Wolverine Figure 1. Gulo gulo in snow. Photo by Gerald and Buff Corsi, California
Academy of Sciences, 1999.
San Francisco State University
Geography 316: Biogeography
The Biogeography of Gulo gulo (wolverine)
by C. Breen, student in Geography 316, Fall 2000
Wolverine Figure 1. Gulo gulo in snow. Photo
by Gerald and Buff Corsi, California
Academy of Sciences, 1999.
Taxonomic Classification of Gulo gulo (Linnaeus, 1758)
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family:
Mustelidae
Subfamily: Mustelinae
Genus: Gulo
Species: Gulo
gulo
(Ewer 1973)
The Wolverine is a tremendous character…. a personality of unmeasured force, courage, and achievement so enveloped in a mist of legend, superstition, idolatry, fear, and hatred, that one scarcely knows how to begin or what to accept as fact. Picture a Weasel—and most of us can do that, for we have met that little demon of destruction, that small atom of insensate courage, that symbol of slaughter, sleeplessness, and tireless, incredible activity—picture that scrap of demoniac fury, multiply that mite some fifty times, and you have the likeness of a Wolverine.
--Ernest Thompson Seton, 1953
Description of Species:
Gulo gulo—also known as wolverine, glutton, skunk bear, Indian devil, and carcajou-- is the largest and least known terrestrial member of the Mustelidae family. Wolverines have thick bushy coats, hairy soles, broad heads, short furry ears, and curved, semi-retractile claws (Figure 1). They are generally a deep, blackish-brown color with a band of pale chestnut beginning on each shoulder and meeting near the tail; the throat and chest often are marked by large white patches (Seton 1953). Seton suggests that the name “skunk bear” is most appropriate because “in size, color, shape, and smell, the wolverine suggests a cross between a skunk and a black bear.” The smell which he (Seton 1953) refers to is produced by anal and ventral gland secretions for marking and defense.
The average length of a wolverine is 36 inches;
their height at the shoulder is, on average, 12 inches (Seton 1974). There is sexual
dimorphism in the animal, with typical females weighing 17-22 pounds and males weighing up
to 45 pounds (Jameson and Peeters 1998). They have a compact, powerful build and
carry the head and tail lower than their arched back. Murray (1987) notes that their
short legs, lumbering gait, and heavy body gives a false impression of clumsiness.
Wolverine have powerful jaws, and their teeth are sharp and strong enough to chew through
bone and frozen carrion (Sleeper 1995). They have 38 teeth with a dental formula of
incisor 3/3, canine1/1, premolar 4/4, and molar 1/2 (Ewer 1973). Apparently their deep
growls and rumbling vocalizations are quite ferocious-sounding. Stuebner
(1997) notes that they are equipped with grizzly bear-like vocal cords that serve as a
defensive bluffing device for scaring away larger predators.
Habitat and Distribution:
The elusive wolverine inhabits tundra, remote mountains, and boreal forests. They generally inhabit areas at or above timberline, oftentimes preferring lower-elevation forests during winter (Thelander 1994). Wolverines occur in such low numbers across most of their remote habitat, and are so mobile, that it is has been extremely difficult to study them (Hornocker and Hash 1980; Primm and Clark 1996). According to Weaver, Pawuet, and Ruggiero (1996) the wolverine is the least studied of the large carnivores. Major information gaps exist in the scientific study of this animal.
Basic information on wolverine habitat relationships is almost non-existent. Ecological factors that may limit wolverine distribution include climate, the availability of relatively undisturbed taiga and tundra, and prey density. According to Primm and Clark (1996), information about wolverine habitat suitability and survival requirements are “thoroughly lacking.” Habitat requirements needs on a landscape scale are currently unknown and may differ substantially between populations (Primm and Clark 1996). Wilson (1982) notes that the wolverine is most at home in regions with snow on the ground throughout winter. They are morphologically well-suited to hunting in the snow and may rely heavily on this advantage during severe winters. Understanding the geographic distribution of the wolverine could provide important insights into wolverine ecology and conservation.
Wolverines have a Holarctic distribution, from Scandinavia through eastern Europe, Russia, and Siberia to Alaska, Canada, and the western United States (Sleeper 1995). While the Mustelidae have a cosmopolitan distribution, Gulo can be found only in the Holarctic region. Prior to the final break between Alaska and Siberia 13,000 to 14,000 years ago, cold-tolerant Gulo gulo moved freely between North America and Eurasia (Cox and Moore 2000). Wolverines are stenotopic animals, extremely sensitive to--and intolerant of--a number of environmental factors (Verts 1998; Hornocker and Hash 1991).
In North America, their historical geographic range extended south from Canada and Alaska , through the montane regions of the West to southern California, Utah, Colorado, and into the Midwest. Their range contracted northward with the advance of European settlement into historically occupied wolverine habitat. Remnant populations are believed to inhabit today only the higher elevation habitats in Idaho, Wyoming and Montana, and possibly Colorado, Minnesota, Washington, Oregon, and California (Sleeper 1995). According to Verts (1998), the critical component of modern day wolverine habitat is the absence of human activity and development. Similarly, Hornocker and Hash (1991) found that wilderness and remote country are essential to wolverine population viability. They also established that the animals prefer ecotones and good cover; the wolverines they studied were extremely reluctant to cross large openings, such as recent clearcuts or burns.
