Federal Register: December 14, 2010 (Volume 75, Number 239)
DOCID: fr14de10-19 FR Doc 2010-30573
DEPARTMENT OF THE INTERIOR
Veterans Affairs Department
CFR Citation: 50 CFR Part 17
Docket ID: [Docket No. FWS-R6-ES-2008-0029; MO 92210-0-0008-B2]
NOTICE: Part III
DOCUMENT ACTION: Notice of 12-month petition finding.
Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the North American Wolverine as Endangered or Threatened
DATES: This finding was made on December 14, 2010.
We, the U.S. Fish and Wildlife Service (Service), announce a 12month finding on a petition to list the North American wolverine (Gulo gulo luscus) as an endangered or threatened species under the Endangered Species Act of 1973, as amended (Act). After review of all available scientific and commercial information, we find that the North American wolverine occurring in the contiguous United States is a distinct population segment (DPS) and that addition of this DPS to the Lists of Endangered and Threatened Wildlife and Plants is warranted. Currently, however, listing the contiguous U.S. DPS of the North American wolverine is precluded by higher priority actions to amend the Lists of Endangered and Threatened Wildlife and Plants. Upon publication of this 12month petition finding, we will add the contiguous U.S. DPS of the wolverine to our candidate species list. We consider the current range of the species to include portions of the States of Washington, Idaho, Montana, Wyoming, Colorado, Utah, Oregon, and California. However, due to the dispersal abilities of individual wolverines, we expect that wolverines are likely to travel outside the currently occupied area. We will develop a proposed rule to list this DPS as our priorities allow (see section on Preclusion and Expeditious Progress). We will make any determination on critical habitat during development of the proposed listing rule. In the interim, we will address the status of this DPS through our annual Candidate Notice of Review.
Interior Department, Fish and Wildlife Service
Section 4(b)(3)(B) of the Act (16 U.S.C. 1531 et seq.) requires that, for any petition to revise the Federal Lists of Endangered and Threatened Wildlife and Plants that contains substantial scientific and commercial information that listing a species may be warranted, we make a finding within 12 months of the date of receipt of the petition. In this finding, we determine whether the petitioned action is: (a) Not warranted, (b) warranted, or (c) warranted, but the immediate proposal of a regulation implementing the petitioned action is precluded by other pending proposals to determine whether species are threatened or endangered, and whether expeditious progress is being made to add or remove qualified species from the Federal Lists of Endangered and Threatened Wildlife and Plants. Section 4(b)(3)(C) of the Act requires that we treat a petition for which the requested action is found to be warranted but precluded as though resubmitted on the date of such finding, that is, requiring a subsequent finding to be made within 12 months. We must publish these 12month findings in the Federal Register.
Previous Federal Actions
On April 19, 1995, we published a finding (60 FR 19567) that a previous petition, submitted by the Predator Project (now named the Predator Conservation Alliance) and Biodiversity Legal Foundation to list the wolverine in the contiguous United States, did not provide substantial information indicating that listing the wolverine in the contiguous United States may be warranted.
On July 14, 2000, we received a petition dated July 11, 2000, submitted by the Biodiversity Legal Foundation, Predator Conservation Alliance, Defenders of Wildlife, Northwest Ecosystem Alliance, Friends of the Clearwater, and Superior Wilderness Action Network, to list the wolverine within the contiguous United States as a threatened or endangered species and designate critical habitat for the species.
On October 21, 2003, we published a 90day finding that a petition to list the wolverine in the contiguous United States failed to present substantial scientific and commercial information indicating that listing may be warranted (68 FR 60112).
On September 29, 2006, as a result of a complaint filed by Defenders of Wildlife and others alleging we used the wrong standards to assess the wolverine petition, the U.S. District Court, Montana District, ruled that our 90day petition finding was in error and ordered us to make a 12month finding for the wolverine. On April 6, 2007, a deadline for this 12month finding was extended to February 28, 2008.
On March 11, 2008, we published a 12month finding of ``not warranted'' for the wolverine in the contiguous United States (73 FR 12929). In that finding we determined that the wolverine in the contiguous United States did not constitute a distinct population segment or a significant portion of the range of wolverines in North America and so was not eligible for listing under the Act.
On July 8, 2008 we received a Notice of Intent to Sue from Earthjustice alleging violations of the Act in our March 11, 2008, 12 month finding. On September 30, 2008, Earthjustice filed a complaint in the U.S. District Court, District of Montana, seeking to set aside and remand the 12month finding back to the Service for reconsideration.
On March 6, 2009, the Service agreed to settle the case with Earthjustice by voluntarily remanding the 12month finding and issuing a new 12month finding by December 1, 2010. Following the settlement agreement, the court dismissed the case on June 15, 2009, and ordered the Service to comply with the settlement agreement.
On April 15, 2010, the Service published a Notice of Initiation of
a 12month finding for wolverines in the contiguous United States (75 FR 19591).
Taxonomy and Life History
The wolverine has a holarctic distribution including northern
portions of Europe, Asia, and North America. The currently accepted
taxonomy classifies wolverines worldwide as a single species, Gulo
gulo. Old and New World wolverines are divided into separate subspecies. Wolverines in the
contiguous United States are a part of the New World subspecies, G. g. luscus: the North American wolverine (Kurten and Rausch 1959 p. 19; PasitschniakArts and Lariviere 1995, p. 1). The species is known by several common names including mountain devil, glutton, caracajou, quickhatch, gulon, skunk bear, as well as wolverine.
The wolverine is the largest terrestrial member of the family Mustelidae. Adult males weigh 12 to 18 kilograms (kg) (26 to 40 pounds (lb), and adult females weigh 8 to 12 kg (17 to 26 lb) (Banci 1994, p. 99). The wolverine resembles a small bear with a bushy tail. It has a broad, rounded head; short, rounded ears, and small eyes. Each foot has five toes with curved, semiretractile claws used for digging and climbing (Banci 1994, p. 99).
A large number of female wolverines (40 percent) are capable of giving birth at 2 years old, become pregnant most years, and produce litter sizes of approximately 3.4 kits on average. Pregnant females commonly resorb or spontaneously abort litters prior to giving birth (Magoun 1985, pp. 3031; Copeland 1996, p. 43; Persson et al. 2006, p. 77; Inman et al. 2007c, p. 70). It is likely that, despite the high rate of initiation of pregnancy, due to the spontaneous abortion of litters resulting from resource limitation, actual rates of successful reproduction in wolverines are among the lowest known for mammals (Persson 2005, p. 1456). In one study of knownaged females, none reproduced at age 2, 3 of 10 first reproduced at age 3, and 2 did not reproduce until age 4; the average age at first reproduction was 3.4 years (Persson et al. 2006, pp. 7677). The average age at first reproduction is likely more than 3 years (Inman et al. 2007c, p. 70).
