Sierra Nevada Red Fox
 

(Vulpes vulpes necator):
 

A Conservation Assessment 

John D. Perrine * 

Environmental Science, Policy and Management Department
 

and
 

Museum of Vertebrate Zoology 

University of California, Berkeley
 

Lori A. Campbell**
 

USDA Forest Service 

Pacific Southwest Research Station
 

Sierra Nevada Research Center
 

Davis, California 

Gregory A. Green 

Tetra Tech EC
 

Bothell, Washington
 

Current address and contact information: 

*Primary Author: J. Perrine, Biological Sciences Department, California Polytechnic State University, San Luis 

Obispo, CA 93407-0401 jperrine@calpoly.edu 

**L. Campbell, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, CA 95616 
 

 

 

 

 

 

 

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NOTES IN PROOF
 

x	 Genetic analyses by B. Sacks and others 2010 (Conservation Genetics 11:1523-1539) indicate that the 

Sacramento Valley red fox population is native to California and is closely related to the Sierra 

Nevada red fox. They designated the Sacramento Valley red fox as a new subspecies, V. v. patwin. 

x	 In August 2010, as this document was going to press, 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. Preliminary genetic analyses conducted at UC Davis indicate that the 

fox was a Sierra Nevada red fox. Further surveys and analyses are planned. 

x	 The California Department of Fish and Game Region 1 Timber Harvest Program has established a 

Sierra Nevada red fox information portal, where many management-relevant documents can be 

downloaded as PDFs. See: https://r1.dfg.ca.gov/Portal/SierraNevadaRedFox/tabid/618/Default.aspx 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sierra Nevada Red Fox 

Conservation Assessment 

EXECUTIVE SUMMARY 

This conservation assessment provides a science-based, comprehensive assessment of the status of the 

Sierra Nevada red fox (Vulpes vulpes necator) and its habitat. It identifies and evaluates key risk factors 

affecting viability and describes general Conservation Options. The current distribution, abundance and 

population trend for Sierra Nevada red fox are uncertain, but there is little evidence of increase or 

expansion. It is unclear whether this native mountain fox persists outside of the Lassen Peak region. 

Summary of Key Findings 

Historic Range and Population Densities 

x 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). 

x Elevational range reportedly 1,200 to 3,600 m. Seldom sighted below 1,500 m and most often 

observed above 2,100 m. 

x Occurred at low densities, even in areas of high relative abundance. 

Ecology 

x	 Little studied, as are mountain red fox populations in the Cascade and Rocky Mountains. One recent 

field study in the Lassen Peak region; most other accounts based on incidental observations. 

x Small body size (average = 3.6 kg) and large seasonal home ranges (summer average = 2,300 ha). 

x Human-associated mortality is fairly well described: trapping prior to the 1974 California prohibition, 

predator eradication programs associated with livestock or timber production, historic meadow overgrazing resulting in reduced prey populations, domestic dog-mediated disease vectors, and roadkill. 

x Likely avoid coyotes (Canis latrans); niche overlap with marten (Martes americana) appears high. 

Habitat Relationships 

x	 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. 

x	 Seasonal elevational migration: summer habitat negatively associated with shrub and herbaceous 

cover; winter habitat 150-500 m lower and positively associated with forest cover comprised of large 

trees (>60 cm DBH) with >40% canopy closure. 

x Den sites described as natural cavities in talus slopes or rockslides. May use earthen dens, boulder 

piles, or even the space beneath vacant cabins, as has been described for other mountain foxes. 

x In winter, followed forested edge of openings, possibly avoiding areas where they would be exposed 

to attack by other carnivores. Ski tracks and other packed snow may facilitate winter travel. 

Potential Threats 

x	 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. 

x	 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. 

o	 Habituation and begging habits may increase risk of mortality at roads, campgrounds, etc. 

o Fish poisoning disease mediated by stocking infected fish for recreational fisheries. 

x Contact with rodenticides applied for vegetation or livestock management purposes. 

x Climate change, resulting in a loss or restriction of their boreal environment or reduced snowfall. 

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Sierra Nevada Red Fox 

Conservation Assessment 

TABLE OF CONTENTS 

INTRODUCTION 1
 

Purpose of this Assessment 1
 

How the Document will be Updated 1
 

How Agency Biologists can use this Conservation Assessment 1
 

Acknowledgements 2
 

APPROACH 2
 

Organization of the Assessment 2
 

Geographic Scope of the Assessment 3
 

Objectives 3
 

Areas of Uncertainty 3
 

Description and Taxonomy 5
 

Distribution and Population Density 8
 

ECOLOGY 14
 

Population Ecology 14
 

Mortality Factors, Survivorship Rates, and Population Structure 17
 

Habitat Relationships 18
 

Home Range and Territoriality 20
 

Activity Patterns and Dispersal 22
 

Food Habits 24
 

Community Interactions 25
 

CONSERVATION STATUS 26
 

POTENTIAL THREATS 26
 

Non-native Red Fox 27
 

Development and Recreation 28
 

Forest Management and Livestock Grazing 29
 

Climate Change 30
 

Trapping 31
 

Summary of Potential Threats 31
 

CONSERVATION CONSIDERATIONS 31
 

INVENTORY, MONITORING, AND RESEARCH NEEDS 32
 

LITERATURE CITED 34
 

PERSONAL COMMUNICATIONS 42
 

PHOTO CREDITS 42
 

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Sierra Nevada Red Fox 

Conservation Assessment 

INTRODUCTION 

Purpose of this Assessment 

One goal of the Sierra Nevada Forest Plan Amendment (SNFPA) 2001 and 2004 Records of Decision was 

to protect and recover native Sierra Nevada red fox (Vulpes vulpes necator) populations in the Sierra 

Nevada (USDA Forest Service 2001 p. 14). To accomplish this goal, the ROD commits the U.S. 

Department of Agriculture (USDA) Forest Service to completing a conservation assessment for the Sierra 

Nevada red fox in cooperation with other federal, state, and local agencies, as well as Tribal governments. 

This conservation assessment synthesizes the best available scientific information and thought concerning 

habitat relationships, population status and trends, historical and current distributions, and key threats 

potentially affecting the distribution, abundance and persistence of the Sierra Nevada red fox. Biologists 

and resource managers from the Forest Service, US Department of the Interior (USDI) National Park 

Service, USDI Fish and Wildlife Service, US Geological Survey, University of California, and California 

Department of Fish and Game, along with private research scientists, worked cooperatively to develop 

this assessment. This conservation assessment provides a scientifically sound, comprehensive assessment 

of the status of the Sierra Nevada red fox population and its habitat. It identifies and evaluates key 

threats affecting viability and describes management considerations that could form the basis of a 

strategy to conserve and recover populations throughout the range of this species. 

How the Document will be Updated 

This conservation assessment has been designed as a “living document” which will be periodically 

updated as relevant new information becomes available. All authors of this assessment, as well as 

biologists with a strong or vested interest in the Sierra Nevada red fox, will be encouraged to submit new 

publications or databases to either an ftp site, web site, or a designated document coordinator to be 

established specifically for this purpose. When sufficient new information is collected to warrant 

inclusion into the conservation assessment, it will be added as a dated addendum to the document’s 

appendix. Should the new information significantly alter views established in the original conservation 

assessment, it (as well as all other addendum information) will be added to the body text as a new 

conservation assessment addition. 

How Agency Biologists can use this Conservation Assessment 

Field biologists and managers are encouraged to use the information contained herein for project 

planning and analysis. In effects analyses, document the range of habitat associations in California, then 

focus on study results and data closest to the geographic location of the proposed project to evaluate 

effects of proposed management activities. Wherever possible, original literature should be reviewed and 

cited, rather than a summary document such as this assessment, except where such an assessment 

provides data or study comparisons to generate new information. 

The National Environmental Policy Act of 1970 (NEPA) and implementing regulations provide 

specific direction for the procedure to incorporate information by reference into analyses. For example, it 

is not sufficient to state that all information contained in a document is incorporated. A summary of 

relevant data must be prepared and included in the project evaluation document. 

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Clearly list any assumptions and limitations associated with cited research to ensure proper 

contextual use of study inferences or conclusions. When doubt exists regarding proper interpretation of 

results, readers are encouraged to contact study authors directly, or discuss projects being planned with 

respected local Sierra Nevada red fox experts. When such contact results in a “personal communication” 

citation in an analysis document, it is wise to request review of any resultant text by the expert being 

cited to ensure accuracy and supportability. 

Acknowledgements 

The authors would like to acknowledge the other members of the working group who provided their 

time and expertise toward developing this document: Reg Barrett and Tom Kucera of UC Berkeley, Rick 

Golightly of Humboldt State, Diane Macfarlane and Laurie Perrot of the Pacific Southwest Region of the 

USDA Forest Service, Mike Magnuson of Lassen Volcanic National Park, Tom Rickman of the Lassen 

National Forest, Ron Schlorff of the California Department of Fish and Game, and Jesse Wild of the US 

Fish and Wildlife Service. Keith Aubry of the USDA Forest Service, John Siperek of the California 

Department of Fish and Game, and David Graber of the National Park Service reviewed the draft 

manuscript and provided many useful comments. Ellen Jackowski of Tetra Tech EC made figure 1, Rick 

Schlexer of the USDA Forest Service made figure 3, and Kristi Fein of CDFG made figure 5. The authors 

would also like to thank Jonathan Arnold of Lassen Volcanic National Park, Les Chow of the US 

Geological Survey, and the numerous field biologists with the USDA Forest Service for providing red fox 

sighting records and other inventory data. Keith Slauson of the USDA Forest Service Pacific Southwest 

Research Station in Arcata graciously provided the cover photo. 

