Overview

Distribution

Global Range: (20,000-200,000 square km (about 8000-80,000 square miles)) Historical range included high-elevation areas of the Sierra Nevada and Cascade mountain ranges in California, from Tulare County north to Sierra County, and from the vicinity of Lassen Peak and Mt. Shasta west to the Trinity Mountains in Trinity County, with a recent study indicating that the historical range also included the southern Cascade mountain range in Oregon, as far north as the Columbia River (see USFWS 2012).

Elevational range extended from as low as 1,180 meters in Yosemite Valley to as high as 3,630 meters in the southern Sierra Nevada (Grinnell et al. 1937, Gould 1978, Biosystems Analysis 1989, Schempf and White 1977). This fox seldom has been detected below 1,500 meters and is most often observed above 2,100 meters (Perrine et al. 2010).

The current distribution is believed to be restricted to a few small populations: one in the vicinity of Lassen Peak, another in the vicinity of Sonora Pass (Statham et al. 2012, USFWS 2012); and ocasional evidence indicating the existence of small number populations in the Cascades of Oregon (D. Clayton, J. von Kienast, K. Aubry, pers. comm., cited by Statham et al. 2012; recent photo evidence from Mt. Hood National Forest ad Crater Lake National Park). The U.S. Forest Service recently conducted carnivore surveys on National Forest System lands throughout the Sierra Nevada, but Sierra Nevada red fox were detected only in the Lassen National Forest and Humboldt-Toiyabe National Forest (see USFWS 2012).

FURTHER INFORMATION

Hall (1981) mapped the range as extending from northern and central California east through most of central Nevada. However, Hall (1946) indicated that the subspecific identity of red foxes in Nevada was uncertain; he suggested that foxes in the Sierra Nevada might be subspecifically different from at least some of those occurring farther east in Nevada. Subsequently the subspecies necator was presumed to range from the northern California Cascades east to the northern Sierra Nevada, then south through the mountains to Tulare County, though the distribution was regarded as poorly known (Biosystems Analysis 1989). As of the late 1980s, the subspecies was thought to be most numerous (though still uncommon) in the vicinity of Lassen Volcanic and Yosemite national parks, but this conclusion may have reflected the distribution and abundance of human observers rather than of foxes (California Department of Fish and Game 1987). Perrine et al. (2010) described the historical range as "throughout high elevations of the Sierra Nevada from Tulare County northward to Sierra County, and from Mount Shasta and Lassen Peak westward to the Trinity Mountains (Trinity County."
More recently, genetic studies indicated that red foxes in the Sierra Nevada should be regarded as consubspecific with those in the southern Cascades (through Oregon northward to the Columbia River) (Sacks et al. 2010). Additionally, red foxes in eastern half of Nevada appeared to be more closely related to those in the Rocky Mountains than to those in the Sierra Nevada. So the range of subspecies necator apparently encompasses the Sierra Nevada and Cacade Mountains (California, Oregon, extreme western Nevada) but not areas to the east in central and eastern Nevada.

Carlson et al. (2011) presented a map showing red fox detections (through 2007) in Lassen, Tehama, Shasta, Siskiyou, and Modoc counties, California. In August 2010, biologists on the Humboldt-Toiyabe National Forest detected a red fox at an automatic camera station near the Sonora Pass along the border of Tuolomne and Mono counties (Perrine et al. 2010). Preliminary genetic analyses conducted at UC Davis indicated that the fox was a Sierra Nevada red fox. Further surveys and analyses were planned. No confirmed recent records exist for elsewhere in the historical range in California, despite fairly widespread use of appropriate survey methods (e.g., baited "camera traps") (Perrine et al. 2010). Status of this subspecies in Oregon is unknown (Perrine et al. 2010).

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endemic to a single nation

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Physical Description

Type Information

Type for Vulpes vulpes necator
Catalog Number: USNM 30735
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Sex/Stage: Female; Young adult
Preparation: Skin; Skull
Collector(s): A. Fisher
Year Collected: 1891
Locality: Whitney Meadows, near Mount Whitney, High Sierra, Tulare County, California, United States, North America
Elevation (m): 2896
  • Type: Merriam, C. H. 1900 Dec 28. Proceedings of the Washington Academy of Sciences. 2: 664.
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Ecology

Habitat

Habitat Type: Terrestrial

Comments: This fox occurs in various habitatsf (e.g., forest openings, meadows, and barren rocky areas) in alpine and subalpine zones; preferred habitat in California apparently is red fir and lodgepole pine forests and alpine fell-fields (Ingles 1965, California DF&G 1990), though this conclusion is not based on detailed studies over most of the range.