It is common for females to forgo reproducing every year, possibly saving resources to increase reproductive success in subsequent years (Persson 2005, p. 1456). Supplemental feeding of females increases reproductive potential (Persson 2005, p. 1456). Foodsupplemented females were also more successful at raising kits to the time of weaning, suggesting that wolverine reproduction and ultimately population growth rates and viability are foodlimited. By age 3, nearly all female wolverines become pregnant every year, but energetic constraints due to low food availability result in loss of pregnancy in about half of them each year. It is likely that, in many places in the range of wolverines, it takes 2 years of foraging for a female to store enough energy to successfully reproduce (Persson 2005, p. 1456).
Breeding generally occurs from late spring to early fall (Magoun and Valkenburg 1983, p. 175; Mead et al. 1991, pp. 808811). Females undergo delayed implantation until the following winter to spring, when active gestation lasts from 30 to 40 days (Rausch and Pearson 1972, pp. 254257). Litters are born from midFebruary through March, containing one to five kits, with an average in North America of between 1 and 2 kits (Magoun 1985, pp. 2831; Copeland 1996, p. 36; Krebs and Lewis 1999, p. 698; Copeland and Yates 2006, pp. 3236; Inman et al. 2007c, p. 68).
Female wolverines use natal (birthing) dens that are excavated in snow. Persistent, stable snow greater than 1.5 meters (m) (5 feet (ft)) deep appears to be a requirement for natal denning, because it provides security for offspring and buffers cold winter temperatures (Pulliainen 1968, p. 342; Copeland 1996, pp. 9297; Magoun and Copeland 1998, pp. 13171318; Banci 1994, pp. 109110; Inman et al. 2007c, pp. 7172; Copeland et al. 2010, pp. 240242). Female wolverines go to great lengths to find secure den sites, suggesting that predation is a concern (Banci 1994, p. 107). Natal dens consist of tunnels that contain wellused runways and bed sites and may naturally incorporate shrubs, rocks, and downed logs as part of their structure (Magoun and Copeland 1998, pp. 13151316; Inman et al. 2007c, pp. 7172). In Idaho, natal den sites occur above 2,500 m (8,200 ft) on rocky sites, such as northfacing boulder talus or subalpine cirques in forest openings (Magoun and Copeland 1994, pp. 13151316). In Montana, natal dens occur above 2,400 m (7,874 ft) and are located on north aspects in avalanche debris, typically in alpine habitats near timberline (Inman et al. 2007c, pp. 7172). Offspring are born from midFebruary through March, and the dens are typically used through late April or early May (Myrberget 1968, p. 115; Magoun and Copeland 1998, pp. 13141317; Inman et al. 2007b, pp. 5559). Occupation of natal dens is variable, ranging from approximately 9 to 65 days (Magoun and Copeland 1998, pp. 1316 1317).
Females may move kits to multiple secondary (maternal) dens as they grow during the month of May (Pulliainen 1968, p. 343; Myrberget 1968, p. 115), although use of maternal dens may be minimal (Inman et al. 2007c, p. 69). Timing of den abandonment is related to accumulation of water in dens (due to snow melt), the maturation of offspring, disturbance, and geographic location (Myrberget 1968, p. 115; Magoun 1985, p. 73). After using natal and maternal dens, wolverines may also use rendezvous sites through early July. These sites are characterized by natural (unexcavated) cavities formed by large boulders, downed logs (avalanche debris), and snow (Inman et al. 2007c, p. 5556). Habitat, Space, and Food
In North America, wolverines occur within a wide variety of alpine, boreal, and arctic habitats, including boreal forests, tundra, and western mountains throughout Alaska and Canada. The southern portion of the species' range extends into the contiguous United States, including highelevation alpine portions of Washington, Idaho, Montana, Wyoming, California, and Colorado (Wilson 1982, p. 644; Hash 1987, p. 576; Banci 1994, p. 102, PasitschniakArts and Lariviere 1995, p. 499; Aubry et al. 2007, p. 2152; Moriarty et al. 2009, entire; Inman et al. 2009, pp. 2225). Wolverines do not appear to specialize on specific vegetation or geological habitat aspects, but instead select areas that are cold and receive enough winter precipitation to reliably maintain deep persistent snow late into the warm season (Copeland et al. 2010, entire). The requirement of cold, snowy conditions means that, in the southern portion of the species' range where ambient temperatures are warmest, wolverine distribution is restricted to high elevations, while at more northerly latitudes, wolverines are present at lower elevations and even at sea level in the far north (Copeland et al. 2010, Figure 1).
In the contiguous United States, wolverines likely exist as a
metapopulation (Aubry et al. 2007, p. 2147, Figures 1, 3). A
metapopulation is a network of semiisolated populations, each
occupying a suitable patch of habitat in a landscape of otherwise
unsuitable habitat (Pulliam and Dunning 1997, pp. 212214).
Metapopulations require some level of regular or intermittent migration
and gene flow among subpopulations, in which individual populations
support oneanother by providing genetic and demographic enrichment
through mutual exchange of individuals (Meffe and Carroll 1997, p.
678). Individual subpopulations may go extinct or lose genetic
viability, but are then ``rescued'' by immigration from other
subpopulations, thus ensuring the persistence of the metapopulation as
a whole. Metapopulation dynamics (the process of extinction and
recolonization by subpopulations) rely on the ability of subpopulations
to support one another through exchange of individuals for genetic and demographic enrichment. If
metapopulation dynamics break down, either due to changes within subpopulations or loss of connectivity, then the entire metapopulation may be jeopardized due to subpopulations becoming unable to persist in the face of inbreeding or demographic and environmental stochasticity (Pulliam and Dunning 1997b, pp. 221222). We believe this outcome is likely for wolverine, due to their naturally low reproductive rates and low densities.
Wolverines are opportunistic feeders and consume a variety of foods depending on availability. They primarily scavenge carrion, but also prey on small animals and birds, and eat fruits, berries, and insects (Hornocker and Hash 1981, p. 1290; Hash 1987, p. 579; Banci 1994, pp. 111113). Wolverines have an excellent sense of smell that enables them to find food beneath deep snow (Hornocker and Hash 1981, p. 1297).
