Common Name: California Wolverine
Scientific Name: Gulo gulo luteus (Elliot, 1904
Subspecies of Wolverine Gulo gulo (Linnaeus, 1758)
Taxonomic Comments: Not a well-defined subspecies. In the original description, based on only two specimens, Elliot (1904) distinguished this taxon only by noting that it is a "pale species of wolverine, strikingly different...." He stated that the type specimen from Mount Whitney, California, was colored exactly like a specimen from Alaska (subspecies luscus, according to Hall 1981). Not recognized in Wilson and Ruff (1999).
OR/WA BLM and FS Region 6 Units where Suspected or Documented:
Both the Forest Service and BLM have listed the wolverine as a Sensitive Species/Special Status Species in Oregon and Washington.
The California wolverine has been documented or is suspected of occurring on sixteen National Forests in Oregon and Washington (CRG, COL, DES, FWI, GIP, MAL, MBS, MTH, OCH, OKW, RRS, SIU, UMA, UMP, WAW and WIL), two BLM districts in Oregon (BU, PV) and the Spokane BLM district in Washington.
Natural Heritage Program Rank and Status:
Oregon State Rank: S1?; critically imperiled.
Washington State Rank: S1; critically imperiled.
National Rank: N3; vulnerable to extirpation or extinction.
Global Rank: G4T3Q. Not rare; apparently secure globally. Subspecies review for taxonomic listing.
According to the Heritage Program, based on recent years through the mid-1970s the global short-term trend appears to be increasing in California, Oregon, and Washington (see Wilson 1982). However, the long-term trend shows a steady decline in the U.S. beginning in the latter half of the 1800s. The species apparently no longer occurs east of Montana and Wyoming. The last reliable sighting in California was in 1922 (K. Aubrey, cited by Rowland et al. 2003). Wolverines are now very rare or extirpated at the southern periphery of the range in Colorado (Fitzgerald et al. 1994). The species apparently has made a comeback in recent years in Idaho, Montana , and some other western states. Some areas of the U.S. along the continental divide have been recolonized from Canada (Wilson 1982). Hornaker and Hash (1981) asserted stable populations on their study area in Montana, with high dispersal patterns maintaining the stability, rebounding from near extinction in Montana from 1920-1940 (Newby and Wright 1955). In summary, the species has been extirpated from most of range in the contiguous United States, with promising signs of semi-recovery in selected western states.
Figure 1. NatureServe map of the conservation status of the species wolverine (Gulo gulo) in the United States and Canada is shown here for informational purposes. The subspecies Gulo gulo luteus is restricted to the Pacific Coast states and the status for Oregon differs somewhat from what is shown in the map above.
Oregon State Status: LT; listed as threatened species.
Washington State Status: C; candidate for listing; currently under review.
SOC; species of concern; an unofficial status, the species appears to be in jeopardy, but insufficient information to support listing1.
The wolverine is the largest terrestrial species of the “mustelid” or weasel family. It is a somewhat bear-like mustelid with massive limbs and long, thick dark brown fur that is paler on the head. There are two broad lighter brown or yellowish stripes that extend from the shoulder to join on the rump. The wolverine has a bushy tail and relatively large feet for traversing snow. Total length 650-1125 mm; tail length 170-260 mm; hind foot measures 180-192 mm (NatureServe 2007). The wolverine has strong jaws enabling it to feed on frozen carrion and bones. Adults weigh from 17 to 40 pounds (7-32 kg); females average about 10% less than males in linear measurements and 30% less in mass (Hall 1981, Ingles 1965, Nowak 1991).
Differs from the fisher in having yellowish stripes on the sides. Differs from the badger in having darker overall coloration (badger is yellowish gray), yellowish lateral stripes, and longer limbs; lacks the white stripe that in the badger extends from the snout over the top of the head to at least the neck (NatureServe 2007).
The wolverine is one of the rarest and least-known mammals in North America. It occurs at low densities and is secretive and difficult to observe, even in core areas of its range (Aubry et al. 2007). North American wolverines occur primarily in tundra, taiga, and subalpine environments (Ruggiero et al. 2007). The wolverine is one of the least-studied carnivores in North America and its biology remains poorly understood, with many fundamental issues needing additional research. This is particularly true for populations at the southern extent of its range (Ruggiero et al. 2007).