Perrine et al. (2010) reported that "occupied habitats seem to be a composite typical of the high Sierra: high elevation barren, conifer and shrub habitats; montane meadows; subalpine woodlands and fell-fields." Summer habitat in the Lassen Peak area wasnegatively associated with shrub and herbaceous cover, whereas winter habitat was 150-500 meters lower in elevation and was positively associated with forest cover comprised of large trees (>60 cm DBH) with >40% canopy closure (Benson et al. 2005, Perrine 2005, Perrine et al. 2010). In winter, foxes followed forested edges of openings, possibly avoiding areas where they would be exposed to attack by other carnivores (Benson et al. 2005, Perrine et al. 2010). Den sites have been described as natural cavities in talus slopes or rockslides, and this fox also may use earthen dens, boulder piles, or even the space beneath vacant cabins, as has been described for other mountain foxes (Perrine et al. 2010).

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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

In the Lassen Peak region, California, five foxes had large seasonal home ranges (95% MCP; mean = 2,564 hectares in summer and 3,255 hectares in winter); summer locations averaged several hundred meters higher in elevation than winter locations (Perrine 2005).

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Trophic Strategy

Comments: Eats marmots, ground squirrels, mice, wood rats, pikas, hares, birds, grasshoppers, and fruits (Biosystems Analysis 1989).

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Population Biology

Global Abundance

50 - 1000 individuals

Comments: Current population levels are unknown, but the subspecies is believed to occur at very low density (USFWS 2012), and the total population.probably is in the hundreds at most.(fewer than 1,000).

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Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 5

Comments: This subspecies appears to be represented by a small number of occurrences (subpopulations). Because red foxes are highly mobile, distinct occurrences should encompass large areas separated by large gaps. Hence occurrences are large but few.

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Life History and Behavior

Reproduction

Mates usually in winter; 4-5 young are born in early spring, weaned in about 8 weeks (Biosystems Analysis 1989).

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N1 - Critically Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: T1 - Critically Imperiled

Reasons: Range includes the southern Cascades (Oregon and northern California) and the Sierra Nevada in California and a portion of western Nevada; conservation status is poorly known; potentially threatened by negative impacts deriving from logging, excessive livestock grazing, development, recreation, non-native red foxes, rodent control, climate change, and other factors.

Other Considerations: Secretive; rarely sighted.

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Global Short Term Trend: Unknown

Comments: Trend over the past 10 years or three generations is unknown.

Global Long Term Trend: Decline of 50 to >90%

Comments: Over the long term, distribution and abundance have declined, but the precise degree of decline is uncertain.

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Threats

Degree of Threat: High - medium

Comments: Threats are poorly understood.

Human-associated mortality has been caused by trapping (prior to the 1974 California prohibition), predator eradication programs associated with livestock or timber production, historical meadow overgrazing resulting in reduced prey populations, domestic dog-mediated disease vectors, and roadkill (Perrine et al. 2010).

Perrine et al. (2010) summarized "potential threats" as follows: expansion of non-native lowland red foxes or coyotes into high elevation areas, resulting in increased competition and potential transmission of harmful diseases and parasites; interbreeding with nonnative red foxes (may reduce genetic adaptation to local conditions); development and recreation, resulting in increased exposure to humans, vehicles and pets, and possibly facilitating dispersal of non-native red foxes, coyotes and other competitors (habituation and begging habits may increase risk of mortality at roads, campgrounds, etc.; fish poisoning disease mediated by stocking infected fish for recreational fisheries); contact with rodenticides applied for vegetation or livestock management purposes; climate change, resulting in a loss or restriction of their boreal environment or reduced snowfall. Perrine et al. (2010) concluded: "The factors likely to affect the distribution and persistence of Sierra Nevada red fox include climate change, conversion of habitat by human development, and expansion of coyotes and exotic red foxes into high-elevation areas. Recreation, including the effects of salmon poisoning and plague control activities, may represent a threat to individuals through increased risk of harm from interactions with people and pets, from disease transmission, and from contact with rodenticides, but the severity of this threat is not currently known. As noted above, the general lack of basic ecological information for this species makes the identification and analysis of threats a largely speculative exercise, and ultimately poses a risk to the effective management of the Sierra Nevada red fox and its habitat."