Wolverines require a lot of space; the availability and distribution of food is likely the primary factor in determining wolverine movements and home range size (Hornocker and Hash 1981, p. 1298; Banci 1994, pp. 117118). Female wolverines forage close to den sites in early summer, progressively ranging further from dens as kits become more independent (May et al. 2010, p. 941). Wolverines travel long distances over rough terrain and deep snow, and adult males generally cover greater distances than females (Hornocker and Hash 1981, p. 1298; Banci 1994, pp. 117118; Moriarty et al. 2009, entire; Inman et al. 2009, pp. 2228; Brian 2010, p. 3; Copeland and Yates 2006, Figure 9). Home ranges of wolverines are large, and vary greatly in size depending on availability of food, gender and age of the animal, and differences in habitat quality. Home ranges of adult wolverines also vary in size depending on geographic location. Home ranges in Alaska were approximately 100 square kilometers (km\2\) to over 900 km\2\ (38.5 square miles (mi\2\) to 348 mi\2\) (Banci 1994, p. 117). Average home ranges of resident adult females in central Idaho were 384 km\2\ (148 mi\2\), and average home ranges of resident adult males were 1,522 km\2\ (588 mi\2\) (Copeland 1996, p. 50). Wolverines in Glacier National Park had average adult male home ranges of 496 km\2\ (193 mi\2\) and adult female home ranges of 141 km\2\ (55 mi\2\) (Copeland and Yates 2006, p. 25). Wolverines in the Greater Yellowstone Ecosystem had average adult male home ranges of 797 km\2\ (311 mi\2\), and average adult female home ranges of 329 km\2\ (128 mi\2\) (Inman et al. 2007a, p. 4). These home range sizes are large relative to the body size of wolverines, and may indicate that wolverines occupy a relatively unproductive niche in which they must forage over large areas to consume the amount of calories needed to meet their life history requirements (Inman et al. 2007a, p. 11).
Wolverines naturally occur in low densities of about 1 wolverine per 150 km\2\ (58 mi\2\) with a reported range from 1 per 65 to 337 km\2\ (25 to 130 mi\2\) (Hornocker and Hash 1981, pp. 12921295; Hash 1987, p. 578; Copeland 1996, pp. 3132; Copeland and Yates 2006, p. 27; Inman et al. 2007a, p. 10; Squires et al. 2007, p. 2218). No systematic population census exists over the entire current range of wolverines in the contiguous United States, so the current population level and trends remain unknown. However, based on our current knowledge of occupied wolverine habitat and wolverine densities in this habitat, it is reasonable to estimate that the wolverine population in the contiguous United States numbers approximately 250 to 300 individuals (Inman 2010b, pers. comm.). The bulk of the current population occurs in the northern Rocky Mountains with a few individuals in the North Cascades and one known individual each in the Sierra Nevada and southern Rocky Mountains. Within the area known to currently have wolverine populations relatively few wolverines can coexist due to their naturally low population densities, even if all areas were occupied at or near carrying capacity. Given the natural limitations on wolverine population density, it is likely that historic wolverine population numbers were also low (Inman et al. 2007a, Table 6). Because of these natural limitations, we believe that densities and population levels in the northern Rocky Mountains and North Cascades where populations currently exist are likely not substantially lower than population densities were in these areas prior to European settlement. However, historically, the contiguous U.S. population would have been larger than it is today due to the larger area occupied by populations when the southern Rocky Mountains and Sierra Nevada were occupied at full capacity.
Wolverine Status in Canada and Alaska
The bulk of the range of North American wolverines is found in Canada and Alaska. Wolverines inhabit alpine tundra, boreal forest, and arctic habitats in Canada and Alaska (Slough 2007, p. 78). Wolverines in Canada have been divided into two populations for management by the Canadian Government: An eastern population in Labrador and Quebec, and a western population that extends from Ontario to the Pacific coast, and north to the Arctic Ocean. The eastern population is currently listed as endangered under the Species At Risk Act in Canada, and the western population is designated as a species of special concern (COSEWIC 2003, p. 8).
The current status of wolverines in eastern Canada is uncertain. Wolverines have not been confirmed to occur in Quebec since 1978 (Fortin et al. 2005, p. 4). Historical evidence of wolverine presence in eastern Canada is also suspect because no proof exists to show that wolverine pelts attributed to Quebec or Labrador actually came from that region; animals were possibly trapped elsewhere and the pelts shipped through the eastern provinces (COSEWIC 2003, p. 20). Wolverines in eastern Canada may currently exist in an extremely lowdensity population, or may be extirpated. Wolverines in eastern Canada, both historically and currently, could represent migrants from western populations that never became resident animals (COSEWIC 2003, pp. 20 21). The Federal Government of Canada has completed a recovery plan for the eastern population with the goal of establishing a selfsustaining population through reintroduction and protection (Fortin et al. 2005, p. 16).
Wolverines in western Canada and Alaska inhabit a variety of
habitats from sea level to high in mountains (Slough 2007, pp. 7778).
They occur in Ontario, Manitoba, Saskatchewan, Alberta, British
Columbia, Yukon, Northwest Territories, and Nunavut (Slough 2007, pp.
7778). Since European colonization, a generally recognized range
contraction has taken place in boreal Ontario and the aspen parklands
of Manitoba, Saskatchewan, and Alberta (COSEWIC 2003, pp. 2021; Slough
2007, p. 77). This range contraction occurred concurrently with a
reduction in wolverine records for the Great Lakes region in the
contiguous United States (Aubry et al. 2007, pp. 21552156). Causes of
these changes are uncertain, but may be related to increased harvest,
habitat modification, or climate change (COSEWIC 2003, pp. 2021; Aubry
et al. 2007, pp. 21552156; Slough 2007, pp. 7778). Analysis supports
climate change as a contributing factor to declines in southern
Ontario, because snow conditions necessary to support wolverines do not
currently exist in the Great Lakes region of the contiguous United
States, and are marginal in southern Ontario (Aubry et al. 2007, p. 2154). It is not known if these snow
conditions existed historically in the Great Lakes of the contiguous United States, however, the small number of wolverine records from this area suggests that they did not. It is possible that suitable snow conditions did reach further south in eastern Canada in 1850 than they do today, making wolverine dispersal attempts from Canada to the Great Lakes region of the contiguous United States more likely than they are now. Wolverines occurred historically on Vancouver Island and have been given status as a separate subspecies by some (Hall 1981, p. 109). The Vancouver Island population is now regarded as possibly extirpated; no sightings have occurred since 1992 (COSEWIC 2003, p. 18).
Wolverines in western Canada and Alaska appear to persist everywhere that habitat and climate conditions are suitable (COSEWIC 2003, pp. 1321; Aubry et al. 2007, pp. 21522155; Slough 2007, p. 79; Copeland et al. 2010, Figure 2). Throughout this area, wolverines are managed by regulated harvest at the Provincial and State level. Population estimates for Canada and Alaska are rough because no wolverine surveys have taken place at the State or Provincial scale. However, the population in western Canada is estimated to include approximately 15,089 to 18,967 individuals (COSEWIC 2003, p. 22). The number of wolverines in Alaska is unknown, but they appear to exist at naturally low densities in suitable habitats throughout Alaska (Alaska Department of Fish and Game 2004, pp. 1359). We have no information to indicate that wolverine populations have been reduced in numbers or geographic range in Alaska.