APPROACH 

Organization of the Assessment 

The document is organized under the following key headings: 

x Description and Taxonomy 

x Distribution and Population Density 

x Ecology 

x Conservation Status 

x Potential Threats 

x Conservation Options 

x Inventory, Monitoring, and Research Needs 

Conservation considerations in the assessment could be used to launch a conservation strategy, provide 

guidance for field biologists as they evaluate potential effects of land and resource management projects, 

and identify habitat restoration opportunities during the landscape analysis process. Multiple agencies 

could use information from the assessment to begin a coordinated species conservation effort. 

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Sierra Nevada Red Fox 

Conservation Assessment 

Geographic Scope of the Assessment 

The historical range of the Sierra Nevada red fox (Vulpes vulpes necator) included the Sierra Nevada, the 

southern Cascades in California, and the mountains of western Nevada (Grinnell and others 1937; Hall 

1981). The current range is unknown. The extent of gene flow between V. v. necator and the mountain 

red fox of Washington and Oregon (the Cascade red fox, V. v. cascadensis) is also unknown. However, 

current taxonomy and management protections differentiate the mountain red fox of California from 

those in Washington and Oregon. Hence, the geographic scope for this assessment is the area 

encompassed by the species’ historical range in California (fig. 1). This area includes the Sierra Nevada 

Framework Planning Area (SNFPA) composed of the Sierra Nevada Bioregion and Modoc Plateau, as 

well as the Shasta-Trinity and Lassen Peak areas that are outside the SNFPA but important, nonetheless, 

to the conservation of this species. 

Objectives 

Objectives for this assessment include the following: 

x Summarize current scientific knowledge and expert opinion about the status of the native red fox in 

the Sierra Nevada and southern Cascades in California. 

x Summarize current information about the ecological conditions necessary for persistence of the 

species in the Sierra Nevada and southern Cascades in California. 

x Identify and evaluate the relative importance of threats that may be affecting the species or its 

habitat. 

x Develop options for species conservation, including the rationale for conservation considerations. 

x Summarize existing research and identify key information gaps. 

Areas of Uncertainty 

The ecology of mountain red foxes in North America is poorly known. Only three comprehensive 

ecological studies have been conducted: one in the Cascade Range of Washington and Oregon (Aubry 

1983), one in Yellowstone National Park (Fuhrmann 1998), and one in the Lassen Peak region of northern 

California (Perrine 2005). Furthermore, few of the results from these studies have appeared in the peerreviewed scientific literature. The paucity of targeted scientific research on these populations is a major 

factor complicating their effective management. 

The majority of the scientific understanding of red fox ecology in North America is based upon 

research conducted in the eastern and midwestern United States (Aubry 1983) in profoundly different 

habitats than inhabited by the Sierra Nevada red fox. Some aspects of mountain red fox ecology may be 

significantly different from these other populations, but in the absence of local research, the results from 

these other populations represent the best available information on red fox ecology in North America. 

The information and conclusions in this document are based upon the best available ecological research. 

Information on montane populations is presented where available, and effort has been made to highlight 

areas of concern over the applicability of other information to the Sierra Nevada red fox. 

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Figure 1 

 

N 

A 

0 50 100 

Kilometers 

Perrine, Campbell and Green 

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Figure 1. Historical range of the Sierra Nevada red fox (V. v. necator) in California based on Grinnell 

and others (1937). 

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Sierra Nevada Red Fox 

Conservation Assessment 

Description and Taxonomy 

The red fox (Vulpes vulpes) is a small canid with an elongated snout, large ears, slender legs and body, and 

a large bushy tail with a prominent white tip (Larivière and Pasitschniak-Arts 1996). Three color morphs 

or phases have been documented: red, cross and silver/black. In the red phase, the upper body and tail 

are yellowish to reddish brown, the cheeks and underside of the throat and abdomen are white, and the 

lower extremities and ear tips are black. The cross phase is more grayish-brown, with dark guard hairs 

forming a line down the back and another across the shoulders. In the black or silver phase, the head, 

torso and tail are all black with occasional silver guard hairs. In all three color phases, the tail usually 

retains its white tip (Voigt 1987; Larivière and Pasitschniak-Arts 1996). These color morphs are 

determined genetically, but all three may occur within the same litter (Voigt 1987). In most populations, 

the red phase is the most common and the other two phases are rare. However, cross foxes may be more 

prevalent in mountainous areas (Grinnell and others 1937; Larivière and Pasitschniak-Arts 1996; Aubry 

1997). Many mountain red foxes in the United States have a distinctive grayish-blonde pelage (Bailey 

1931, 1936; Grinnell and others 1937; Aubry 1983; Crabtree 1993; Perrine 2001; Swanson and others 2005). 

In North America, adult red foxes typically weigh between 3.5 and 7.0 kg (table 1), with an 

average of 4.5 to 5.4 kg for males and 4.1 to 4.5 kg for females (Ables 1975; Voigt 1987). Mountain red fox 

seem to be slightly smaller than their lowland counterparts, possibly due to reduced productivity in their 

montane environment. A trapper interviewed by Grinnell and others (1937) noted that the typical weight 

of Sierra Nevada red fox was about 4.2 kg for males and 3.3 kg for females. In the recent Lassen Peak 

study, the male fox weighed 4.0 kg and the four females averaged 3.5 kg (Perrine 2005). In the Cascades 

of Washington, the average weight of two adult males was 4.3 kg and two adult females was 3.3 kg 

(Aubry 1983). In most populations, male foxes are about 20% heavier than females (Voigt 1987). 

The Sierra Nevada red fox, V. v. necator, is one of ten currently recognized red fox subspecies in 

North America (Hall 1981). It is one of three subspecies of “mountain red fox,” along with the foxes of 

the Cascade Range (V. v. cascadensis) and the Rocky Mountains (V. v. macroura). These three subspecies 

are morphologically similar to each other and distinct from the other subspecies in North America (Roest 

1977; Aubry 1983; Crabtree 1993). The mountain red foxes originated from the same source population, 

which was broadly distributed in the contiguous United States during the last glaciation but then 

retreated to boreal habitats in the western mountains after the glaciers receded (Aubry 1983; Aubry and 

others 2009). The other red fox populations in the United States arose from different lineages. 

The taxonomy of California’s mountain red foxes has followed a circuitous, and almost circular, 

path. Prior to 1820, North American red foxes were not taxonomically distinguished from those in 

Europe, Canis [= Vulpes] vulpes: Linnaeus 1758; also sometimes referred to as V. vulgaris (e.g., Baird 1857). 

Desmarest (1820) argued that the New World red fox constituted a distinct species, Canis [= Vulpes] fulvus. 

The three color phases were identified as separate races or subspecies: fulva for the red phase, decussatus 

for the cross phase, and argentatus for the black phase. Baird (1857) claimed that red foxes in western 

North America were distinct from those of the east, and he assigned them to V. macrourus. Merriam 

(1899) used this designation for the red foxes inhabiting California’s Mount Shasta, but revised it the 

following year, describing the Sierra Nevada red fox, V. necator, and the Cascade red fox, V. cascadensis, as 

distinct species (Merriam 1900). The type specimen of V. necator was collected in 1891 near Mount 

Whitney at 2,900 m elevation. Merriam considered the Sierra Nevada red fox to be restricted to the 

southern Sierra, while the Cascade red fox occurred throughout the Cascade Range of northern 

California, Oregon, and Washington. By 1929, the mountain red foxes were recognized as subspecies of 

the North American red fox, V. fulva (Seton 1929). Grinnell and others (1930) considered the red fox of 

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the Lassen region of northern California to be V. f. necator, not V. f. cascadensis, and they later concluded 

that their specimens supported the recognition of only a single race of mountain red fox in California 

(Grinnell and others 1937). Whether the state border represented a biologically appropriate range limit 

for V. f. necator was not addressed. The current taxonomy arrived when Churcher (1959) showed that the 

North American red fox was indeed conspecific with the Old World red fox, V. vulpes. It has been 

suggested, however, that red fox taxonomy in North America should be revised to no more than four 

subspecies, with the mountain red foxes comprising only one subspecies: V. v. macroura (Roest 1979). A 

final resolution of the taxonomy, presumably using molecular methods, remains to be conducted. 