The wolverine is active both day and night but is primarily nocturnal. They tend to occupy higher elevations in summer and lower elevations in winter (Hornocker and Hash 1981, Whitman et al. 1986). They breed April-October, usually in the summer, although this can vary. Implantation is delayed generally until winter. Gestation lasts from seven to nine months; active gestation is from 30-40 days (NatureServe 2007). One to six (usually 2-4) young are born January-April; mainly February or March (reportedly April-June in the Pacific states, Ingles 1965).
Young are weaned beginning at about 7-8 weeks and separate from the mother in the fall. Subadults become independent of their mother at about 9 months of age (Copeland 1996). Individuals become sexually mature generally in the second or third year. Males are sexually mature sometimes as yearlings (Alaska and Yukon); males over three years old were sexually mature in British Columbia. Some females mature at 12-15 months and produce their first litter when two years old (Wilson 1982). In some areas, females may produce litters only every 2-3 years. In British Columbia, most mature females were reproductively active. Lifespan is about 10 years; sometimes 15-18 years (NatureServe 2007, Wilson 1982).
The wolverine is carnivorous but is also an opportunistic feeder. It feeds on a wide variety of roots, berries, small mammals, bird eggs, fledglings, and fish. Wolverine may attack moose, caribou, and deer that are hampered by deep snow. Small and medium size rodents and carrion (especially ungulate carcasses) often make up a large percentage of the diet. They may cache prey in the fork of tree branches or under snow (NatureServe 2007). The wolf and mountain lion are commonly cited as predators of the wolverine
(Copeland et al. 2007).
Wolverines are solitary, wide-ranging animals. Male home ranges are large, up to 1,000 square kilometers (RIC 1999); averaging 422 square kilometers in Montana (Hornocker and Hash 1981) and 535 square kilometers in Alaska (Whitman et al. 1986). Home ranges of females with young are much smaller, ranging from 73 to 416 square kilometers (Hornocker and Hash 1981, Gardner 1985, Magoun 1985, Whitman et al. 1986, Banci 1987, Copeland 1996). Subadults remain associated with their natal area until sexual maturity at about 2 years of age (Copeland 1996). Available evidence indicates that juveniles disperse around 30-100 km from their natal range, although dispersal movements of more than 300 km are known (Magoun 1985, Gardner et al. 1986). Mountain ranges and large rivers are not barriers to the same extent that they are for many related species (Hornocker and Hash 1981, Banci 1987).
In some areas males appear to be territorial, but in Montana there was extensive overlap of the ranges of both the same and opposite sexes. Apparently territory/range size depends on availability of denning sites and food supply (see Wilson 1982). Some individuals travel regularly over the same route (Wilson 1982).
Range, Distribution, and Abundance:
This subspecies of wolverine is found in California, Oregon, Washington, and part of southern British Columbia (Hall 1981). (However, subspecies status, specifically whether there are subspecies of this animal, is in question). In California, it historically ranged from Del Norte and Trinity counties eastward through Siskiyou and Shasta counties, and southward through the Sierra Nevada to Tulare County (Schempf and White 1977); elevational range 1600-14,200 ft, mean of 143 sightings about 8000 ft (California DF&G 1990). In the southern Sierra Nevada, range includes high elevation facilities associated with Eastside Hydro at Bishop Creek and Rush Creek and Westside Hydro at Kaweah (Biosystems Analysis 1989). In Oregon, it is recorded in the Cascade Mountains from Mount Hood, McKenzie Valley, near Three Fingered Jack Mountain, and Steen's Mountain in Harney County (see Wilson 1982). It is also recorded from the Cascade Mountains in Washington (see Johnson (1977) for a review and maps of all twentieth-century records through the mid-1970s).
Figure 2. The current estimated range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. Data provided by NatureServe in collaboration with Bruce Patterson, Wes Sechrest, Marcelo Tognelli, Gerardo Ceballos, The Nature Conservancy-Migratory Bird Program, Conservation International-CABS, World Wildlife Fund-US, and Environment Canada-WILDSPACE.