The Complexity of Geographic Range Delineation
Delineating wolverine historical and present range is inherently difficult for several reasons. Wolverines tend to live in remote and inhospitable places away from human populations where they are seldom encountered, documented, or studied. Wolverines naturally occur at low population densities and are rarely and unpredictably encountered where they do occur. Wolverines often move long distances in short periods of time, when dispersing from natal ranges, into habitats that are unsuitable for longterm survival (Aubry et al. 2007, p. 2147; Moriarty et al. 2009, entire; Inman et al. 2009, pp. 2228; Brian 2010, p. 3). Such movements make it difficult to distinguish with certainty between occurrence records that represent established populations and those that represent shortterm occupancy or exploratory movements without the potential for establishment of home ranges, reproduction, and eventually populations. These natural attributes of wolverines make it difficult to precisely determine their present range, or trends in range expansion or contraction that may have occurred in the past. Therefore, we must be cautious and use multiple lines of evidence when trying to determine where past wolverine populations occurred.
Throughout the remainder of this finding, we focus on the use of verifiable and documented wolverine occurrence records to define historic and present range because we have determined that these records constitute the best scientific information available on the past and present distribution of wolverines (See Aubry et al. 2007, p. 2148). Verifiable records are records supported by physical evidence such as museum specimens, harvested pelts, DNA samples, and diagnostic photographs. Documented records are those based on accounts of wolverines being killed or captured. Use of only verifiable and documented records avoids mistakes of misidentification often made in eyewitness accounts of visual encounters. Visualencounter records often represent the majority of occurrence records for elusive forest carnivores, and their inherently high rate of misidentification of the species involved can result in wildly inaccurate conclusions about species occurrence (McKelvey et al. 2008, entire). The paper by Aubry et al. (2007, entire) utilized only verifiable and documented records to investigate wolverine distribution through time. This paper is the only available comprehensive treatment of these distribution patterns that attempts to distinguish between records that represent resident animals versus animals that have dispersed outside of suitable habitat. For these reasons we believe that Aubry et al. (2007, entire) represents the best available summary of wolverine occurrence records in the contiguous United States at this time. Since the publication of Aubry et al. (2007, entire), verified records of wolverine have also been documented in Colorado and California, which we will describe in greater detail below.
Aubry et al. (2007, entire) used verifiable and documented records from museum collections, literature sources, and State and Federal institutions to trace changes in geographic distribution of wolverines in the historic record. They then used an overlay of suitable wolverine habitats to further refine which records represent wolverines in habitats that may support residency, and by extension, populations, and which records likely represent wolverines outside the range of suitable habitats, so called ``extralimital'' records. Aubry et al.'s (2007, entire) focus on verifiable and documented records corrected past overly broad approaches to wolverine range mapping (Nowak 1973, p. 22; Hall 1981, p. 1009; Wilson 1982, p. 644; Hash 1987, p. 576) that used a more inclusive but potentially misleading approach when dealing with occurrence records. Many of the extralimital records used in these publications represent individuals dispersing from natal ranges that ended up in habitats that cannot support wolverines, and the use of this data to determine the historic geographic range of wolverines results in gross overestimation of the area that can actually be used successfully by wolverines for the establishment of populations. Subsequent to publication of Aubry et al. (2007, entire), Copeland et al. (2010, entire) further refined our understanding of wolverine habitat needs and corroborated the approach of Aubry et al. (2007, entire).
We agree with Aubry et al. (2007, p. 2149) that the most
appropriate method to determine the current and historic range of
wolverines is to use a combination of occurrence records and habitat
suitability, along with other information, such as documented
successful reproduction events, that indicate where reproductive and
potentially selfsustaining populations may occur. We also generally
agree with their conclusions about the historic and current range of
the species. We believe that the species' range is the area that may
support viable populations, and does not include extralimital
occurrences outside of habitat that is likely to support wolverine
lifehistory needs. Areas that can support wolverine populations may be
referred to as potential ``source'' populations because they provide
surplus individuals through reproduction beyond what is needed for
replacement. Areas that do not have the habitat to support viable
populations may be referred to as population ``sinks'' because
wolverines may disperse to these areas and remain for some time, but
will either die there without reproducing, leave the area in search of
better habitat conditions, or may actually reproduce, but at a rate
lower than that needed for replacement of individuals lost to mortality
or emigration, leading to eventual population extinction. For a widely
dispersing species like wolverines, we expect many locality records to
represent dispersers into sink habitats. The value to the population (and thus
the DPS) of these dispersers in sink habitat is unclear; however, it is likely that most dispersers into sink habitats will be lost to the population unless they are able to move back into source habitats. Therefore, it is our belief that population sink areas, here defined as places where wolverines may be found but where habitat is not suitable for longterm occupancy and reproduction, do not represent part of the species historic range and have little conservation value for the DPS, other than possibly serving as waystations for attempted dispersers as they search for suitable habitats. This approach to defining historic range results in reducing the bias of extralimital dispersers and concentrates conservation attention on areas capable of maintaining populations, and is more in keeping with the intentions of the Act, than broader depictions of geographic range.
Aubry et al. (2007, pp. 21472148) divided records into ``historical'' (recorded prior to 1961), ``recent'' (recorded between 1961 and 1994), and ``current'' (recorded after 1994). Historical records occurred before systematic surveys. Historical records encompass the time during which wolverine numbers and distribution were hypothesized to be at their highest (prior to European settlement) and also at their lowest (early 20th Century) (Wright and Thompson 1935; Grinnell et al. 1937; Allen 1942; Newby and Wright 1955, all as cited in Aubry et al. 2007, p. 2148). The recent time interval covers a hypothesized population expansion and rebound from the early 20th Century low. Current records offer the most recent evidence available for wolverine occurrences and potential populations. We believe all occurrence records must be individually analyzed in light of their context in terms of habitat conditions conducive to wolverine population establishment and whether or not they occur clustered with other records, which might indicate that populations have historically occurred in the area. The authors of Aubry et al. (2007) did such an analysis as they compiled their records.
Of 729 mappable records (those records with precise location
information) compiled by Aubry et al. (2007, p. 2150), 188 were from
the historical time interval (see Figure 1). We assessed the
historical, recent, and current distribution data for each of the
regions below to determine the likelihood of the presence of historical
populations (rather than extralimital dispersers). The discussion below
draws heavily from both Aubry et al. (2007, entire) and Copeland et al. (2010, entire).
Table 1Wolverine Records From Three Time Periods From Aubry et al. 2007. [Numbers Represent Total Documented and Verifiable Records With the Subset of Those Records That Were Verifiable in Parentheses] Historical (< Recent (1961 Current (> 1964) 1994) 1994) Northeast....................................................... 13 (1) 0 0 Upper Midwest................................................... 4 (2) 0 0 Great Lakes..................................................... 36 (4) 1 0 Central Great Plains............................................ 71 * (2) 1 0 Rocky Mountains................................................. 147 (45) 332 (283) 215 (210) Pacific Coast................................................... 89 (14) 23 (15) 7
Totals...................................................... 362 (68) 357 (298) 222 (210) * 35 records from a single source (the journals of Alexander Henry).