In addition to the indigenous Sierra Nevada red fox, California is also home to multiple low 

elevation red fox populations of uncertain taxonomic status. Grinnell declined to provide a subspecies 

designation for the red foxes inhabiting the Sacramento Valley because he suspected that this population 

had likely been introduced to California by humans (Grinnell and others 1937). This conclusion was 

reinforced by Roest (1977), who found that red foxes from the Sacramento Valley were morphologically 

most similar to the Great Plains red fox (V. v. regalis). By the 1990s, the “valley fox” was no longer 

restricted to the Sacramento Valley but ranged throughout the entire Central Valley and the coastal 

regions from Marin to San Diego (Lewis and others 1999). A genetic analysis of lowland red foxes 

collected from the San Francisco Bay Area, Monterey County and near Los Angeles concluded that the 

populations in these areas likely arose from multiple introduction events from multiple source 

populations (Fitzpatrick 1999). However, a subsequent genetic analysis of lowland and montane red fox 

populations throughout California suggested that the situation may be more complicated, with the 

Sacramento Valley population possibly being native and closely related to the Sierra Nevada red fox and 

other western mountain subspecies, whereas the populations in the San Francisco Bay Area and southern 

California likely originated from outside of California and possibly outside of North America (Perrine 

and others 2007). Follow-up analyses are currently being conducted by a team led by Dr. Benjamin Sacks 

of UC Davis, and their findings will likely have profound impacts upon the taxonomic status and 

management of the various populations of lowland red fox in California. Range expansion by exotic red 

foxes and the implications for the conservation of the native Sierra Nevada red fox are discussed in more 

detail below. 

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Sierra Nevada Red Fox 

Conservation Assessment 

Table 1. Body measurements of red foxes. 

Total Length (mm) Mass, Ave. (kg) Mass, Range (kg) Sample Size Location Source 

993 3.9 3.6 - 4.0 2 subadult and 1 adult males Sierra Nevada, CA Grinnell and others 1937 a 

944 3.3 2.9 - 3.6 1 subadult and 2 adult females 

1,040 4.0 NR 1 male, possibly subadult Lassen Peak / Mineral, CA Perrine 2005

978 3.5 2.9 - 3.8 4 females, includes subadults

1,070 NR 3.6 - 5.4 3 males Mount Adams, WA Bailey 1936 

NR 4.25 4.0 - 4.5 2 adult males Mt. Rainier, WA Aubry 1983 

NR 3.3 2.7 - 3.7 2 subadult and 2 adult females 

1,080 NR NR 1 male Liberty, NM Bailey 1931

992 NR NR 1 female Taos Mountains, NM

1,015 NR 3.6 - 5.4 b 1 subadult male Wind River Mountains, WY Bailey 1936 

NR 4.0 NR not reported Yellowstone National Park Crabtree and Sheldon 1999 

NR 4.5 NR 4 adults Point Mugu, CA Klope 1983 NR 3.7 NR 5 subadults NR 5.3 4.0 - 6.1 47 males Tippecanoe County, IN Hoffman and Kirkpatrick 1954 

NR 4.2 3.3 - 5.7 52 females 

1,011 5.0 4.1 - 7.0 33 adult males Illinois and Iowa Storm and others 1976

954 4.0 3.0 - 4.7 35 adult females

1,026 4.1 c NR 37 adult males southern Ontario Voigt 1987

973 3.4 c NR 37 adult females

NR 3.1 2.9 - 3.3 21 males Thumamah Reserve, Saudi Arabia Macdonald and others 1999NR 3.0 2.8 - 3.3 20 females

NR = not reported. Unless otherwise noted, measurements at time of first capture.

a Grinnell and others (1937) also quoted a fur trapper who claimed that average weight for males and females was 4.2 and 3.3 kg, respectively.b Bailey reported that this fox weighed “about 8 to 12 pounds.”c Skinned weight. 

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Distribution and Population Density 

The red fox has the most extensive natural distribution of any terrestrial carnivore, inhabiting much of 

North America, Europe, Asia and the northern extremes of Africa (Voigt 1987; Nowak 1999). 

Additionally, the red fox was introduced to Australia around 1865, where it has flourished (Lloyd 1980). 

This extensive geographic range is largely a product of the unspecialized and adaptable nature of the red 

fox and its broad tolerances for many types of habitats and foods (Lloyd 1980). However, this 

characterization of the species contrasts starkly to that of the Sierra Nevada red fox and the other North 

American mountain subspecies, which are generally considered to have restricted distributions due to 

habitat or dietary specializations (Buskirk and Zielinski 2003). 

Within their range, red fox population densities may vary by several orders of magnitude 

depending on the carrying capacity of their habitat. Densities may range from 1 fox per 30 ha in good 

habitat to 1 fox per 4,000 ha in poor habitat (Lloyd 1980). Higher densities, up to 1 fox per 3 ha, may 

occur in urban areas due to human-subsidized resource abundance (Voigt and Macdonald 1984; Voigt 

1987). A wide variety of methods have been used to assess population densities, including standardized 

traplines, track counts, aerial census of dens, hunting and trapping harvest, bounty records, 

questionnaires, and sightings by rural mail carriers and school children (Larivière and Pasitschniak-Arts 

1996). 

Historically, the Sierra Nevada red fox occurred throughout the 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 of Trinity County (Grinnell and others 1937). Within this range, 

Grinnell and others (1937) recognized three main population centers: the Shasta/Lassen region, the high 

Sierra near Mono Lake, and near Mount Whitney. Red foxes are apparently absent from the Coast Range 

(Grinnell and others 1937; Schempf and White 1977). Although the Sierra Nevada red fox seems to range 

from 1,200 to 3,600 m in elevation, it is seldom sighted below 1,500 m and is seen most often above 2,100 

m (Grinnell and others 1937; Schempf and White 1977). 

The current distribution and population status of the Sierra Nevada red fox are uncertain (CDFG 

1996). In the decades following the publication of Grinnell and others (1937), the largest concentration of 

sightings in northern California was near Lassen Volcanic National Park, with more than one third of all 

collected records (Schempf and White 1977). The Lassen Peak region accounts for the only verified recent 

detections of mountain red fox (Kucera 1993 and 1995; Perrine and Arnold 2001; Perrine 2005). Carnivore 

surveys conducted in this area from 1992-2002 using baited camera stations detected red fox only in a 

small area within Lassen Volcanic National Park and the surrounding Lassen National Forest, at a 

median elevation of 2,000 m (range: 1,379-2,612 m) (fig. 2). A field ecology study of the Lassen red fox 

population was conducted from 1998-2002 (Perrine 2005) and the results are summarized throughout the 

“Ecology” section below. A genetic comparison of this population and other specimens collected 

throughout California concluded that the Lassen red foxes were indeed a remnant of the native Sierra 

Nevada red fox (Perrine and others 2007). 

It is unclear whether the Sierra Nevada red fox persists outside of the Lassen Peak region. 

Although most National Forests within the historic range of the Sierra Nevada red fox have recently 

conducted carnivore surveys using trackplates and remotely-triggered cameras, none but the Lassen 

National Forest has detected red fox (fig. 3). A systematic survey (Zielinski and others 2005) of the entire 

Sierra Nevada and southern Cascade region of California, utilizing a combination of track plates and 

camera stations at each sample point, did not detect red fox anywhere within the historic range of the 

Sierra Nevada red fox (fig. 4). In Sequoia and Kings Canyon National Parks, a survey for marten (Martes 

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Sierra Nevada Red Fox 

Conservation Assessment 

americana) and fisher (M. pennanti) using baited track plates and camera stations (Green 2006) and a 

survey for wolverine (Gulo gulo) using baited camera stations (Institute for Wildlife Studies 2006) both 

failed to detect red foxes. Similarly, a fisher survey using baited camera stations in Yosemite National 

Park in the early 1990s also detected no red foxes (Les Chow, U.S. Geological Survey, pers. comm.). 

Although these results are troubling, they may merely indicate that surveys targeting other carnivores, 

such as Martes, do a poor job of detecting red foxes. Since Schempf and White’s 1977 summary and 

analysis, red fox sightings have been reported throughout much of the historic range of the Sierra Nevada 

red fox (fig. 5). Biologists at Yosemite National Park have received only ten red fox sighting reports since 

1977, most of which occurred in or near Yosemite Valley (Les Chow, U.S. Geological Survey, pers. 

comm.). Unfortunately, sighting reports are notoriously inaccurate, and without a photograph or 

voucher specimen, it is impossible to confirm whether the sighting was of a red fox or some similar canid 

such as a gray fox or coyote. The last reliable sighting in the Sequoia National Park and the nearby 

Sequoia National Forest occurred in 1993 (David Graber, National Park Service, pers. comm.). A red fox 

was photographed in the winter of 1990-1991 at the Tioga Pass Resort (2,940 m) on the Inyo National 

Forest, just outside Yosemite National Park (Les Chow, U.S. Geological Survey, pers. comm.). According 

to Graber and Chow, the low number of sighting reports suggests that it is unlikely that significant red 

fox populations exist in Sequoia-Kings Canyon and Yosemite National Parks. 

The Sierra Nevada red fox likely occurs at low population densities even within areas of high 

relative abundance. Grinnell and others (1937) reported that it was “not really numerous anywhere” and 

“its numbers are relatively small even in the most favorable territory.” Trappers they interviewed 

believed that the red fox occurred at densities of about 1 per square mile (260 ha). Similarly, the density 

of Cascade red fox in Oregon is unclear (Verts and Carraway 1998). There is also some question as to 

whether the Sierra Nevada red fox is rare or just rarely seen. Grinnell and others (1937) considered it 

highly elusive, suggesting that tracks and scat may be the only evidence of its presence, while Schempf 

and White (1977) described it as “rare” throughout the Sierra Nevada. Similarly, an abundance of 

sightings is not necessarily indicative of a large local population. Most of the hundreds of red fox 

sightings reported in Lassen Volcanic National Park were due to three human-acclimated individuals 

(Perrine and Arnold 2001). 