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Management

Management Research Needs: "The paucity of basic scientific information makes the development of a defensible conservation strategy for Sierra Nevada red fox extremely challenging. Of greatest urgency is the determination of the species'
current distribution in California. Such occurrence data can be used to further clarify habitat relationships and to identify focal locations for more intensive research efforts. This suggests a two-pronged research approach: a thorough survey of the historical range to identify local populations, using methods with a high probability of detecting red foxes; followed by intensive study of these populations. Such a pattern has already been applied, to a limited extent, in the Lassen region (Perrine 2005)." Source: Perrine et al. (2010).

"Documenting the current distribution of Sierra Nevada red fox throughout its historical range is essential...only baited camera stations have been demonstrated to reliably and unambiguously detect mountain red fox (Perrine 2005). Camera stations established to detect marten, fisher or wolverine may not detect red foxes if the bait or sensor is positioned >1 m above the ground or snow level, because red foxes seldom climb trees. In addition, seasonal movements such as those documented in the Lassen region (Perrine 2005) suggest that monitoring exclusively in summer will not fully reflect the species' distribution or habitat use. Although winter surveys would likely be more challenging, the probability of detection would likely be higher given the scarcity of food resources. Surveys conducted specifically to detect red foxes, using methods and protocols known to detect red foxes, are the most reliable method to document their current distribution. Snow track surveys...by trained observers may also be an efficient way to assess whether red foxes occur in an area. However, obtaining definitive results from snow tracks may be more difficult than with camera stations. Scat surveys with specially-trained dogs...could also be used to inventory local areas, with the added benefit that the feces could provide genetic samples (see below) and dietary information. A thorough evaluation of the range of potential inventory methods and their relative benefits needs to be conducted so that resources can be allocated efficiently." Source: Perrine et al. (2010).

"In addition to providing occurrence data, distribution surveys may be used to develop broadscale habitat relationships for the Sierra Nevada red fox. This information could then be used to evaluate management alternatives relative to the distribution and abundance of habitat utilized by the red foxes. Additionally, if individuals can be differentiated, such as by DNA or unique markings, an index of local population density could be calculated. Ideally, detection surveys would incorporate methods to obtain non-invasive genetic samples, such as through hair snags or the collection of feces. Genetic samples are essential for quantifying the extent of gene flow among local populations of Sierra Nevada red fox and among mountain fox populations in California, Nevada, Oregon, and Washington. Documenting, quantifying, and understanding the genetic structure of mountain red fox populations, and the factors affecting their connectivity and persistence are essential for successful management. Genetic samples also are needed to document whether exotic red foxes have expanded into the historical range of the Sierra Nevada red fox, especially in the southern portion of its range. Since exotic and native red foxes are morphologically similar, genetic markers need to be identified to reliably differentiate the two groups...." Source: Perrine et al. (2010).


Biological Research Needs: More information is needed on conservation status, basic biology, and impacts of various human activities (recreation, logging, cattle grazing).

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Global Protection: Few (1-3) occurrences appropriately protected and managed

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Relevance to Humans and Ecosystems

Risks

Stewardship Overview: Carlson et al. (2011) listed the following Default Protection Measures in Section II, item 32 of the Timber Harvest Program (THP): (1) The critical period is defined as February 1 through June 30. (2) During timber operations, if a red fox is observed within the plan area boundary, operations within 0.25 mile shall cease until after the critical breeding period or consultation with California Department of Fish and Game (DFG). (3) If Sierra Nevada red fox (SNRF) is discovered by camera station surveys, den search surveys, observations of adults or young, sign including scat, prey remains, and/or recent signs of den excavation within the THP area: a) operations within 0.25 miles shall cease and b) DFG shall be contacted to initiate a CESA consultation to determine appropriate protection measures. (4) LTO and RPF will be provided with instructions and education on identifying red fox, sign, and denning areas (pictures, identification).