Northeast and Upper MidwestThe low number of records and scattered nature of their distribution combined with a lack of suitable habitat indicate that wolverines were likely only occasional transients to the area and not present as a reproducing population after 1800.
Great LakesThe lack of large numbers of verifiable records in this area of relatively high human population density and the lack of suitable habitat suggests that wolverines did not exist in this area as a viable population after 1900. Widely scattered records generally before 1900, with an occasional record after that year, suggest that if a reproducing population existed in the Great Lakes, it predated 1900, and that post1900 records represent dispersal from a receding Canadian population. Wolverine distribution in Ontario, Canada, appears to have receded north from the Great Lakes region since the 1800s, and currently wolverines occupy only the northern portion of the province, a distance of over 400 miles from the U.S. border (COSEWIC 2003, p. 9). The pattern of record distribution illustrated in Aubry et al. (2007, p. 2152) is consistent with what would be expected if those records were of dispersing individuals from a Canadian population that receded progressively further north into Canada after 1900, possibly due to natural climate changes.
Central Great PlainsThe lack of precise locality records and suitable habitat from the Great Plains States leads us to conclude that reproducing populations of wolverines did not historically inhabit this area. Thirtyfive of thirtysix records from North Dakota are from the journals of a single fur trader (see Table 1), and it is not clear that the records represent actual collection localities or are localities where trades or shipments occurred (Aubry 2007, pers. comm.). Given the habitat relationships of wolverines (e.g., Copeland et al. 2010, Figure 1), it is unlikely that these records represent established wolverines or that this area was in any way wolverine habitat.
Rocky MountainsFive Rocky Mountains States (Idaho, Montana,
Wyoming, Colorado, and Utah) contained numerous wolverine records.
Records with precise locality information appear to coalesce around
several areas that may have been population centers, such as central
Colorado, the greater Yellowstone region, and northern Idaho
northwestern Montana. The large number of verifiable and documented
records for this region, along with the suggestion of population
centers or strongholds, suggests that wolverines existed in reproducing
populations throughout much of the Rocky Mountains during the
historical time interval. The lack of records for Colorado and Utah
after 1921 suggests that the southern Rocky Mountain population of
wolverines was extirpated in the early 1900s, concurrent with [[Page 78035]]
widespread systematic predator control by government agencies and livestock interests. The northern Rocky Mountain population (north of Wyoming) was reduced to historic lows or possibly even extirpated during the early 1900s, and then increased dramatically in the second half of the 1900s (see Table 1) as predator control efforts subsided and trapping regulations became more restrictive (Aubry et al. 2007, p. 2151). This increase likely indicates a population rebound from historic lows in this period.
Wolverine records from 1995 to 2005 indicate that wolverine populations currently exist in the northern Rocky Mountains (see Table 1). Legal trapping in Montana in the recent past removed an average of 10.5 individuals from this population each year (Montana Department of Fish, Wildlife, and Parks 2007, p. 2), and harvest mortality has been reduced due to regulatory changes in 2008 (Montana Department of Fish, Wildlife and Parks 2008, p. 8). Populations in British Columbia and Alberta, Canada, are extant (COSEWIC 2003, pp. 1819), and may have been a source of surplus wolverines to the contiguous U.S. population during population lows. Recently, a male wolverine moved on its own from the southern Greater Yellowstone Area of Wyoming into the southern Rocky Mountains of Colorado where it still persisted as of August 2010 (Inman et al. 2009, pp. 2226; Inman 2010, pers. comm.). This attempted dispersal event is the first verified wolverine occurrence in Colorado since 1919 and may represent a continuation of the wolverine expansion in the Rocky Mountains detailed above. It is possible that other wolverines have travelled to the southern Rocky Mountains and have remained undetected. There is no evidence that Colorado currently hosts a wolverine population or that female wolverines have made, or are likely to make, similar movements.
Pacific CoastHistorically, wolverines occurred in two population centers in the North Cascades Range and the Sierra Nevada. These areas are separated by an area with no historic records (southern Oregon and northern California), indicating that the historical distribution of wolverines in this area is best represented by two disjunct populations rather than a continuous peninsular extension from Canada. This conclusion is supported by genetic data indicating that the Sierra Nevada and Cascades wolverines were separated for at least 2,000 years prior to extirpation of the Sierra Nevada population (Schwartz et al. 2007, p. 2174).
Only one Sierra Nevada record exists after 1930, indicating that this population was likely extirpated in the first half of the 1900s concurrent with widespread systematic predator control programs. In 2008, a male wolverine was discovered in the Sierra Nevada Range of California, the first verified record from California since 1922 (Moriarty et al. 2009, entire). Genetic testing revealed that this wolverine was not a descendant of the endemic Sierra Nevada wolverine population, but was likely derived from wolverines in the Rocky Mountains (Moriarty et al. 2009, p. 159). This attempted dispersal event may represent a continuation of the wolverine expansion in the contiguous United States as detailed above. Other wolverines may have traveled to the Sierra Nevada and remain undetected. There is no evidence that California currently hosts a wolverine population or that female wolverines have made or are likely to make similar dispersal movements.
Wolverines were likely extirpated from the North Cascades in the early 20th century and then recently recolonized from Canada. Currently, a small population persists in this area (Aubrey et al. 2009, entire). The Northern Cascades population may be connected with, and is possibly dependent on, the larger Canadian population for future expansion and longterm persistence.
Summary of Wolverine Distribution
Historical wolverine records were found across the northern tier of the contiguous United States with convincing evidence of wolverine populations in the northern and southern Rocky Mountains, Sierra Nevada Mountains, and North Cascades Mountains (Aubry et al. 2007, p. 2152).
Currently, wolverines appear to be distributed as functioning populations in two regions in the contiguous United States: The North Cascades in Washington, and the northern Rocky Mountains in Idaho, Montana, and Wyoming. Wolverines were likely extirpated, or nearly so, from the entire contiguous United States in the first half of the 20th Century (Aubry et al. 2007, Table 1). The available evidence suggests that, in the second half of the 20th Century and continuing into the present time, wolverine populations have expanded in the North Cascades and the northern Rocky Mountains, but that populations have not been reestablished in the Sierra Nevada Range or the southern Rocky Mountains. We conclude that the current range of the species in the contiguous United States includes the North Cascades Mountains, the northern Rocky Mountains, the southern Rocky Mountains, and the Sierra Nevada Mountains, but that reestablishment of populations in the southern Rocky Mountains and Sierra Nevada has not yet occurred.
We also conclude that wolverines either did not exist as established populations, or were extirpated prior to settlement and the compilation of historical records, in the Great Lakes region, possibly due to climate changes that occurred through the 1800s and 1900s. The Great Lakes region lacks suitable wolverine habitat, and suitable habitat does not appear to exist in adjacent Canada (Copeland et al. 2010, Figure 1). The widely scattered records from this region are consistent with dispersing individuals from a Canadian population that receded north early in the 1800s. We cannot rule out the possibility that wolverines existed as established populations prior to the onset of trapping in this area, but we have no reliable evidence that they did.