Since the 1800s, dramatic contractions have occurred within the historical range of the wolverine in the contiguous United States (Ruggiero et al. 2007). Aubry et al. (2007) discusses that by the mid-1900s, evidence of wolverine occurrence in the contiguous United States had become so scarce that many believed it had been extirpated from most or all of its former range (e.g., Wright and Thompson 1935, Grinnell et al. 1937, Allen 1942, Newby and Wright 1955). Results from Aubry (2007) suggest that the wolverine may have experienced significant population declines or local extirpations in the Cascade Range and northern Rocky Mountains during the early 1900s, as previous authors have speculated (Wright and Thompson 1935, Newby and Wright 1955, Newby and McDougal 1964). However, numerous wolverine records in the contiguous United States dating from the 1960s and 1970s suggested that the wolverine was reclaiming portions of its former range during that time (Nowak 1973, Yocom 1974, Johnson 1977).
Figure 3. Historical Wolverine Records in the Contiguous United States—1801 to 1960. Aubry et al. 2007.
Wolverine2 distribution in the contiguous United States appears to be closely related to habitat conditions that become increasingly fragmented in more southerly regions. Consequently, there is a much greater potential for wolverine populations in the contiguous United States to become isolated than has been recognized previously (Aubry et al. 2007). Nuclear and mitochondrial DNA data (Schwartz et al. 2007) indicate the wolverine has been isolated for a substantial period of time, consistent with the hypothesis of Aubry et al. (2007) regarding the disjunct nature of the wolverine's range in the mountains of the Pacific Coast. This is also consistent with Grinnell et al. (1937), as they found little evidence that wolverines historically occurred north of the central Sierra Nevada (Schwartz et al. 2007).
Many wolverine populations appear to be relatively small and isolated. Even in “high-quality” habitat, wolverines exist at low densities (Ruggiero et al. 2007).
Outside of Alaska, Montana and Idaho likely have the largest populations in the United States (perhaps a few hundred individuals in each state) (NatureServe 2007). Acknowledging a lack of substantial data, Predator Conservation Alliance (2001) stated that extrapolation of the best available information indicates an estimated population of fewer than 750 wolverines in the contiguous United States, including an estimated 400-600 in the U.S. northern Rocky Mountains, and perhaps 100 across the Northwest and Sierra Nevada. They may occur at relatively low population densities, as low as one wolverine per 65 sq km in Montana (Hornocker and Hash 1981).
Figure 4. Recent (a) and current (b) wolverine records in the contiguous United States—1961 to 1994. (Aubry et al. 2007).
As per Aubry et al. (2007), between 1921 and 1950, there is only 1 wolverine record from Washington, 1 from Oregon, 5 from Idaho, 13 from Montana, and 1 from Wyoming. The most recent verifiable record of wolverine occurrence in California dates from 1922. However, records from these states in subsequent years were relatively numerous, suggesting that wolverines may have become reestablished in northwestern regions after a period of range-wide decline.
During the 1960s and 1970s, wolverines began appearing in low-elevation, non-forested habitats in eastern Washington and Oregon (Fig. 4a). However, there is no evidence of wolverine occurrence in eastern Washington or Oregon currently (Fig. 4b). It is unclear why wolverines began appearing in previously unoccupied areas during this time period, but Aubry et al. (2007) agrees with Verts and Carraway (1998) that these records probably represent extreme dispersal events that were not representative of self-sustaining populations.
The wolverine is found chiefly in subalpine and alpine forests (Ingles 1965); also alpine meadows, forests of lodgepole pine and red fir (Biosystems Analysis 1989).
Figure 5. Historical wolverine records from the western United States on Holdridge climatic life zones (figure from Aubry et al. 2007).
Fallen logs and debris are important habitat components. The wolverine dens in caves, rock crevices, under fallen trees or tree roots, in thickets, or similar sites (NatureServe 2007). It is generally found in areas remote from humans and human development, the habitat conditions that influence its distribution and abundance are largely unknown (Banci 1994).
Figure 6. Historical wolverine records from the western United States on selected Kuchler potential natural vegetation types (figure from Aubry et al. 2007).