With both total range and population density unknown, no population estimate can be calculated 

for the Sierra Nevada red fox. If calculated, such an estimate would require impractically wide 

confidence intervals to incorporate all the necessary assumptions regarding the total range and the extent 

and density of occupied habitat. 

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LNF 

LVNP 

LNF 

Figure 2. Red fox detections and sampling effort by baited camera stations on the Lassen National 

Forest (LNF) and Lassen Volcanic National Park (LVNP), 1992-2002. Red foxes were detected by 

53 of 998 camera stations. Red fox detections (dark circles) were concentrated in the highest 

elevations in the region, especially in the western portion of the park, near the town of Mineral just 

south of the park, and along the perimeter of the Caribou Wilderness east of the park. (Data from 

Perrine 2005.) 

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Sierra Nevada Red Fox 

Conservation Assessment 

Lassen 

Volcanic NP 

Figure 3. Survey effort and occurrence of red fox in the Sierra Nevada and southern Cascades by 

National Forest. Carnivore surveys were conducted using sooted track plates and remotelytriggered cameras and may have targeted species other than red fox. Red foxes were detected only 

on the Lassen National Forest. 

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Figure 4. Distribution of systematic carnivore survey locations (1996-2002) within the historical 

range (white area) of the Sierra Nevada red fox (V. v. necator). No red foxes were detected during 

these surveys. Each point represents a star-shaped array of 6 sooted track plates and 1-2 remotelytriggered cameras. (Data from Zielinski and others 2005.) 

12
 
Sierra Nevada Red Fox 

Conservation Assessment 

Figure 5. Distribution of Sierra Nevada red fox sightings reported to California Department of Fish 

and Game since 1977. 

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Perrine, Campbell and Green 

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ECOLOGY 

The red fox is one of the world’s most widespread and thoroughly studied carnivores (Lloyd 1980; Voigt 

1987). Although numerous red fox studies have been conducted in North America, the vast majority 

have addressed populations in the eastern and midwestern regions. Consequently, little is known of the 

habitat requirements, activity patterns, food habits, reproductive ecology, population density, and other 

ecological characteristics of red foxes in the mountains of the western United States (Aubry 1983 and 

1997). Published reports on these populations are largely limited to statewide or regional summaries of 

vertebrate natural history (e.g., Bailey 1931 and 1936; Grinnell and others 1937). Additional sources of 

information include trapping records, sighting reports, and reviews of museum specimens (Lewis and 

others 1995). 

Targeted ecological investigations of mountain red fox populations in the United States are 

extremely sparse, with only three studies conducted to date: a PhD dissertation addressing the red fox of 

Washington and Oregon (Aubry 1983), an MS thesis on the red fox of the northern Yellowstone region 

(Fuhrmann 1998), and a PhD dissertation on the red fox of the Lassen Peak region of northern California 

(Perrine 2005). To date, virtually none of the results from these studies have appeared in the peerreviewed scientific literature. 

Overall, the characterization of the Sierra Nevada red fox as “the least well known furbearer in 

California” (Schempf and White 1977) remains true more than three decades later. 

Population Ecology 

The red fox is predominantly monogamous (Lloyd 1980), although polygamy has been reported in a few 

instances (Voigt 1987). Females are monoestrous with mating occurring over several weeks in late winter 

and early spring, with the specific dates varying with latitude (Ables 1975; Storm and others 1976; Voigt 

1987) and probably with elevation (Samuel and Nelson 1982). The proportion of non-breeding or barren 

females varies greatly among populations, ranging from less than 5% to greater than 45%, and is 

probably a function of population density, food supply, and mortality rate (Englund 1970; Harris 1979; 

Lloyd 1980; Voigt 1987). The gestation period is 51 to 53 days, with birth occurring from March through 

May (Voigt 1987). Estimates of litter sizes vary depending on whether live pups, embryos or placental 

scars are the unit of measure. Despite this, litter sizes are relatively consistent across published studies 

(table 2), with an average of five to six pups and a maximum of 12 (Ables 1975; Samuel and Nelson 1982; 

Larivière and Pasitschniak-Arts 1996). Litters larger than 12 pups probably represent communal denning 

by more than one female. The pups weigh 70 to 120 g at birth (Storm and Ables 1966). 

The young are born in a sheltered den, usually an excavated burrow or protected cavity among 

boulders or beneath tree roots (Lloyd 1980). Red foxes may also use abandoned woodchuck / marmot 

(Marmota spp.) or badger (Taxidea taxus) burrows (Samuel and Nelson 1982). These dens may be used for 

many generations (Lloyd 1980). The pups remain in the den for their first month, and may be moved to 

other dens several times before they are six weeks old (Storm and others 1976). The pups are weaned by 

eight to 10 weeks and then may travel short distances from the den unaccompanied by a parent (Ables 

1975; Storm and others 1976). By their twelfth week, the young foxes begin to explore their parents’ 

home range during daylight. Their activity remains centered on the den site, and they remain with their 

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mother throughout the summer. Dispersal occurs in early fall when the pups are fully grown (Ables 

1975; Storm and others 1976). Both males and females are capable of breeding their first winter (Ables 

1975; Samuel and Nelson 1982), although their success rate may be lower than older adults (Lloyd 1980). 

Little is known about the reproductive biology of the Sierra Nevada red fox or other mountain 

red foxes in North America. Snow tracking records (Grinnell and others 1937; Verts and Carraway 1998) 

suggest they are probably monogamous. In California, they likely breed in mid-February and give birth 

in early April. Grinnell and others (1937) reported that Sierra Nevada red fox litters averaged six pups 

and ranged from three to nine pups. The weight of evidence behind this conclusion is unclear although 

the range apparently reflects trappers’ reports. Other sources indicate that litters of two to three pups 

may be more typical for mountain red foxes. Sighting records at Lassen Volcanic National Park include a 

single report of a mother fox and three pups near Hat Creek in August 1979, and the 1993 sightings from 

Yosemite National Park and the Sequoia National Forest were of a mother with two pups. An uncollared 

fox on Lassen Peak in 1999 raised only two pups. Three collared females in the Lassen population were 

tracked for 3-5 breeding seasons and produced no litters despite the presence of a male fox in the local 

vicinity; necropsy of one of these females confirmed her nulliparity (Perrine 2005). In 1980, Aubry (1983) 

captured and radio-collared a family group consisting of an adult male, an adult female and two female 

pups. The following year one of these pups produced her own litter of three pups, at least one of which 

died by mid-June. Neither the other female pup nor her mother reproduced in 1981. None of seven adult 

female red foxes monitored by Meia and Weber (1993) in the Swiss Jura Mountains (1,000-1,300 m) bred, 

but one had reared pups just before the study began. Bailey (1931) estimated that mountain red fox in 

New Mexico had a maximum litter size of six pups, which is the average litter size in most other 

populations. In general, red fox reproductive output is strongly correlated with local food availability 

(Voigt 1987). It is possible that limited resources prevent mountain red foxes from achieving the 

reproductive output typical of populations in more productive environments. Whatever the cause, 

mountain red foxes appear to be at the lower range of typical litter size for the species. 

Similarly, little data exist on the types of den structures used by Sierra Nevada red foxes. The 

den site of the only known reproducing female in the Lassen Peak study was never discovered or 

characterized because the fox was uncollared (Perrine 2005). Grinnell and others (1937) reported that 

Sierra Nevada red foxes did not use earthen dens, instead preferring natural cavities in rockslides or talus 

slopes; as above, this likely reflects reports from trappers. Bailey (1936) noted that Rocky Mountain red 

fox dens were located under rocks or in holes dug near rocky cover to provide refuge from coyotes. In 

New Mexico, Bailey (1931) noted a red fox den among the boulders above treeline, but also mentioned 

their “burrows,” suggesting that earthen dens were common. In Washington, Cascade red foxes used 

earthen dens, some with multiple entrances, typically located in heavily timbered stands (Aubry 1983). 

Den entrances averaged 25x25 cm, with fans of hard-packed dirt extending outward. One Cascade fox 

also denned under a vacant cabin (Aubry 1983), which has also been reported among red fox in the Rocky 

Mountains (Dirk Van Vuren, UC Davis, pers. comm.). Sierra Nevada red fox likely use whatever 

structures are available to them, whether among rocks or in the ground (Aubry 1997), but to date no 

accounts of earthen burrows in the mountains of California are known. 

15
 
Perrine, Campbell and Green 

R5-FR-010 August 2010 Table 2. Litter size estimates for red foxes. 