Carlson et al. (2011) also listed default den protection measures: (1) No harvesting operations within 0.25 mile of an occupied den during the critical breeding period with the exception of hauling. (2) Truck hauling on appurtenant roads shall not occur within 500 feet of a den. (3) A special treatment area (STA) would be established around any active den that will consider and include site-specific recommendations. Further, if a den is located, a monitoring agreement should be established with the landowner to monitor the status of the den and any timber operations conducted at the den site. Duration of monitoring will be determined depending on site-specific conditions.

Perrine et al. (2010) stated that "vegetation management in Sierra Nevada red fox habitat should include activities that maintain or restore the health of montane meadows and the prey species they support. Because of the seasonal elevational movements of this species (Grinnell et al. 1937; Perrine 2005), the availability and maintenance of movement corridors from upper elevation areas to the mixed conifer zone will be important."

"Increased exposure to humans, vehicles, and pets entail additional risks to red foxes. Provision of educational materials on red fox and the importance of minimizing direct contact with red foxes may be helpful in reducing undesirable behaviors on the part of foxes and minimize their exposure to disease. Availability of bear-proof garbage cans and food storage lockers in campgrounds, particularly in areas used during the winter, may help curb red fox scavenging in these areas." (Perrine et al. 2010)

In the Lassen region, radio-collared red foxes were highly mobile, with large home ranges and extensive daily and seasonal movements (Perrine 2005). "Successful management of these foxes will therefore require coordination and cooperation among multiple agencies and stakeholders, including the USDA Forest Service, the National Park Service, California Department of Fish and Game, California Department of Forestry and Fire Prevention, and private forests and landowners" (Perrine et al. 2010).

"Ultimately, successful conservation will require identifying and addressing limiting factors, with particular emphasis on reproduction and mortality. Inventory methods such as cameras and snow tracks can document habitat use, but they provide little insight into survival and fecundity (other than detecting pups in an area). Information on habitat associations in the absence of demographic data may be misleading, as densely populated habitats may not be the most suitable...Assessing individual fitness requires individually marked and monitored animals. Identifying sources of mortality that are directly linked to human activities would also be particularly important. Additional information needs include fine-scale documentation of habitat use, especially habitats used for natal dens, seasonal changes in habitat use, and elevational movement patterns. This information is important but will be more difficult to collect than presence-absence data because it requires the use of intensive techniques such as radio-telemetry and mark-recapture. Clearly, such intensive local studies would also be an additional source of genetic data, which would be essential for determining the extent of genetic variability within local populations.

"Developing both extensive and intensive data-gathering efforts focused on Sierra Nevada red fox offers the best combination of information to inform management and conservation efforts. Extensive surveys can provide occurrence and broad-scale habitat associations and may provide genetic samples necessary for describing the genetic structure of red fox populations. Collaboration among local, state and federal entities would facilitate the compilation of genetic material. Such entities obviously include...land management agencies...but should also include other agencies that may have the opportunity to collect specimens, such as the California Highway Patrol, California Department of Transportation, state and federal Wildlife Services agents, local animal control officers, and academic or agency biologists operating at high elevations in the Sierra Nevada and Cascades in California. Coordination of these efforts would likely require the establishment of a central contact or clearing house, which would also compile the resulting specimens and data. Genetic information may also be obtained from intensive studies involving mark-recapture or radio-telemetry techniques through the collection of tissue, hair, or scat from captured animals. Intensive studies would offer insights into reproduction, survival, diet, and fine-scale habitat use and may help identify significant mortality factors and important habitat elements. These data are essential for the development of a comprehensive conservation strategy for the Sierra Nevada red fox in California." Source: Perrine et al. (2010).

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Wikipedia

Sierra Nevada red fox

For other uses, see Red fox .

The Sierra Nevada red fox (Vulpes vulpes necator), also known as the High Sierra fox is a subspecies of red fox and one of the most endangered mammals in North America. Until recently, only a few dozen were known to exist in a remnant population near Lassen Volcanic National Park. Recent webcam discoveries of two additional surviving remnant populations near Sonora Pass in 2010 and on Mount Hood, Oregon in 2012 raise hopes for the species' survival. The State of California banned trapping of the Sierra Nevada red fox in 1980, after annual pelt takes had dwindled to 2 per year by the 1970s. It is considered to be critically endangered by the California Department of Fish and Game.[1] On April 26, 2011, the Center for Biological Diversity petitioned the federal government to protect the High Sierra fox under the Endangered Species Act.[2] One serious threat to the Sierra Nevada red fox would be interbreeding with non-native red foxes which have been introduced into California's (Central Valley, San Francisco Bay Area and southern California) from America's eastern and midwestern populations.[3] With only about 50 animals remaining, the U.S. Fish and Wildlife Service announced on Dec. 30, 2011 that it is beginning a full status review, in response to the petition.[4]