As stated in Copeland et al. (2007), Wright et al. (1932) characterized the wolverine as “being restricted to the higher life zones” and recommended protection and “enlargement of park areas in the upper Canadian and Hudsonian zones” to ensure wolverine persistence. This Hudsonian life zone signature may define a niche that is limited to high-elevation mountain ranges in the conterminous United States that is critical to wolverine persistence.
In the western mountains, historical wolverine records generally occurred in or near alpine vegetation (Aubry et al. 2007). Wolverines favored high elevations in nearly all of Copeland et al. (2007) models; 83% of all wolverine use points occurred in the 2200 – 2600 meter elevation zone. This preference was not restricted to either summer or winter. Although a seasonal shift in elevational use occurred, it was relatively minor. Wolverines moved from high-elevation whitebark communities in summer to mid-elevation Douglas-fir and lodgepole pine in winter (Copeland et al. 2007). It is suggested by Magoun and Copeland (1998) that high elevations provide deep and persistent snow cover necessary for the presence and maintenance of late winter reproductive dens. Aubry et al. (2007) investigated potential relations between wolverines and alpine vegetation, cold temperatures, and spring snow cover during the latter portion of the wolverine denning period (15 Apr–14 May). The only habitat layer that fully accounted for historical distribution patterns was spring snow cover.
Figure 5. All areas in the Pacific Coast and Rocky Mountains with numerous wolverine records, including areas that generally lacked alpine vegetation or climatic conditions (e.g., northern ID, northwestern MT, and northern UT; Figs. 3, 4) had >25% probability of spring snow cover, and most had >50% probability (figure from Aubry et al. 2007).
Snow cover that persists through the spring denning period appears vital to reproduction. Elevations and habitats associated with this attribute may be critical for successful natal (birthing) dens throughout the wolverine's range (Ruggiero et al. 2007). Understanding the ecological and environmental characteristics of wolverine natal dens in North America is based on descriptions of 15 dens established by only five females – three in Alaska and two in Idaho (Magoun and Copeland 1998).
It appears that wolverines, at least in the Pacific Coast mountains, are associated with relatively large expanses of alpine habitat conditions and snow cover that persists through the spring denning season (Schwartz et al. 2007). Although these findings have range-wide implications, they may be most relevant in peripheral portions of the wolverine's range where increasing temperatures associated with global climate change could shift treeline to higher elevations, in effect shrinking the alpine zone (Millar et al. 2004) and decreasing the probability of spring snow cover. If such changes occur, current wolverine habitat at the periphery of the range may lose the ability to support viable populations of wolverines (Schwartz et al. 2007).
Wolverine may be impacted by management practices that influence subalpine and alpine communities, particularly those that reduce the presence and opportunity for carrion availability (Copeland et al. 2007).
Resource extraction (including timber harvesting), backcountry skiing and snowmobiling, roads, and other forms of human disturbance can impact wolverine (Ruggiero et al. 2007). Researchers in British Columbia found a consistent negative association between wolverine occurrence and areas where helicopter and backcountry skiing occur. However, the causal factors associated with these patterns are not well understood (see Copeland et al. 2007, Krebs et al. 2007).
Trapping has been the primary source of wolverine mortality in North America (Predator Conservation Alliance 2001). Wolverines are managed as a commercial furbearer species in British Columbia (Hatler 1989), and they have been harvested commercially for nearly two centuries (Novak et al. 1987). Wolverine populations have limited growth capability and are sensitive to overharvest. Because current provincial wolverine harvest is within overall sustainable limits, harvest management changes are likely not warranted. Wolverine populations in British Columbia are contiguous to those in adjacent jurisdictions of Canada and the United States. Management of wolverines in British Columbia will likely influence wolverine populations in those jurisdictions and vice versa (Lofroth and Ott 2007).
High road densities, timber sales, or housing developments on the fringes of subalpine habitats may reduce potential for winter foraging and kit rearing, and increase the probability of human-caused wolverine mortality.
Management programs bearer likely most effective when covering a regional, rather than local scale, for this wide-ranging, low-density species. Maintaining wilderness and roadless areas is critical (NatureServe 2007).