# Pups # Pups Litters

Average Range Examined Den Type Location Source 

2.5 2 - 3 2 1 earthen,1 under cabin Mount Rainier, WA Aubry 1983 

6 3 - 9 NR under boulders Sierra Nevada, CA Grinnell and others 1937 7 2 - 13 9 not reported Sacramento Valley, Colusa County, CA Grinnell and others 1937 

3.2 NR NR Burrows Point Mugu, Los Angeles County, CA Klope 1983 

3.6 1 - 9 12 various; mostly burrows Orange County, CA Lewis and others 1993 

6.8 a 4 - 13 30 NR Tippecanoe County, IN Hoffman and Kirkpatrick 1954 

3.8 1 - 12 175 Primarily burrows Illinois Storm and others 1976 

3.5 1 - 10 384 Primarily burrows Iowa Storm and others 1976 

4.9 NR 210 Burrows Michigan Switzenberg 1950 

4.2 a NR 574 NR North Dakota Allen 1983 

5 3 - 7 10 burrows and under buildings central Alberta, Canada Dekker 1983

4.7 NR 60 NR southern Sweden von Schantz 1984 

3.8 NR ~80 NR central Poland Goszczynski 1989 

NR = not reported.

a derived from embryo counts at necropsy.

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Mortality Factors, Survivorship Rates, and Population Structure 

Human-associated factors such as trapping, hunting and road-kills account for a significant proportion of 

red fox mortality in many populations (Storm and others 1976; Samuel and Nelson 1982; Voigt 1987; 

Larivière and Pasitschniak-Arts 1996; Verts and Carraway 1998). Populations in the Midwest sustain an 

annual harvest of tens of thousands depending on the state (Lloyd 1980). One of Aubry’s (1983) seven 

radio-collared Cascade red foxes was killed by a local trapper. Trapping and hunting likely had a 

negligible effect upon the Sierra Nevada red fox due to the low numbers taken each year. Grinnell and 

others (1937) estimated the total harvest to be about 21 individuals annually, and they did not consider 

this to be a threat to the population. From 1940 through 1959, only 135 red fox pelts were taken 

throughout California, with exotic red foxes from the lowland population comprising an increasing 

portion of the statewide harvest after 1950 (Gould 1980). After 1959, the average annual harvest from the 

mountains was only two foxes (Gray 1975). Despite the low harvest levels, state resource managers were 

concerned about any preventable sources of mortality upon a species thought to be in decline. In 

response to this concern, the California Legislature prohibited trapping and other non-scientific take of 

red fox throughout the state in 1974 (Gould 1980). The moratorium remains in effect today. It is 

unknown whether this moratorium had any substantive effect upon Sierra Nevada red fox population 

levels, but a similar prohibition has likely contributed to the persistence of mountain red fox in 

Yellowstone National Park (Buskirk 1999). 

Like many other predators in the Sierra Nevada, red fox populations probably suffered from 

predator-eradication programs associated with livestock production (Grinnell and others 1937). Sheep 

ranchers routinely placed poison in dead sheep, killing thousands of predators and scavengers. In 

addition, over-grazing of mountain meadows by livestock likely harmed Sierra Nevada red fox indirectly 

by reducing the forage available for prey species (Grinnell and others 1937). Eliminating the use of 

poisons and reducing sheep allotments at high elevations in the Sierra undoubtedly benefited Sierra 

Nevada red fox conservation, although the absolute effects can only be surmised. 

Sources of red fox mortality not directly associated with humans are poorly known (Ables 1975). 

Larger carnivores such as wolves, mountain lions, and domestic dogs may occasionally kill red foxes 

(Larivière and Pasitschniak-Arts 1996), but these events likely pose little population-level threat. A 

domestic dog killed one fox in the Lassen Park study (Perrine 2005). Golden eagles occasionally prey 

upon red foxes (e.g., Tjernberg 1981) and Grinnell and others (1937) considered them to be an important 

potential predator on the Sierra Nevada red fox. Bobcats may occasionally kill red foxes, especially 

juveniles or injured individuals (Grinnell and others 1937). Studies throughout North America have 

shown coyotes to be important competitors for red foxes, chasing them and occasionally killing them 

(Dekker 1983; Sargeant and Allen 1989). (See the “Community Interactions” section below for more 

detail.) 

Diseases and parasites can also cause significant mortality in red fox populations. Rabies and 

distemper are the two diseases most commonly associated with red foxes (Ables 1975; Samuel and 

Nelson 1982; Nowak 1999). Other diseases include parvovirus, toxoplasmosis, canine hepatitis, 

tularemia, leptospirosis, and encephalitis, but these are not believed to control population densities 

(Voigt 1987). Many kinds of parasites, ranging from ticks and fleas to nematodes, trematodes, 

heartworms, and protozoans, have been documented in red foxes (Larivière and Pasitschniak-Arts 1996). 

Sarcoptic mange, caused by a mite infection, is usually fatal to red foxes (Samuel and Nelson 1982). In 

general, little is known about the effects of disease or parasites on mountain red foxes. Grinnell and 

others (1937) made no mention of parasites or disease of red fox in the Sierra Nevada. Trematodes, 

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Perrine, Campbell and Green 

R5-FR-010 August 2010 

cestodes and nematodes have been documented in Cascade and Sierra Nevada red foxes (Aubry 1983; 

Perrine 2005). 

Although mortality rates, sex ratio, demographic structure and longevity have been examined in 

many red fox populations worldwide (Lloyd 1980), these data are derived almost exclusively from 

populations under heavy harvest pressure, which skew the results. For example, hunting and trapping 

typically take more males than females and more juveniles than older adults (Ables 1975; Lloyd 1980; 

Samuel and Nelson 1982). But more important than these biases, which may be corrected for, is the effect 

of such harvest pressure upon the population’s overall demographic structure. According to Minta and 

others (1999: 341), “Human modification in the form of fur harvest, predator control, and hunting acts as 

a nonrandom, non-compensatory form of mortality, alters other demographic processes, and may disrupt 

social organization.” Specifically, heavy hunting and trapping pressure decreases adult survival, 

shortens longevity, increases the proportion of young foxes in the age distribution, and decreases the 

male:female sex ratio (Lloyd 1980; Minta and others 1999). Therefore, demographic estimates derived 

from such populations cannot be assumed to extend to the Sierra Nevada red fox, which incurs no 

harvest pressure. No studies have calculated age-specific mortality rates, sex ratio, demographic 

structure, or longevity for Sierra Nevada, Cascade, or Rocky Mountain red foxes. 

Habitat Relationships 

Worldwide, red foxes occur in a wide variety of habitats, including deserts, tundra, mountaintops, 

woodlots, meadows, agricultural fields, pastures, and urban areas (Lloyd 1980; Voigt 1987). Within these 

habitats, red foxes tend to select areas containing a mixture of vegetative types, structures and edges, and 

they avoid areas of unbroken or homogeneous vegetation (Ables 1975). Dense forests are apparently not 

widely used (Samuel and Nelson 1982), and shrub communities may be selected in some areas (Schofield 

1960; Jones and Theberge 1982; Halpin and Bissonette 1988; Theberge and Wedeles 1989). Patterns of 

habitat selection may be complicated by weather conditions, prey availability, and interactions with 

competitors such as coyotes. 

Little is known about habitat use or preference by the Sierra Nevada red fox other than their 

habitats seem to be those typical of the high Sierra. Grinnell and others (1937) reported that the Sierra 

Nevada red fox inhabited the Hudsonian and Canadian life zones, occurring above treeline, in mountain 

meadows and talus slopes, and in the subalpine woodlands of whitebark pine (Pinus albicaulis) and 

mountain hemlock (Tsuga mertensiana). In winter they descended to lower elevations (Grinnell and others 

1937), presumably to red fir (Abies magnifica) and mixed conifer forests. Ingles (1965) described their 

habitats as the alpine fell-fields and the red fir and lodgepole pine (P. contorta) forests in the subalpine 

zone of the Sierra Nevada. Mountain red foxes in Oregon and New Mexico also occurred primarily in the 

Canadian life zone (Bailey 1931 and 1936). In Oregon, mountain red foxes were absent from areas of 

dense timber and brush to the west of the Cascade crest and from the sagebrush (Artemisia spp.) zones to 

the east (Bailey 1936). Mountain red fox likely forage for rodents in mountain meadows, openings in 

conifer stands, and among the talus slopes and exposed ridges above treeline (Bailey 1931; Grinnell and 

others 1937; Aubry 1983). 

Perrine (2005) used a combination of baited camera stations and telemetry to determine habitat 

utilization by Sierra Nevada red foxes in the Lassen region. Habitat attributes at the scale of the 

individual camera station were not analyzed statistically due to concerns about independence among the 

cameras, but several trends were evident. The distribution of red fox detections appeared more restricted 

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than for marten: red foxes were detected at fewer camera stations (53 vs 132), at slightly higher elevations 

(2,000 m median, 1,379-2,612 m range vs 1,959 m median, 1,305-2,612 m range) across a smaller 

geographic area (935 km2 vs 2,460 km2 ; 95% Minimum Convex Polygon [MCP]), and in slightly fewer 

community types (9 vs 10 California Wildlife Habitat Relationships communities). Specifically, red foxes 

were detected in barren, conifer and shrub habitats at high elevations, but not in habitats of similar 

structure (e.g., sagebrush) at lower elevations. Multivariate analysis of 260 ha (1 mi2) sampling units 

indicated that red fox detections were positively associated with elevation and highway extent (the latter 

likely due to sampling bias; see fig. 2) and negatively associated with the extent of shrub and herbaceous 

cover; in winter, detections were also positively associated with the extent of forest comprised of large 

trees (>60 cm DBH) with >40% canopy closure. In the summer, radio-collared red foxes (one male and 

three females) all selected barren habitats and avoided mid-elevation conifer, hardwood and herbaceous 

community types; shrub and high-elevation conifer communities tended to be used in proportion to their 

availability (but one fox selected shrub communities and another avoided high-elevation conifers). 