No reliable evidence in the historical records indicates that wolverines were ever present as established populations in the Great Plains, Midwest, or Northeast.
Habitat Relationships and Wolverine Distribution
Deep, persistent, and reliable spring snow cover (April 15 to May
14) is the best overall predictor of wolverine occurrence in the
contiguous United States (Aubry et al. 2007, pp. 21522156; Copeland et
al. 2010, entire). Deep persistent snow correlates well with wolverine
yearround habitat use across wolverine distribution in North America
and Eurasia at both regional and local scales (Copeland et al. 2010,
entire). It is uncertain why spring snow cover so accurately predicts
wolverine habitat use; however, it is likely related to wolverines'
need for deep snow during the denning period, and also wolverines'
physiological requirement for yearround cold temperatures (Copeland et
al. 2010, pp. 242243). Snow cover during the denning period is
essential for successful wolverine reproduction rangewide (Hatler
1989, p. iv; Magoun and Copeland 1998, p. 1317; Inman et al. 2007c, pp.
7172; Persson 2007; Copeland et al. 2010, p. 244). Wolverine dens tend
to be in areas of high structural diversity such as logs and boulders
with deep snow (Magoun and Copeland 1998, p. 1317; Inman et al. 2007c,
pp. 7172; Persson 2007, entire). Reproductive females dig deep snow
tunnels to reach the protective structure provided by logs and boulders. This behavior presumably protects the
vulnerable kits from predation by large carnivores, including other wolverines (Pulliainen 1968, p. 342; Zyryanov 1989, pp. 312), but may also have physiological benefits for kits by buffering them from extreme cold, wind, and desiccation (Pullianen 1968, p. 342, Bj[auml]rvall et al. 1978, p. 23). Wolverines live in lowtemperature conditions and appear to select habitats in part to avoid high summer temperatures (Copeland et al. 2010, p. 242). Wolverine distribution is likely affected by climatic conditions at two different scales. Wolverines require deep persistent snow for denning, and this likely determines where wolverine populations can be found at the grossest rangewide scale (Copeland et al. 2010, p. 244). At smaller scales, wolverines likely select habitats to avoid high summer temperatures. These cool habitats also tend to retain snow late into spring, leading to wolverines' yearround association with areas of persistent spring snow (Copeland et al. 2010, p. 244).
All of the areas in the contiguous United States for which good evidence of persistent wolverine populations (either present or historic) exists (i.e., North Cascades, Sierra Nevada, northern and southern Rocky Mountains) contain large and welldistributed areas of deep snow cover that persists through the wolverine denning period (Brock et al. 2007, pp. 3653; Aubry et al. 2007, p. 2154; Copeland et al. 2010, Figure 1). The Great Plains, Great Lakes, Midwest, and Northeast lack the spring snow conditions and low summer temperatures thought to be required by wolverines for successful reproduction and yearround occupancy (Aubry et al. 2007, p. 2154; Copeland et al. 2010, Figure 1). The lack of persistent spring snow conditions in the Great Plains, Great Lakes, Midwest, and Northeast supports the exclusion of these areas from the current range of wolverines. Whether wolverines once existed as established populations in any of these regions is uncertain, but the current climate appears to preclude their presence as reproducing populations now, and the sparse historical record of wolverine presence in this area makes historic occupation of these areas by wolverine populations doubtful. It is our conclusion that the ecosystem that supports wolverines does not exist in these areas currently, and may never have existed in the past.
Large areas of habitat with characteristics suitable for wolverines still occur in the southern Rocky Mountains and Sierra Nevada, despite the extirpation of wolverines from those areas (Aubry et al. 2007, p. 2154, Brock et al. 2007, p. 26; Copeland et al. 2010, Figure 1). Wolverine extirpations in these areas were coincident with systematic predator eradication efforts in the early 1900s, which have been discontinued for many years. Each of these areas has received at least one and possibly more migrants from adjacent populations in the northern Rocky Mountains; however, there is no evidence that females have migrated to these areas or that populations of wolverines exist in them (Aubry et al. 2007, Table 1; Moriarty et al. 2009, entire; Inman et al. 2009, entire).
We conclude that areas of wolverine historical occurrence can be
placed in one of three categories: (1) Areas where wolverines are
extant as reproducing and potentially selfsustaining populations
(North Cascades, northern Rocky Mountains); (2) areas where wolverines
historically existed as reproducing and potentially selfsustaining populations prior to humaninduced extirpation, and where
reestablishment of those populations is possible given current habitat condition and management (the Sierra Nevada Mountains in California and southern Rocky Mountains in Colorado, New Mexico, Wyoming, and Utah); and (3) areas where historical presence of wolverines in reproducing and potentially selfsustaining populations is doubtful, and where the current habitat conditions preclude the establishment of populations (Great Plains, Midwest, Great Lakes, and Northeast). We, therefore, consider the current range of wolverines to include suitable habitat in the North Cascades of Washington and possibly Oregon, the northern Rocky Mountains of Idaho, Wyoming, and Montana, the southern Rocky Mountains of Colorado, Utah, and Wyoming, and the Sierra Nevada of California. We here include the Sierra Nevada and southern Rocky Mountains in the current range of wolverines despite the probability that functional populations do not exist in these areas. They are included due to the known existence of one individual in each area and the possibility that more, as yet undetected, individuals inhabit these areas.
Distinct Population Segment
Pursuant to the Act, we must consider for listing any species, subspecies, or, for vertebrates, any Distinct Population Segment (DPS) of these taxa, if there is sufficient information to indicate that such action may be warranted. To interpret and implement the DPS provision of the Act and Congressional guidance, the Service and the National Marine Fisheries Service published, on February 7, 1996, an interagency Policy Regarding the Recognition of Distinct Vertebrate Population Segments under the Act (61 FR 4722). This policy addresses the recognition of DPSs for potential listing actions. The policy allows for more refined application of the Act that better reflects the biological needs of the taxon being considered, and avoids the inclusion of entities that do not require its protective measures.
Under our DPS policy, three elements are considered in a decision
regarding the status of a possible DPS as endangered or threatened
under the Act. These are applied similarly for additions to the list of
endangered and threatened species, reclassification, and removal from
the list. They are: (1) Discreteness of the population segment in
relation to the remainder of the taxon; (2) the biological or
ecological significance of the population segment to the taxon to which
it belongs; and (3) the population segment's conservation status in
relation to the Act's standards for listing (i.e., whether the
population segment is, when treated as if it were a species or
subspecies, endangered or threatened). Discreteness refers to the
degree of isolation of a population from other members of the species,
and we evaluate this based on specific criteria. If a population
segment is considered discrete, we must consider whether the discrete
segment is ``significant'' to the taxon to which it belongs by using
the best available scientific and commercial information. If we
determine that a population segment is both discrete and significant,
we then evaluate it for endangered or threatened status based on the
Act's standards. The DPS evaluation in this finding concerns the
segment of the wolverine species occurring within the 48 States,
including the northern and southern Rocky Mountain physiographic provinces, Sierra Nevada Range, and North Cascades Range.
