacked and killed, although seldom eaten, by
wolves and other large carnivores. Eagles have been known to take young
kits. Wolverine mothers go to great lengths to find secure dens for their
young, suggesting that predation may be important in some areas. During
the mating season, fights between resident males and other males can occur
as they compete for females. It may be this fighting that encourages the
young males to disperse considerable distances.
Scavenging is a difficult way to survive.
Many young, inexperienced wolverines and very old wolverines die from starvation,
even if food is abundant. Transients, typically young adults passing through
the territory, have a higher mortality rate than residents, because they
do not benefit from hunting in a familiar home range.
The wolverine pelt remains one of
the most prized furs because of its beauty and because frost brushes off
easily. The Inuit and Dene of northern Canada use wolverine fur as trim
and lining for their clothing, such as parkas, mitts, and moccasins. Over
80 percent of all wolverine pelts sold in Canada—about 400 to 600 each
year—come from the Northwest Territories, Nunavut, Yukon, and British Columbia.
Wolverine fur is consistently high in value: a well-handled and prime pelt
sells for an average of $400.
Roads that permit human access to
wolverine habitat can be detrimental to wolverine populations, especially
if the animals are also killed by trapping or hunting. In areas where logging
occurs, wolverines may use the forested corridors adjacent to roads to
get to other parts of their home ranges. This makes them vulnerable to
trappers who use the same roads to set their traps. Major roads, like the
Trans-Canada Highway, can also keep wolverines from reaching important
parts of their habitat.
Denning females are sensitive to disturbance,
particularly human activity. Even the presence of careful researchers has
caused wolverines to abandon their dens. The increasing use of snowmobiles
and skiing in the vicinity of wolverine dens, such as in subalpine mountainous
regions, can harm wolverine populations. However, in tundra areas, female
wolverines have tolerated human activity without abandoning their dens.
A number of zoological organizations
and individuals have been successful in raising wolverines in captivity.
Researchers have learned much about wolverine behaviour from studying these
captive animals. It has been suggested that wolverines raised in captivity
could be used in reintroductions, where wolverines are moved to a new region
in order to increase or augment existing populations or assist in the recovery
of endangered populations. The success of wolverine reintroductions depends
on many factors. There must be a sufficient supply of animals, and reintroduced
animals must originate from the same habitat, environmental conditions,
and genetic stock (to protect those characteristics that have allowed them
to adapt to those environmental conditions) as the animals they are joining.
A recovery plan is being written to
examine the options for the survival of the eastern Canadian wolverine
population and the measures necessary to achieve its recovery. In other
regions of Canada, trapping can be a concern in areas where safe places
or refuges for wolverines need to be maintained, especially if an increase
in population numbers is required. Trapping must be excluded over a very
large area to protect a sufficient number of resident wolverines. Protection
of denning habitat from human disturbance may also be critical for wolverine
survival.
Wolverines are subject to the same
habitat threats that affect other large carnivores in Canada, like the
grizzly bear. The wolverine does not appear to thrive in habitats that
have been permanently altered by land-based activities, such as agriculture,
urban and industrial development, and human settlement. The problem does
not appear to be the actual loss of habitat or the presence of humans.
Instead, the problem seems to be the breaking up, or fragmentation, of
the wolverine habitat, as well as the increased human access to the habitat.
Studies of wolverine ecology do not suggest that wolverines cannot co-exist
with certain land-use activities, such as forestry and mining. However,
where such activities occur, especially if they are coupled with trapping,
low-density wolverine populations can have a difficult time surviving or
growing. Even higher-density populations, such as those in the mountainous
areas of British Columbia, can be negatively affected by human access and
trapping.
The future of the wolverine in Canada
is of international importance. At present, Russia, Canada, and Alaska
maintain the only large and relatively secure populations left in the world.
Within North America, the species’ long-term survival in the western United
States is dependent upon maintaining continuity with wolverines in British
Columbia and Alberta. Success at retaining wilderness in Canada may be
the key to maintaining and restoring the wolverine throughout its range