Description[edit]

The Sierra Nevada red fox is distinguished from members of the introduced lowland population of red foxes by its slightly smaller size and darker colored fur, and by its limited geographical range above 4,500 feet. Red fox fur was sought after by trappers during the early part of last century because it was softer than California’s grey fox.[1]

Range[edit]

Red foxes (Vulpes vulpes) are distributed worldwide and in virtually all habitats, however there are three subalpine subspecies whose range is restricted to alpine and subalpine meadows and montane boreal forests, of which the Sierra Nevada red fox is one of the latter. In 1906 naturalist Frank Stephens described the High Sierra fox as occurring only above 6,000 feet in the Sierra Nevada and was initially described at 9,500 feet in Whitney Meadows, Mt. Whitney.[5] Its historical distribution was Oregon's Cascades north to the Columbia River and south to California's southern Sierra Nevada Mountains. Grinnell stated that the Sierra Nevada red fox was "“restricted to the highest timbered peaks and ridges of the main Sierra Nevada,” not occurring below 4500 feet, and considered the Lassen Peak region to be a major population center.[6] Perrine's study of Mt. Lassen using 144 baited motion-sensitive cameras from 1997-2002 found no foxes below 4520 feet as well.[7] The Lassen foxes all had the same Mitochondrial DNA (mtDNA) haplotype, which was the most common haplotype among historic V. v. necator specimens and was rare in the exotic fox populations from California’s lowlands.[7][8]

The High Sierra foxes current range has been extended by recent webcam discoveries. In August, 2010, a handful were discovered fortuitously by motion sensitive cameras near Sonora Pass set up to detect rare Fisher (Martes pennanti) and Marten (Martes americana). These Sierra Nevada red foxes were photographed in the central Sierra Nevada, more than 200 miles away from Lassen Peak, and genetic analysis of saliva from bites on a bait bag was compared to museum specimens from prior to 1926, confirming their identity.[9][10] They had not been seen in the Sonora Pass area since 1925. In March 2011 a ski slope groomer on Mount Hood snapped a shot with his flip phone which spurred scientists to set up webcams in Oregon. These subsequently confirmed fox populations not only on Mount Hood, but also 200+ miles south at Crater Lake in June 2012.[11]

Although the California Central Valley red fox population had been considered non-native, genetic studies beginning in 2010 have shown that in the northern section, i.e. the Sacramento River valley, the foxes are genetically different from the introduced red fox populations to the south and in the Bay Area and should be regarded as native. There are historical accounts of these foxes living in arid valley grassland conditions quite distinct from the montane Sierra Nevada population since the 1880s.[12] Also, these native lowland California red fox are larger than the Sierra Nevada red fox.[13] The genetic evidence indicates that this new Sacramento Valley red fox is a distinct subspecies (Vulpes vulpes patwin) and that they are more closely related to the native montane fox than the introduced red fox in the rest of the state.[14] A relatively restricted and narrow hybrid zone between the lowland native and non-native foxes has been stable for several decades, despite five-fold expansion of non-native red fox populations throughout the rest of lowland and coastal California. This may be due to the foxes monogamous mating system and highly specific mate selection.[15]

Diet[edit]

A 2005 study of the then remnant population surviving on Mt. Lassen found that the foxes are nocturnal hunters whose diet was predominantly mammals, especially rodents and mule deer (Odocoileus hemionus), supplemented by birds, insects and Pinemat manzanita (Arctostaphylos nevadensis) berries as seasonally available. Lagomorphs (hares, rabbits, pikas) were virtually absent from the foxes diet.[7]

History[edit]