Healthy populations of wolverines appear to exist in Montana and Idaho, but scientist have been unable to locate populations in other plausible mountain locations, such as southwest Colorado or the Cascades of Washington (Stuebner 1997). Hornocker and Hash (1981) state that Montana is the only northwestern state with a viable population. Across their historic range, wolverine numbers are dropping (Wilkinson 1998). Distributional surveys of the wolverine’s historic range are necessary to discover the extent of their current habitat use.
Gulo gulo is increasingly rare in the
southern limits of her habitat due to human disturbance and habitat fragmentation
(Hornocker and Hash, 1980: Thelander 1994; Primm and Clark, 1996). Wolverine numbers
have dipped significantly across their range in the past 100 years due to hunting,
trapping, poisoning, and habitat destruction caused by human settlement, forest clearing,
and mining (Wilkinson 1998). They have evaded trap and camera in California
for over 75 years; wildlife biologist Thomas Kucera acknowledges that “the species
may already be extinct in the state” (Sleeper 1995).
Distribution of Gulo gulo
Wolverine Figure 2. Geographic distribution of Gulo
gulo in Eurasia (1) and North
America (2); the two subspecies are G. g. gulo and G.
g. luscus, respectively
(Pasitschniak-Arts and Lariviere 1995).
Distribution of Mustelidae
Wolverine Figure 3. Intensity of color denotes
preponderance of species
(Murray 1978).
Natural History:
Murray (1987) describes wolverine as
wide-ranging, opportunistic scavenger-predators that feed on carrion, primarily sheep,
caribou, and moose and any small mammals that they can get, including porcupine, squirrel,
beaver, marmot, and rabbit (. When hungry they will dig, climb, and bite their way
through snow, dirt, or wood to get to food, such as a hibernating marmot under ten feet of
snow (Sleeper 1995). Despite her relatively small size, Gulo gulo has
been observed hunting and killing full-sized caribou and deer (Burkholder 1962).
Alaskan wolverines feed on whale, walrus, and seal carcasses. Sleeper (1995) states
that they will also eat eggs, wasp larvae, and berries. In areas with low
concentrations of other scavengers, wolverines often cache their food in snow crevices or
trees for later consumption (Murray 1987). Hunters and trappers have related many
stories of mountain lion, bears, and wolves retreating from their kills at the approach of
wolverine (Seton 1953 and 1974; Jameson and Peeters 1988; Caras 1967). However,
there have been reports of mountain lion, black bears, and wolves attacking and
occasionally killing wolverines, most likely the young and inexperienced (Burkholder 1962;
Hornocker and Hash 1981).
Partial Trophic Web in an Alpine Tundra Community
(G. gulo in lower left corner)
Wolverine Figure 4. Beartooth Plateau in the central
Rocky Mountains. Insectivorous and herbivorous birds are not included (Hoffman 1974).
Gulo gulo is highly mobile and has an extremely large home range, with researchers estimating upper limits of about 390 square kilometers for females and 920 square kilometers for males, including long distance excursions (Banci 1990). Males have considerably larger territories than females, and appear to exclude other males while tolerating females within their range (Murray 1987). Wilson (1982) states that wolverines are most likely polygamous. Hornocker and Hash (1981) believe that food availability is the primary factor determining wolverine range and movement. During spring and summer the home ranges of adult males increases, apparently because of breeding activity. Lactating females have the smallest home ranges (Banci 1990).
Jeff Copeland, a Forest Service biologist, says, “It’s just never ceased to amaze me how far these animals go in a short period of time. The hallmark of the wolverine is probably its insatiable need to be on the move” (Stuebner 1997). Movement of wolverines does not appear to be affected by the presence of rivers, reservoirs, valleys, or major mountain ranges (Hornocker and Hash 1981). They are nonmigratory, do not hibernate in the winter, and often display continuous activity cycles of alternate three to four hour periods of activity and sleep. Inclement weather and/or hunger may lead to extended periods of sleep or activity (Wilson 1982).
To give birth, females build elaborate tunnels and
chambers in secluded high-elevation basins. Nursery dens can often be found in talus
and boulder debris (Sleeper 1995). Like some other mustelids, wolverines experience
delayed implantation of the blastocyst. The advantage this has for the animal is not
known (Murray 1987). The period of active gestation is believed to be from 30 to 40
days. Females bear from one to four blind kits in spring after mating in winter
(Jameson and Peeters 1988). The kits are weaned at about ten weeks, but stay with
their mother for a minimum of six more months (Sleeper 1995). Female
wolverines are reported to breed every other year, at most. This fact,
combined with maternal vulnerability to trapping because of limited foraging range,
may indicate fairly low reproductive rates (Hornocker and Hash 1981). Wolverines are
believed to live about 10 years in the wild and up to 15 years in captivity (Murray
1987). Causes of natural mortality in the wild are not well documented.