Winter habitat selection was not assessed due to uncertainty about the home range boundaries, but the 

winter home ranges were dominated by Sierran Mixed Conifer, Red Fir, Montane Chaparral and White 

Fir Forest California Wildlife Habitat Relationships (CWHR) communities. The collared foxes used a 

variety of structures as day rests. In summer, dense stands of young red fir (<5 m tall) were frequently 

used, as were spaces under large boulders amidst talus slopes, and open gaps among manzanita shrubs. 

In winter the foxes used cavities under fallen logs and trees, along with the hollows formed under the 

drooping lower boughs of snow-laden conifers. No day rests in earthen dens or dug-out cavities were 

found. Occupied day rest sites, ranked by frequency, were in barren, high-elevation conifer (Red Fir and 

Subalpine Conifer), mid-elevation conifer (White Fir, Lodgepole Pine and Sierran Mixed Conifer), and 

shrub (Montane Chaparral) communities in summer, and in mid-elevation conifer (Sierran Mixed Conifer 

and White Fir), shrub (Montane Chaparral) and Aspen communities in winter. These patterns reflect the 

seasonal elevation movement by the collared foxes, discussed in further detail below.

 Aubry (1983) conducted a radio-telemetry study of the Cascade red fox at two sites near the 

northeast corner of Mount Rainier National Park in Washington. Both sites were in mountain hemlock 

woodlands and contained extensive subalpine meadows dominated by mountain bunchgrass (Festuca 

viridula). One additional study animal was captured in the open grand fir (A. grandis) forest near the 

town of Conconully. Aubry did not provide more detailed descriptions of the habitat types, or their 

relative use, within the home ranges of his animals. 

Benson and others (2005) used snow tracks to infer the use of cover by red fox near Lassen 

Volcanic National Park. The foxes used open areas less and forest cover more than expected based on the 

availability of these habitat types. At clearings, the foxes tended to follow the forest side of the edge as 

opposed to moving straight into the openings. They also documented red foxes walking in ski and 

snowshoe tracks. These data suggest that the foxes may select areas where packed snow facilitates travel, 

and may avoid areas where they would be exposed to attack by other predators. Although sample sizes 

were low, this study represents the only published analysis of mountain red fox habitat use in California. 

Sighting reports provide the only other information of habitat use by Sierra Nevada red fox. In 

the northern Sierra Nevada, sightings have been recorded about equally in fir and mixed conifer, with 

additional sightings in mixed pine and lodgepole pine. In the southern Sierra Nevada, reports were 

predominately from mixed conifer forests with additional sightings in lodgepole pine and fir (Schempf 

and White 1977). Red fox sightings on the Lassen National Forest in winter have been in mixed conifer 

and red fir forests above 1,500 m (Tom Rickman, Lassen National Forest, pers. comm.). Sightings in 

Lassen Volcanic National Park in 2000 and 2001 were concentrated in campgrounds, parking areas and 

along the main park road, reflecting the distribution of humans and 2-3 begging red foxes (Perrine and 

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Arnold 2001). Nevertheless, habitats for these areas included mixed conifer and red fir forests, mountain 

hemlock and whitebark pine woodlands, talus slopes and mountain meadows, suggesting that begging 

behavior did not change the foxes’ principal habitat associations. 

An important additional habitat attribute for Sierra Nevada red fox populations may be 

remoteness from human presence. Trappers interviewed by Grinnell and others (1937) considered the 

Sierra Nevada red fox to be the “wildest wild creature” with “greater fear of man and his scent than all 

the other fur bearers combined.” Like the wolverine, the Sierra Nevada red fox may be extremely 

sensitive to human presence. If so, this would be a marked departure from the species’ characteristics in 

other areas, where they have thrived in human-dominated habitats. However, nothing is known of how 

Sierra Nevada red foxes respond to increased human presence or disturbance. Such interactions may be 

complex and may depend upon other ecological factors. For example, in areas where competition with 

coyotes is important, human-dominated areas can provide important refugia for red foxes (Gosselink and 

others 2003). Human residences may also provide food and denning locations. Red foxes in the Lassen 

area of California clearly use roads as movement corridors to facilitate both daily and seasonal 

movements, with some individuals foraging along the roads as well (Perrine 2005). Several foxes in the 

Lassen area became quite acclimated to humans, posing problems at some campgrounds and parking 

areas (Perrine 2005). 

In the absence of demographic data, habitat associations must be interpreted with care. Densely 

inhabited habitats may not be preferred or even sufficient to sustain their populations (Van Horne 1983; 

Pulliam 1988). In some areas, competition with coyotes has relegated red foxes to sub-optimal habitats 

(Harrison and others 1989; Fuller and Harrison 2006). Under such conditions, optimal habitats may 

appear unused and sink habitats may appear preferred. Habitat-specific survival and fecundity rates are 

necessary to accurately assess habitat relationships and requirements (Garshelis 2000). Unfortunately, 

such data are unavailable for mountain red foxes. 

Home Range and Territoriality 

Globally, red fox home range sizes vary widely, from 10 ha to 3,400 ha (table 3), depending on habitat 

type and food availability (Ables 1975; Samuel and Nelson 1982; Voigt 1987). For example, red foxes in 

the urban areas of Bristol and Oxfordshire, UK, had among the smallest home ranges in the literature, 45 

ha on average, presumably due to abundant resources (Harris 1980; Voigt and Macdonald 1984). In 

Wisconsin, mean MCP was 141 ha (range: 71-220 ha) but the foxes were tracked for only 11-148 days 

(Ables 1969). Exotic red foxes in Orange County, California had average MCP home ranges of 427 ha 

(Lewis and others 1993). Family groups in Minnesota occupied areas that were ǂ960 ha (Storm and others 

1976). In Ontario, home ranges were 900 ha (range: 500-2,000 ha), typical of most studies in the 

agricultural areas of central and eastern North America (Voigt and Tinline 1980; Voigt 1987). Red foxes at 

high latitudes have the largest home ranges, reflecting reduced habitat productivity due to the short 

growing season. Red foxes in eastern Maine had mean annual MCPs of 1,470 ha (range: 600-2,750 ha; 

Harrison and others 1989). Summer home ranges for red foxes in the tundra of northwest British 

Columbia averaged 1,611 ha (range: 277-3,420 ha; Jones and Theberge 1982), and winter home ranges in 

Lapland were 3,000 to 5,000 ha (Heptner and others 1998). Note that all these studies used the MCP 

method, which is comparable among studies; the size of home ranges and core areas constructed using 

fixed or adaptive kernel methods are not (Kernohan and others 2001). Within a habitat, home ranges 

often increase in winter due to decreased prey availability or increased energetic demands associated 

with reproduction (Ables 1975; Aubry 1983). Breeding females may have smaller home ranges in the 

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Sierra Nevada Red Fox 

Conservation Assessment 

weeks following parturition, when they remain in the den nursing the pups (Ables 1975; Samuel and 

Nelson 1982). Adult red foxes typically occupy the same home range for most of their life (Ables 1975). 

Sierra Nevada red foxes in the Lassen Peak region had extremely large seasonal home ranges and 

a pronounced elevational migration. Perrine (2005) conducted radio-telemetry on five red foxes from 

1998-2002, with individual animals tracked from three to 60 months. In the summer, the collared foxes 

(one male and three females) occupied the western half of Lassen Volcanic National Park and had an 

average home range size of 2,323 ha, with individual HRs ranging from 262 to 6,981 ha (95% MCP, based 

on >20 locations). Detection elevations ranged from 1,755 to 3,130 m, with an average of 2,416 m across 

the four foxes. In winter, the foxes descended to lower elevations, usually several km south of their 

summer ranges. Winter home ranges for five collared foxes (one male, four females) averaged 3,131 ha, 

with individual HRs ranging from 326 to 6,375 m. However, the true winter HR sizes may significantly 

larger, as telemetry was biased by the difficulty of accessing the higher elevations on foot due to the 

heavy snowfall in the area (Perrine 2005). Aerial telemetry locations were less biased, and indicated that 

winter HRs were 439 m lower than summer locations, on average. The descent to the winter range 

seemed to coincide with the advent of heavy snowfalls at high elevations. Grinnell and others (1937) 

reported a similar seasonal elevational movement for Sierra Nevada red foxes, with the winter range 

being 150-300 m lower than the summer range. Grinnell and Storer (1924: 77) described a captured red 

fox from Big Meadows, near Yosemite, which they speculated may have been driven to lower elevations 

by unusually severe winter weather. The large home ranges observed in the Lassen population are near 

the upper extreme of the values in the literature, and suggest that food, rest sites or other important 

resources occur at low densities or are widely dispersed even in summer. The elevational shift to lower 

elevations suggests that these resources may become unavailable once the heavy snows begin on the 

summer range. Together, these factors may limit the local population size to less than might otherwise be 

expected (Perrine 2005). 

Aubry (1983) tracked a total of seven radio-collared Cascade red foxes during three summers and 

one winter. Summer home ranges (100% MCP, n=10) averaged 235 ha and ranged from 26 to 1,166 ha. 