Protection of natal denning habitat from human disturbance may be critical. Montane coniferous forests, suitable for winter foraging and summer kit rearing, may only be useful if connected with subalpine cirque habitats required for natal denning, security areas, and summer foraging. In addition, these habitats must be available during the proper season. Subalpine cirque areas, important for natal denning, may be made unavailable by winter recreational activities (www.wolverinefoundation.org).
These environments become increasingly fragmented at southern latitudes, where wolverine populations occur at low densities and are potentially vulnerable to human-caused mortality (Ruggiero et al. 2007). High levels of genetic structure observed in both current and historical populations indicate that dispersal between mountain ranges is limited. Where populations are fragmented, persistence is critically dependent on dispersal between habitat islands (Ruggiero et al. 2007).
Although available data indicate that the habitat conditions required for wolverine dens play an important role in limiting their distribution and abundance, the understanding of habitat requirements continues to be extrapolated from a limited data set. Additional field studies are urgently needed to fill these and other critical information gaps, including the potential effects of global warming (Ruggiero et al. 2007).
Because alpine conditions become increasingly fragmented at southern latitudes, opportunities for population recovery and natural recolonization will be limited in these areas (Ruggiero et al. 2007). Given current predictions about warming climates, this situation will likely be exacerbated (see Aubry et al. 2007, Copeland et al. 2007, Schwartz et al. 2007).
Given the fragmented nature of suitable habitat conditions for the wolverine at the southern extent of its historical range in North America and extensive urban and agricultural development in intervening areas, the reestablishment of southern wolverine populations seems unlikely to occur without human intervention (Aubry et al. 2007). Because southern wolverine populations appear to have been extirpated by human-caused mortality factors that no longer pose a significant threat, reintroduction may be an appropriate management strategy. However, the potential effects of increased human activities and disturbance on the reestablishment and persistence of wolverine populations should receive careful consideration during reintroduction planning (Aubry et al. 2007).
Because wolverine are highly susceptible to the effects of human disturbance, protecting areas to reduce or mitigate disturbance can be effective management tools. Options to consider include restricting access to areas utilized by wolverine. Roads and trails that provide vehicle access and snowmobiles and skiing that provide cross-country access all contribute to potential disturbance within wolverine habitat. In certain areas it may be appropriate to seasonally restrict this type of access in order to protect the species.
Ski area development or expansion is another potential impact to wolverine, resulting in loss of habitat and an increase in disturbance to the species. Any proposed areas should be carefully assessed for their impacts. Potential development should be situated in areas less likely to be used by wolverine. Areas of suitable denning habitat should be protected from development.
As with activities associated with recreation, management actions such as timber harvest also have the potential to impact wolverine by reducing habitat and increasing disturbance. Areas proposed for harvest should also be carefully assessed for impacts. Seasonally restricting harvest activity may be appropriate.
Other pertinent information (references to Survey Protocols, etc):
Rowland et al. (2003) evaluated performance of landscape models for wolverines within their historical range at 2 scales based on recent observations (n = 421) from Washington, Oregon, Idaho, and Montana. At the subbasin scale, simple overlays of habitat and road-density classes were effective in predicting observations of wolverines. At the watershed scale, they used a Bayesian belief network model to provide spatially explicit estimates of relative habitat capability.
The model had three inputs: amount of habitat, human population density, and road density. At both scales, the best models revealed strong correspondence between means of predicted counts of wolverines and means of observed counts. Their results can be used to guide regional conservation planning for wolverines.
Appendix 1. Wolverine Photos (Copyright C. Long, The Wolverine Foundation, Inc.
Appendix 2. Wolverine Distribution Information. Aubry et al. (2007).
Appendix 3. Keystone Conservation (formerly Predator Conservation Alliance) Management Recommendations.
Theresa Stone, Umpqua National Forest, Roseburg OR
26 September 2007
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Appendix 1. Wolverine Photos (Copyright C. Long, The Wolverine Foundation, Inc.
Appendix 2. Wolverine Distribution Information; Aubry et al. (2007).
Re: your comment – maybe Pacific Coast states would be more appropriate?