Distinct Population Segment Analysis for Wolverine in the Contiguous United States
Analysis of Discreteness
Under our DPS Policy, a population segment of a vertebrate species
may be considered discrete if it satisfies either one of the following
conditions: (1) It is markedly separated from other populations of the
same taxon as a consequence of physical, physiological, ecological, or
behavioral factors (quantitative measures of genetic or morphological
discontinuity may provide evidence of this separation); or (2) it is
delimited by international governmental boundaries within which [[Page 78037]]
differences in control of exploitation, management of habitat, conservation status, or regulatory mechanisms exist that are significant in light of section 4(a)(1)(D) of the Act (inadequacy of existing regulatory mechanisms). The wolverine within the contiguous United States meets the second DPS discreteness condition because of differences in conservation status as delimited by the CanadianU.S. international governmental boundary.
Discreteness Based on the International BorderDifferences in Conservation Status
We find that differences in conservation status of the wolverine between the United States and Canada are substantial and significant in light of section 4(a)(1)(D) of the Act. In the remaining current range in CanadaAlaska, wolverines exist in welldistributed, interconnected, large populations. Conversely, wolverine populations in the remaining U.S. range appear to be at numbers so low that their continued existence could be at risk, especially as considered in light of the five threat factors discussed below. These risks come from three main factors: (1) Small total population size; (2) effective population size below that needed to maintain genetic diversity and demographic stability; and (3) the fragmented nature of wolverine habitat in the contiguous United States that results in smaller, isolated ``sky island'' patches separated by unsuitable habitats. It is apparent that maintaining wolverines within their native range in the contiguous United States into the future is likely to require regulatory mechanisms that are not currently in place. These three factors are explained in more detail below.
The total population sizes for CanadaAlaska and the contiguous United States differ by more than an order of magnitude. The contiguous U.S. population likely numbers approximately 250 to 300 individuals (Inman 2010b, pers. comm.). This contrasts with western Canada, where wolverine populations are estimated at 15,089 to 18,967 individuals (COSEWIC 2003, p. 22). Wolverine population size in Alaska is unknown; however, the average annual harvest exceeds 500 individuals and the population does not appear to be in decline (Alaska Department of Fish and Game 2004, entire), indicating that the population is likely to number over ten thousand individuals (calculated using demographic data in Lofroth and Ott 2007, pp. 21962198; assumes sustainable harvest). The difference in total population size coincides with the international boundary between the contiguous United States and Canada. Wolverine populations number 2,0893,567 in British Columbia and 1,500 2,000 in Alberta (COSEWIC 2003, p. 22), the two provinces immediately adjacent to the contiguous U.S. wolverine population. The difference in total population sizes is significant because critically small populations such as those in the contiguous United States face higher extinction risk than large ones such as the CanadaAlaska population. Therefore, the contiguous U.S. population is more vulnerable to extinction, and thus of poor conservation status, relative to the more secure CanadaAlaska population.
Wolverines in Canada's eastern provinces are listed under the Species at Risk Act of Canada. Wolverines in the eastern provinces appear to have been extirpated by the early 20th century (COSEWIC 2003, p. 20). There is a general lack of reliable historic information on wolverines in this area, and significant doubt exists about whether a population ever occurred there historically (COSEWIC 2003, p. 20). For the purposes of this finding, we considered the Canadian wolverine population to include only wolverines from Ontario west to the Pacific coast and Alaska, and assumed that wolverines in eastern Canada were either extirpated or are at such low numbers as not to be part of a functioning population. It is our determination that the conservation status of the eastern population, if it does indeed exist, is not relevant to the discreteness analysis for this DPS for the following reasons: (1) If wolverines currently reside in the eastern Canadian Provinces, they are likely disjunct from wolverines in western Canada (COSEWIC 2003, Figure 3); and (2) there is significant doubt that wolverine populations existed in this part of Canada historically, so the current lack of evidence of a population may not represent a degradation of species status in this area (COSEWIC 2003, pp. 2021).
The second substantial difference in wolverine status between the contiguous United States and Canada is reflected in the size of the effective populations. Population ecologists use the concept of a population's ``effective'' size as a measure of the proportion of the actual population that contributes to future generations (for a review of effective population size, see Schwartz et al. 1998, entire). In a population where all of the individuals contribute offspring equally, effective population size would equal true population size. For populations where contribution to the next generations is often unequal, effective population size will be smaller than the true or ``census'' population size. The smaller the effective population size, the more reproduction is dominated by a few individuals. Effective population size is important because it determines rates of loss of genetic variation, fixation of deleterious alleles and the rate of inbreeding. Populations with small effective population sizes show reductions in population growth rates and increases in extinction probabilities (Leberg 1990, p. 194; Jimenez et al. 1994, pp. 272273; Newman and Pilson 1997, p. 360; Saccheri et al. 1998, p. 492; Reed and Bryant 2000, p. 11; Schwartz and Mills 2005, p. 419; Hogg et al. 2006, p. 1495, 1498; Allendorf and Luikart 2007, pp. 338342). Franklin (1980, as cited in Allendorf and Luikart 2007, p. 359) proposed an empirically based rule suggesting that for shortterm (a few generations) maintenance of genetic diversity, effective population size should not be less than 50. For longterm (hundreds of generations) maintenance of genetic diversity, effective population size should not be less than 500 (for appropriate use of this rule and its limitations see Allendorf and Luikart 2007, pp. 359360). Others suggest that even higher numbers are required to ensure that populations remain viable, suggesting that longterm connectivity to the reservoir of genetic resources in the Canadian population of wolverines will be required (Traill et al. 2010, p. 32).
Wolverine effective population size in the largest extant
population in the contiguous United States is exceptionally low
(Schwartz personal communication 2007, entire) and is below what is
thought necessary for shortterm maintenance of genetic diversity.
Effective population size for wolverines in the Rocky Mountains
averaged 39 (Schwartz personal communication 2007, entire) (this study
excluded the small population from the Crazy and Belt Mountains
(hereafter ``CrazyBelts'') as they may be an isolated population, which
could bias the estimate using the methods of Tallmon et al. (2007,
entire)). Measures of the effective population sizes of the other
populations in the contiguous United States have not been completed,
but given their small census sizes, their effective sizes are expected
to be smaller than for the northern Rocky Mountain population. Thus,
wolverine effective population sizes are very low. For comparison,
estimates of wolverine effective population size are bracketed by
critically endangered species like the blackfooted ferret (4.10) (Wisely et al.