Excluding the largest home range as a possible outlier, the revised average was 132 ha. Winter home 

ranges (n=3) averaged 193 ha and ranged from 91 to 308 ha. His study animals did not exhibit any 

seasonal elevation shifts in habitat use, although their home range size increased in winter. The HR 

values for Cascade red foxes are similar to the 200 ha average reported for red fox home ranges in 

Yellowstone National Park (Crabtree and Sheldon 1999), and for the 260 ha (1 mi2) average estimated for 

Sierra Nevada red fox (Grinnell and others 1937). However, Aubry’s home ranges may be 

underestimates. His seasonal sample sizes were small (11-34 locations per fox), so the MCPs may not 

have reached their asymptotes. Furthermore, Aubry conducted his telemetry during daylight, when the 

foxes were presumably resting. Since red foxes generally forage at night (Voigt 1987), omitting nocturnal 

locations can dramatically reduce home range estimates (Smith and others 1981). 

Foxes use urine and other scents to delineate the boundaries of their territories, and interlopers 

may be chased or attacked (Samuel and Nelson 1982; Voigt 1987). Ables (1975) questioned whether red 

fox exhibited territorial behavior, but noted that the existence of non-overlapping home ranges was 

powerful evidence. Voigt (1987) concluded that home ranges are defended as territories, but that 

substantial overlap also occurred. Such overlap is likely to be more extensive in populations with large 

home ranges, as individuals have reduced opportunity for border defense (Goszczynski 2002). Perrine 

(2005) did not conduct any analyses of home range overlap or discuss any interactions among 

neighboring foxes in the Lassen Peak population of Sierra Nevada red fox. The home ranges of the two 

foxes in Aubry’s Yakima Park study area (in Mount Rainier National Park) overlapped substantially, but 

these individuals were never located near one another. Aubry also captured a family group of four foxes 

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R5-FR-010 August 2010 

(an adult male, a lactating female, and two juvenile females) in his Crystal Mountain study area (near Mt. 

Rainier). Their home ranges overlapped as well, and the overlap zone included the likely natal den. 

Activity Patterns and Dispersal 

Red foxes are primarily nocturnal or crepuscular (Ables 1975; Voigt 1987). For example, foxes in Illinois 

became active up to two hours before dark and remained active until up to four hours after dawn (Storm 

1965). Daytime foraging, however, is not uncommon, and may be more prominent during the winter 

(Ables 1975; Voigt 1987). A fox’s travels during a typical day rarely exceed 10 km (Voigt 1987). Most 

areas within the home range are visited within a two-week period, with the fox often visiting the same 

area on several consecutive evenings (Voigt 1987). Telemetry and camera stations indicate that Sierra 

Nevada red foxes do little foraging during daylight hours, with most activity occurring between dusk 

and dawn (Perrine 2005). Similarly, Cascade red foxes were active throughout the day, with activity 

peaks in the early morning and late evening (Aubry 1983). Aubry did not conduct telemetry at night, so 

foraging behavior cannot be assessed. Daily movements by Sierra Nevada red foxes were comparable to 

those in most other populations: virtually all independent telemetry locations obtained less than 24 hours 

apart were within 10 km linear distance (Perrine 2005). 

Information on the dispersal of mountain red foxes is extremely limited. Of the two juvenile 

females collared by Aubry (1983), one dispersed approximately 8 km before birthing a litter of pups, and 

the other remained near her original natal den. In general, young red foxes disperse between August and 

March, with the peak in October and November (Voigt 1987). Dispersal apparently occurs in “easy 

stages” rather than a tightly coordinated exodus (Ables 1975), and does not seem to be triggered by food 

limitations (Storm and others 1976). Juvenile males are more likely to disperse than females and 

generally travel two to three times as far (20-30 km for males vs 10-15 for females; Ables 1975; Storm and 

others 1976; Lloyd 1980; Voigt 1987). Foxes not dispersing their first season likely do so the following 

year (Storm and others 1976). Since dispersing individuals must cross occupied home ranges, dispersal 

distance is positively correlated with home range size. Therefore, poorer habitats are associated with 

longer dispersal distances (Voigt 1987). Distances may vary widely even within the same habitat type or 

population, and may range from 2 to 400 km (Ables 1975; Lloyd 1980). Dispersal distances greater than 

200 km for males and 100 km for females have been documented in the Midwest (Storm and others 1976). 

One subadult male marked in Wisconsin was recovered nearly 400 km away in Indiana the following 

year, but this was considered exceptional (Ables 1965). Most recoveries of marked juveniles are within 16 

km of their birthplace; however, such recoveries may underestimate dispersal distance because the 

individuals may not have reached their final destination at the time of capture (Ables 1975). 

22
 
Sierra Nevada Red Fox 

Conservation Assessment 

Table 3. Home range sizes (in ha) estimated for red foxes. (MCP = minimum convex polygon.) 

Average Range (ha) Method Comments Location Source 

191 132 – 282 seasonal 95% MCP 2 males Mount Rainier, WA Aubry 1983 

125 a 26 – 308 4 females 

311 104 - 440 NR 2 females, 1 male Point Mugu, Los Angeles County, CA Klope 1983 

435 NR MCP 11 adult males Orange County, CA Lewis and others 1993 

415 NR 8 adult females 

197 b 116 - 353 seasonal MCP 7 adult females, 2 adult males Jura Mountains, Switzerland Weber and Meia 1996 

852 NR 95% MCP 31 adults Thumamah Reserve, Saudi Arabia Macdonald and others 1999 131 63 - 270 MCP 9 males Jervis Bay, New South Wales, Australia Meek and Saunders 2000 

132 60 - 210 5 females 

124 19 - 233 95% MCP 3 males, 2 females Maremma Natural Park, Italy Cavallini and Lovari 1994 

1,611 277 - 3420 MCP 4 males, 3 females Northwestern British Columbia, Canada Jones and Theberge 1982 

141 c 71 - 220 MCP 2 males, 5 females Madison, WI Ables 1969 

1,990 NR MCP 4 adults western Maine Major and Sherburne 1987

 503 d 224 - 1087 seasonal 95% adaptive kernel 9 adults, summer east-central Illinois Gosselink and others 2003 

1,404 d 246 - 3179 8 adults, winter 

1,470 600 - 2750 annual MCP 3 males, 3 females eastern Maine Harrison and others 1989 

1,190 e 330 - 2120 annual MCP 15 families North Dakota Sargeant and others 1987 

NOTE: Home range size can vary widely depending on the method used.

a not including 1 female on a different study site with a summer home range of 1,165.5 ha.b not including 1 female with a home range of 3,383 ha.c not including 1 male with a home range of 931 ha.d median.e family home ranges

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Food Habits 

Probably no facet of red fox ecology has been more thoroughly studied than their food habits. More than 

a hundred studies have been conducted on red fox dietary patterns throughout a wide range of countries 

and habitats (Ables 1975; Lockie 1977). The overall result is a general characterization of red foxes as 

opportunistic predators and scavengers that eat a wide variety of foods depending on their seasonal 

availability. Small and medium-sized mammals usually dominate the diet, with birds, insects, 

invertebrates, fruit, carrion, garbage and other foods important seasonally (Ables 1975; Lloyd 1980; 

Samuel and Nelson 1982; Larivière and Pasitschniak-Arts 1996; Verts and Carraway 1998; Nowak 1999). 

Food preferences independent of availability are poorly known, except that red foxes appear to prefer 

voles (Microtus spp.) and avoid shrews and moles (Macdonald 1977; Lloyd 1980). 

Grinnell and others (1937) documented mice (probably Peromyscus sp. or Microtus sp.), bushytailed woodrats (Neotoma cinerea), Douglas squirrels (Tamiasciurus douglasii), Belding’s ground squirrels 

(Spermophilus beldingi), chipmunks (Tamias sp.), and white-tailed jackrabbits (Lepus townsendii) in Sierra 

Nevada red fox scats. Additionally, they observed or found evidence of red foxes hunting goldenmantled ground squirrels (S. lateralis), voles (Microtus sp.) and snowshoe hares (L. americanus), and noted 

that the foxes likely also consumed hairy woodpeckers (Picoides villosus), Williamson’s sapsuckers 

(Sphyrapicus thyroideus), Clark’s nutcrackers (Nucifraga columbiana), mountain chickadees (Poecile gambeli), 

blue grouse (Dendragapus obscurus), flying squirrels (Glaucomys sabrinus), pikas (Ochotona princeps), and 

weasels (Mustela spp.), and scavenged livestock carcasses. 

The diet of foxes in the Lassen region was dominated by rodents year-round, with pocket 

gophers (Thomomys monticola), mice (Peromyscus sp.), voles (Microtus sp.) and ground squirrels 

(Spermophilus sp.) being particularly prominent (Perrine 2005). Mule deer (Odocoileus hemionus) carrion 

was also frequently consumed, particularly in winter, and insectivore remains were more common than 

in most other studies. Arthropods were prevalent in summer scats and manzanita (Arctostaphylos 

nevadensis) berries were common in autumn, and birds and garbage were taken incidentally throughout 

the year. Lagomorph remains were virtually absent from the scats of Lassen red foxes, marten, and 

coyotes, suggesting that local populations may be low. 