Upon reaching Truckey's Lake (now Donner Lake) on November 14, 1844, the Stephens-Townsend-Murphy Party, the first wagon train to cross the Sierra Nevada, left six of their eleven wagons because of difficulties getting the wagons over what would become Donner Pass. Eighteen year old Moses Schallenberger spent the winter there watching over the wagons, surviving the impassably deep snows only by trapping High Sierra foxes for food. He lived on fox which he trapped on average of one every two days, until he was rescued by Canadian-American Dennis Martin at the end of February, 1845, who showed him how to construct proper snowshoes.[16]

References[edit]

  1. ^ a b "Sierra Nevada red fox (Vulpes vulpes necator)". Sierra Forest Legacy. Retrieved 2011-04-30. 
  2. ^ Matt Weiser (2011-04-27). "Protections sought for Sierra Nevada red fox". The Modesto Bee. Retrieved 2011-11-28. 
  3. ^ Jeffrey C. Lewis, Kevin L. Sallee, Richard T. Golightly (October 1999). "Introduction and Range Expansion of Nonnative Red Foxes (Vulpes vulpes) in California". American Midland Naturalist: 372–381. JSTOR 2426786. 
  4. ^ "Sierra Nevada Red Fox to be Considered for Endangered Species Act Protection". U. S. Fish and Wildlife Service. 2011-12-30. 
  5. ^ Frank Stephens (1906). California Mammals. West Coast Publishing Co. p. 218. Retrieved 2011-04-28. 
  6. ^ J. Grinnell, J. Dixon, J. Linsdale (1930). Fur-bearing mammals of California. Berkeley, California: University of California Press. ISBN 978-0-7812-5041-2. 
  7. ^ a b c John Dixon Perrine III (Fall 2005). Ecology of Red Fox (Vulpes vulpes) in the Lassen Peak Region of California, USA (Thesis). University of California, Berkeley. Retrieved 2011-04-30. 
  8. ^ John D. Perrine, John P. Pollinger, Benjamin N. Sacks, Reginald H. Barrett, Robert K. Wayne (2007). "Genetic evidence for the persistence of the critically endangered Sierra Nevada red fox in California". Conservation Genetics: 1083–1095. Retrieved 2011-04-21. 
  9. ^ "Fox spit helped Forest Service confirm rare find". University of California, Davis. 2010-09-03. Retrieved 2011-04-30. 
  10. ^ "‘Extinct’ fox rediscovered in California". WildlifeExtra.com. 2010-09-09. Retrieved 2011-1-04-28. 
  11. ^ Carolyn Jones (2012-06-20). "Threatened California fox species found in Oregon". San Francisco Chronicle. Retrieved 2012-07-07. 
  12. ^ John D. Perrine, John P. Pollinger, Benjamin N. Sacks, Reginald H. Barrett, Robert K. Wayne (2007). "Genetic evidence for the persistence of the critically endangered Sierra Nevada red fox in California". Conservation Genetics: 1083–1095. doi:10.1007/s10592-006-9265-z. 
  13. ^ Sacks BN, Wittmer HU, Statham MJ (2010-05-30). The Native Sacramento Valley red fox. Report to the California Department of Fish and Game. (Report). pp. 49. http://www.vgl.ucdavis.edu/cdcg/documents/30May2010_FinalReport_ForDistribution_000.pdf. Retrieved 2012-07-07.
  14. ^ Benjamin N. Sacks, Mark J. Statham, John D. Perrine, Samantha M. Wisely, Keith B. Aubry (2010). "North American montane red foxes: expansion, fragmentation, and the origin of the Sacramento Valley red fox". Conservation Genetics: 523–1539. doi:10.1007/s10592-010-0053-4. 
  15. ^ Benjamin N. Sacks, Marcelle Moore, Mark J. Statham, Heiko U. Wittmer (2011). "A restricted hybrid zone between native and introduced red fox (Vulpes vulpes) populations suggests reproductive barriers and competitive exclusion". Molecular Ecology: 326–341. doi:10.1111/j.1365-294X.2010.04943.x. 
  16. ^ Moses Schallenberger (2007). Charles H. Todd, ed. Moses Schallenberger at Truckey's Lake, 1844-1845. Winters, California: 19th Century Publications. 
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Names and Taxonomy

Taxonomy

Comments: Based on genetic data, Sacks et al. (2010) expanded the scope of this subspecies. They indicated that the Sacramento Valley red fox population (named as a new subspecies V. v. patwini) is native to California and closely related to the Sierra Nevada red fox (V. v. necator).

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