2007, p. 3) and ocelots (2.9 to 13.9) (Janecka et al. 2007, p. 1), but substantially smaller than estimates for the Yellowstone Grizzly bear (greater than 100), which has reached the level of recovery under the Act (Miller and Waits 2003, p. 4338). Therefore, we conclude that effective population size estimates for wolverines do not suggest that populations are currently critically endangered, but they do suggest that populations are low enough that they could be vulnerable to loss of genetic diversity, and may require intervention in the future to remain viable.
The concern with the low effective population size is highlighted in recent research that determined that, absent immigration, at least 400 breeding pairs would be necessary to sustain longterm genetic viability of the contiguous U.S. wolverine population (Cegelski et al. 2006, p. 197). However, the entire population is likely 250300 (Inman 2010b, pers. comm.), with a substantial number of these being nonbreeding subadults. Furthermore, the U.S. population appears to be split into at least five smaller subpopulations (Northern Cascades, CrazyBelts, Idaho, Greater Yellowstone Ecosystem, and Northern Montana) that are semiisolated from each other, meaning that genetic exchange does not occur frequently enough to prevent genetic drift (changes in genetic composition due to random sampling in small populations) and loss of genetic diversity (Cegelski et al. 2006, p. 206) further reducing the effective population size. Based on available scientific and commercial information, it does not appear that any of the wolverine populations that historically existed in the contiguous United States would have had effective population sizes approaching 400 animals. Therefore, it is likely that connectivity to Canadian populations to the north would have been necessary to maintain genetic diversity in these populations prior to European settlement.
The concern that low effective population size may result in negative effects is already being realized for the contiguous U.S. population of wolverine. Genetic drift has occurred in the remaining populations in the contiguous United States: wolverines here contain 3 of 13 haplotypes (sets of closely linked genetic markers that are inherited together) found in Canadian populations (Kyle and Strobeck 2001, p. 343; Cegelski et al. 2003, pp. 29142915; Cegelski et al. 2006, p. 208; Schwartz et al. 2007, p. 2176; Schwartz et al. 2009, p. 3229). The haplotypes found in these populations are a subset of those in the larger Canadian population, indicating that genetic drift had caused a loss of genetic diversity. A single haplotype dominates the northern Rocky Mountain wolverine population, with 71 of 73 wolverine sampled expressing that haplotype (Schwartz et al. 2007, p. 2176). The reduced number of haplotypes indicates not only that genetic drift is occurring, but also that there is some level of genetic separation; if these populations were freely interbreeding, they would share more haplotypes. The reduction of haplotypes is likely a result of small population size and the fragmented nature of wolverine habitat in the United States and is consistent with an emerging pattern of reduced genetic variation at the southern edge of the range documented in a suite of boreal forest carnivores (Schwartz et al. 2007, p. 2177). Whether or not the wolverine population in the contiguous United States has suffered any deleterious effects due to this reduction in genetic diversity is unknown. However, based on principles of conservation genetics, we do expect that reduced genetic diversity would make this population more vulnerable to other threats due to reduced genetic resiliency and reduced ability to adapt to change (Allendorf and Luikart 2007, pp. 338342).
No effective population size estimate exists for populations in Canada or Alaska; however, because of the large and contiguous nature of the population and the relatively high genetic diversity in Canada and Alaska, there is a reasonable scientific basis to conclude that the effective population size is large enough that it is not a cause for conservation concern. None of the Canadian or Alaskan populations tested show signs of genetic drift or inbreeding. This information indicates that the population does not have a low effective population size.
Reduced genetic diversity and low effective population sizes result in high extinction risk in animal populations (Frankham 1995, p. 795). The fragile nature of wolverine populations in the contiguous United States contrasts with Canada and Alaska where wolverines are relatively abundant and exist in habitats with a high level of connectivity (COSEWIC 2003, p.8; Slough 2007, p. 78).
The third substantial difference in wolverine status between the contiguous United States and Canada is reflected by the amount and distribution of available habitat for the species. Habitat in the contiguous United States consists of small isolated ``islands'' of highelevation alpine habitats separated from each other by low valleys of unsuitable habitats. Habitat islands are represented by areas containing spring snow (Copeland et al. 2010, Figure 2). Wolverine range in the contiguous United States is characterized by isolated mountain habitats dissected by lowerelevation valleys, while habitat in adjoining Canada comprises mostly large blocks of contiguous habitat (Copeland et al. 2010, Figure 2; Copeland 2010, pers. comm.). Wolverines occupy habitat at high elevations, generally above 2,100 m (6,888 ft), in the mountains of the contiguous United States. The intervening valleys in this area range from 975 m to 1,500 m (3,198 ft to 4,920 ft), and are dominated by ecosystems that are unsuitable for longterm wolverine presence, but do serve as routes for wolverine movement between suitable habitat patches. Intermountain valleys are increasingly becoming the sites of human residential and commercial developments and transportation corridors. The large distances between suitable wolverine habitats results in wolverines existing on an archipelago of suitable habitats in a sea of unsuitable habitat. The low population density and genetic diversity of wolverines in this area requires that exchange of individual wolverines between islands of habitat occurs to avoid inbreeding or local extinction due to demographic stochasticity.
Wolverine populations in the Canadian Rocky Mountains also exist on habitat islands, but the islands are much larger, so that exchange of individuals is less critical for demographic and genetic stability. Further north in Canada, where cold snowy conditions occur at lower elevations, wolverines inhabit lower elevations and valley bottom habitats (COSEWIC 2003, pp. 78). In the far north of Canada, wolverine habitat extends into lowelevation valleys and the vast expanses of lowelevation boreal forest and tundra. For these reasons, exchange of wolverines between habitat islands in the Canadian Rocky Mountains is both more likely to occur and less critical for the longterm maintenance of those populations.
In the contiguous United States, wolverines must cross unsuitable
habitats to achieve connectivity among subpopulations, which is
required to avert further genetic drift and loss of genetic diversity
(Kyle and Strobeck 2002, p. 1148; Cegelski et al. 2006, pp. 208209;
Schwartz et al. 2009, p. 3230). The highly fragmented nature of the
habitat in the contiguous United States contributes to the low
effective population size for wolverines in this area, making the
continued persistence of the population precarious relative to the CanadianAlaskan population.
Habitats in Canada and Alaska exist in larger contiguous blocks that have few or no impediments to demographic or genetic connectivity with peripheral smaller blocks (Copeland et al. 2010, Figure 2). The fragmented nature and distribution of wolverine habitat in the contiguous United States results in a population that is highly vulnerable to extirpation because of lack of connectivity between subpopulations, it also makes them more vulnerable to external threats such as those analyzed under the five threat factors below.
Conservation status of wolverines in the contiguous United States differs significantly with that of the Cana
FOR FURTHER INFORMATION CONTACT
Mark Wilson, Field Supervisor, U.S. Fish and Wildlife Service, Montana Field Office (see ADDRESSES); by telephone at 4064495225; or by facsimile at 4064495339. If you use a telecommunications device for the deaf (TDD), call the Federal Information Relay Service (FIRS) at 8008778339.