Historical Wolverine Records in the Contiguous United States—1801 to 1960
Pacific Coast mountains. We found many historical records of wolverine occurrence in the Pacific Coast mountains located almost entirely in Washington (29 records; 4 verifiable) and California (58 records; 10 verifiable); we found 2 documented records in Oregon. We mapped 24 records in north-central Washington, 2 in north-central Oregon, and 36 in central California (Fig. 3). Our findings indicate that the wolverine's historical range was discontinuous in the Pacific states. The holotype specimen of the southern wolverine (Gulo gulo luteus) was collected in California in 1903 (Elliot 1903).
Recent Wolverine Records in the Contiguous United States—1961 to 1994
Pacific Coast mountains: We found 23 recent records of wolverine occurrence in the Pacific states, including 17 in Washington (11 verifiable) and 6 in Oregon (5 verifiable); we found none in California. We mapped all records in both states, including many records located in physiographic provinces that lacked historical records, such as the high plateaus of northeastern Washington, the Columbia River Basin in both states, and the basin and range areas of southeastern Oregon (Fig. 4a).
Current Wolverine Records in the Contiguous United States—1995 to 2005
The distribution of current wolverine records in the contiguous United States is limited to north-central Washington, northern and central Idaho, western Montana, and northwestern Wyoming (Fig. 4b). The most likely explanation for this apparent range loss involves human activities. There is a long history of mining and high-elevation sheep grazing during spring and summer (Fritz 1941, McKelvey and Johnston 1992), and commercial trapping of American marten (Martes americana) and other boreal furbearers during winter (Coman 1912, Grinnell et al. 1937, Melchior et al. 1987). Each of these activities would have increased the likelihood of human encounters with wolverines.
Pacific Coast mountains: We mapped 7 verifiable records of wolverine occurrence in northern Washington (Fig. 4b). We found no current records in Oregon or California, despite concerted efforts to obtain verifiable evidence of wolverine occurrence using remote cameras, bait stations, and helicopter surveys in many areas of the Pacific states (Kucera and Barrett 1993; Aubry and Lewis 2003; Zielinski et al. 2005; K. B. Aubry, unpublished data).
Appendix 3. Keystone Conservation (formerly Predator Conservation Alliance)
Predator Conservation Alliance's Literature Summary
Draft - January 24, 2001 - Draft
Conservation Status and Needs of the Wolverine (Gulo gulo)
(used by permission)
Science-based policies needed to protect and restore the wolverine and its habitat
throughout the U.S. lower 48 states
A. Forest practices, access, and recreation
1. Maintain forested areas largely free of human disturbance
a. Identify priority habitat for wolverines
b. Protect suitable habitat from human disturbance
i. Maintain unroaded areas and restore roaded areas by maintaining
road densities at no greater than one mile of road per square mile of habitat.
ii. Limit clearcut logging within priority wolverine habitat.
iii. Roads used to access logging operations and other developments should be closed and obliterated, including snowmobile use in winter.
iv. Mining activity, developed campgrounds, and other permanent
developments should be prohibited from priority wolverine habitat, because the associated human activity is likely to displace wolverines from the area.
2. Protect wolverine denning habitat from human disturbance
a. Identify suitable denning habitat
b. Protect suitable denning habitat from snowmobiles, helicopter skiing, and other forms of intensive human use, especially during denning season (February through May)
3. Maintain and restore quality habitat for ungulates and other prey within wolverine habitat.
1. Trapping has been the primary source of wolverine mortality in North America.
2. Trapping for wolverines should be prohibited from all areas where the practice is not known to be sustainable and compatible with maintaining healthy and robust wolverine populations.
3. Incidental take - wolverines killed in traps set for other species - is a significant threat to the wolverine, and thus all trapping that may pose a risk to wolverines should be prohibited within priority wolverine habitat.
C. Connectivity vs. Fragmentation
1. Because of their wide ranges and low population densities, wolverine conservation and management requires a regional perspective. Priority habitats for subpopulations should be identified and protected, as well as areas of connection between these sub-populations, across the entire western United States and Canada.
2. Highways threaten wolverines due to direct mortality and especially because they may pose a barrier to movement, thereby isolating wolverine populations and areas of suitable habitat across the Rocky Mountains of the U.S. and Canada.