Clearly man is the wolverine’s greatest enemy.
Right Side Tracks and Left Hind Foot  |
Skull Views
 |
| Wolverine Figure 5. (Seton 1974; Jackson 1961) | Wolverine Figure 6. Gulo gulo skull, Lyell Canyon, California (Hall and Kelson 1959). |
Evolution:
The fossil history of Gulo gulo is not well
documented. The Mustelidae appear to have originated late in the Eocene from the
ancestral, Holarctic Miacidae family, but the early stages of their evolutionary history
are difficult to trace, mainly because of their forest habitat (Ewer 1973).
Fossilization of forest-dwelling animals is relatively
uncommon. Paleontologists have reconstructed much of Mustelidae history from the
remains of teeth and jaw fragments (Stahl 1985). From these fragments they have
determined that the small, flesh-eating miacids gave rise to most of the modern
families in the order Carnivora (see Figure 7).
Seemingly, it was their more versatile dentition that allowed the early miacids to diversify so successfully (Stahl 1985). Indeed members of the Mustelidae are currently recognized by the loss of their posterior molars; they retain the first and second molars in the mandible and only the first molar in the maxilla (Gittleman 1996). Ewer (1973) notes that Gulo gulo’s subfamily Mustelinae are specialized predators with elongated blade-like carnassials, well developed canines, and short, powerful jaws (Figure 6).
The mustelids remained in the cool forests of the north and diversified from the basic canid stock, which experienced a radiation of its own. Stahl (1985) notes that the mustelids and dogs occupied different niches and the radiation producing their distribution was well under way by Oligocene time. Migration to the southern continents in the early Miocene occurred first in Africa. The immigrations of mustelids out of the Holarctic and into South America happened in the Quaternary (Gittleman 1996). Quaternary mustelid fossils have been found in all habitats from arctic tundra to tropical rainforests (Stahl 1985).
Wolverines are descendents of the
large Miocene and Pliocene Plesiogulo, which apparently derived from a
marten-like ancestor originating from the Martes genus (Gittleman 1989).
Plesiogulo originated in Eurasia and entered North America about seven million years
ago in the Pliocene (Gittleman 1989). The best fossil records for wolverine occur in North
America and Europe and date from about a million years ago (Sleeper 1995). Gulo
gulo of mid-Pleistocene age have been found in cave deposits in Pennsylvania and
Maryland; Holocene fossils have been located in Alaska, Wyoming, Colorado, and Idaho
(Verts 1998). Old and New World wolverines, G. g. gulo and G. g. luscus,
respectively, were formerly considered separate species (Seton 1953; Hall and Kelson
1959). More recent studies have concluded that any division of Gulo into
subspecies is arbitrary (Ewer 1973). Studies of Quaternary deposits indicate evolutionary
progression within the species, with differences in populations being minimal.
Carnivore Evolution
Wolverine Figure 7. Two possible
interpretations of the relationships of
the families of carnivores. Numbers on the left
indicate millions of years
ago (Ewer 1973).
Conservation issues:
Wolverine Figure 8. Drawing of Wolverine by C.G.
Pritchard (Hall and Keson, 1959).
Highly sensitive to human intrusion in their habitat, Gulo
gulo has been called the rarest mammal in North America (Bourne 1997). They are
classified by the International Union for Conservation of Nature and Natural Resources as
“vulnerable” throughout the Holarctic Region (Wilson et al. 2000). In 1995, the
Biodiversity Legal Foundation and Predator Project, two American non-profit groups,
petitioned the U.S. Fish and Wildlife Service (FWS) to list the wolverine as threatened or
endangered in the lower 48. The petition was rejected by FWS because of insufficient
data. Tom Steele, the executive director of the Predator Project describes the
wolverine’s entanglement in a classic catch-22 situation: “We know that they are
in trouble and deserve to be listed under the Endangered Species Act….Unless a
species gets listed, there isn’t any money to do research, but in order to get
listed, you need research to complete an adequate census” (Wilkinson 1998).
Much more needs to be learned about the natural history of this mysterious carnivore in
order to facilitate efforts to save it.
Bibliography
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Bourne, Joel. 1997. “Midsize Carnivores Are Losing Ground.” Defenders 72: 14-20.
Burkholder, Bob L. 1962. “Observations Concerning Wolverine.” Journal of Mammalogy 43 (2): 263-264.
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Jameson, E.W., and Hans J. Peeters. 1988. California Mammals. Berkeley. University of California Press.
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Wolverine Links
Wolverine Photos by Daniel Cox http://www.naturalexposures.com/library/programs/Iax.exe/library/?kw=wolverine&si=0&mi=10
Wolverine Foundation http://www.wolverinefoundation.org/
Predator Conservation http://www.predatorconservation.org/WolverineClear.htm
Canadian Wildlife Service http://www.speciesatrisk.gc.ca/Species/English/SearchDetail.cfm?SpeciesID=172
Wolverine Conservation in Europe http://www.nature.coe.int/CP20/tpvs25e.htm
send comments to bholzman@sfsu.edu
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