Aubry (1983) found that Cascade red foxes in Washington had a summer diet consisting of 

pocket gophers (Thomomys talpoides), red-backed voles (Clethrionomys gapperi), heather voles (Phenacomys 

intermedius), and other rodents, along with fruit, insects, birds, grass, and garbage. Their winter diet was 

narrower, consisting largely of snowshoe hares, red-backed voles, pocket gophers, and other mammals, 

with some birds and garbage taken opportunistically. 

Pocket gophers clearly seem to be an important food for mountain red foxes. Bailey (1931 and 

1936) also noted that pocket gophers were common in mountain red fox scats from both New Mexico and 

Oregon. The fact that gophers were prominent in the Cascade red fox diet but not abundant in the study 

site led Aubry (1983) to suggest that the foxes might be specialists on this particular prey. In Lassen, 

gophers seemed to be widespread throughout the foxes’ summer range, so it was unclear whether they 

were being taken disproportionate to their availability (Perrine 2005). However, the importance of 

gophers as a summer and autumn food, their inaccessibility once heavy snows begin, and the apparent 

paucity of snowshoe hares and other lagomorphs may be factors behind the seasonal elevational 

movements of the Lassen red foxes (Perrine 2005). 

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Sierra Nevada Red Fox 

Conservation Assessment 

Community Interactions 

As noted in the “Mortality Factors” section above, Sierra Nevada red foxes may be chased, attacked, or 

killed by a variety of other species, including golden eagles, bobcats, mountain lions, and coyotes 

(Grinnell and others 1937). Of these species, coyotes likely have the most significant impact on red fox 

distribution and abundance, due to their role as both a predator and a competitor. Antagonism by 

coyotes toward red fox has been documented in numerous populations throughout North America. Red 

foxes appear to minimize such interactions by avoiding areas occupied by coyotes (Dekker 1983; Voigt 

and Earle 1983; Major and Sherburne 1987; Sargeant and others 1987; Harrison and others 1989; Gosselink 

and others 2003). Bailey (1936) noted that Cascade red foxes were found primarily in areas where coyotes 

were uncommon, and that the red foxes lived and bred near rocky areas that provided retreats and cover 

from coyotes. Likewise, Aubry (1983) hypothesized that predation by and competition with coyotes 

might partially explain the distribution of Cascade foxes and their failure to expand their range. Perrine 

(2005) used baited camera stations to assess the overlap between Sierra Nevada red foxes and coyotes in 

the Lassen region. Aside from a general trend of more coyote detections at lower elevations and more 

red fox detections at higher elevations, his results were inconclusive; camera stations are a poor method 

of detecting coyotes because territory-holding individuals may detect and avoid them (Sequin and others 

2003). In Yellowstone National Park, red fox home ranges did not coincide with coyote core areas, and 

red foxes were active at night while coyotes were primarily diurnal or crepuscular (Fuhrmann 1998; 

Crabtree and Sheldon 1999). The reintroduction of wolves (Canis lupus) to Yellowstone may benefit red 

foxes by reducing coyote populations (Fuhrmann 1998). Coyotes occur throughout the historical range of 

the Sierra Nevada red fox (Zeiner and others 1990), although their use of high-elevation habitats is poorly 

studied. In most populations, interference competition by coyotes causes fine-scale resource partitioning 

between the two canid species, not extirpation of the red fox population (Crabtree and Sheldon 1999). In 

areas with an elevational gradient, such partitioning can result in elevational stratification, with coyotes 

at lower elevations restricting the red foxes to the higher elevations (Dekker 1989; Fuller and Harrison 

2006). However, the presence of coyotes and other large carnivores may not be exclusively detrimental to 

red foxes. In particular, red foxes may benefit from scavenging carcasses of prey killed by larger 

carnivores, especially during winter (Buskirk 1999). 

Competitive interactions with smaller carnivores are more difficult to address. Gray foxes 

(Urocyon cinereoargenteus) may dominate red foxes in some areas (Voigt 1987), but gray foxes do not seem 

to be common at the elevations occupied by the Sierra Nevada red fox. Nevertheless, dispersing gray 

foxes could possibly transfer diseases or parasites into the Sierra Nevada red fox population. Bobcats are 

not generally considered a major competitor with red foxes (Major and Sherburne 1987). Marten likely 

have the most extensive range overlap with the Sierra Nevada red fox (Grinnell and others 1937; Zeiner 

and others 1990; Kucera and others 1995), potentially leading to competitive interactions between these 

species. In Europe and Scandinavia, red foxes have significant habitat and dietary overlap with stone 

martens (Martes foina) and pine martens (M. martes) (Serafini and Lovari 1993; Padial and others 2002). 

Occasional predation of martens by red foxes, and increases in pine marten numbers following a decline 

in red foxes, suggest that these species may have competitive interactions (Lindstrom and others 1995; 

Overskaug 2000). Avoidance of red foxes has been hypothesized to have a major influence upon marten 

habitat utilization (Drew and Bissonette 1997). However, little research has been conducted on 

competitive interactions between red fox and marten in North America despite the overlap in their 

ranges. In the Lassen region, red foxes and martens had extensive overlap in their habitat utilization, 

activity time and diet, but there was no evidence of competitive exclusion and the resources they shared 

did not appear to be limiting (Perrine 2005). 

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CONSERVATION STATUS 

In 1974, the California state legislature prohibited trapping and other non-scientific take of red foxes 

throughout the state due to concern over apparent declines of the native mountain population (Gould 

1980). The Sierra Nevada red fox was listed as a State Threatened species in 1980. It is not listed under 

the federal Endangered Species Act but is considered a Sensitive Species by the Pacific Southwest Region 

of the USDA Forest Service. The California Department of Fish and Game has classified it as “extremely 

endangered,” with <6 viable occurrences or <1,000 individuals or <2,000 acres (810 hectares) of occupied 

habitat (CDFG 2004). No estimates of population size or trend are available. 

Perrine and others (2007) conducted a genetic comparison of nine specimens from the Lassen 

Peak population (collected from 1998-2002) and 22 museum specimens from throughout the historic 

range of the Sierra Nevada red fox (collected from 1911-1941). The individuals in the modern Lassen 

population had only one mitochondrial DNA haplotype, although an additional four haplotypes were 

present in the historic specimens. This result suggests that the Lassen foxes comprise a small, isolated 

remnant population that has lost much of its genetic diversity. Follow-up analyses are underway to see if 

nuclear markers show a similar pattern. These analyses are hindered by the lack of any additional 

modern specimens from the historic range of the Sierra Nevada red fox. 

The Sierra Nevada red fox is the only major population of red foxes in North America that is of 

conservation concern due to apparently declining populations (Nowak 1999). The actual trend is 

unknown, due largely to the difficulty in surveying such a rare species in such inhospitable terrain. 

Grinnell and others (1937) believed that the population was naturally dynamic, with some portions 

increasing while others decreased. Trappers they interviewed believed that the Sierra Nevada red fox 

was increasing locally. However, 40 years later, Schempf and White (1977) concluded that the Sierra 

Nevada red fox was at best maintaining low population levels, and was perhaps declining. Of the six 

furbearers they reviewed (red fox, wolverine, fisher, river otter [Lutra canadensis], marten, and ringtail 

[Bassariscus astutus]), only the red fox did not seem to be increasing in abundance. Trends since 1977, 

however, are unknown. 

The relatively low number and localized distribution of recent Sierra Nevada red fox sightings 

suggests a small, restricted, and possibly declining population (Schempf and White 1977; CDFG 1996). A 

recent assessment concluded that the Sierra Nevada red fox “remains one of the few State-listed animals 

for which there is no information on current status other than periodic sightings filed mostly by 

inexperienced observers” (CDFG 1996). 

POTENTIAL THREATS 

A threat is a factor that adversely affects individuals, populations, habitat, prey or other essential 

resources. Such factors may be of anthropogenic or non-anthropogenic origin. The paucity of available 

data on Sierra Nevada red fox ecology makes threats difficult to assess and prevents cause-and-effect 

relationships from being documented. Likewise, the ecological factors that may limit Sierra Nevada red 

fox distribution, fecundity, and survival are unknown. In fact, the absence of reliable data upon which to 

base management decisions has itself been described as a threat to the population (CDFG 1987). 

Therefore, this threat assessment is largely speculative, and additional research is needed to assess the 

relative importance of the potential threats listed below. 

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Sierra Nevada Red Fox 

Conservation Assessment 

Non-native Red Fox 

One of the greatest threats to the Sierra Nevada red fox may be the non-native red fox, also known as the 

lowland or valley fox. Low-elevation red foxes in California were first recorded from the northern 

Sacramento Valley, where they occurred from Sutter County north to Shasta County at elevations below 

100 m (Grinnell and others 1937). Grinnell and others (1937) surmised that this population likely had 

been “planted there by man” prior to 1890, but expressed no concern about their possible impacts upon 

the native Sierra Nevada red fox, as the lowland population was “very restricted [and] evidently wholly 

cut off from the population of the Sierra Nevada.” In subsequent decades, however, the range of the 

lowland red foxes increased dramatically. By the 1990s, valley foxes had been documented in at least 36 

counties in California (Lewis and others 1993). In addition to the Sacramento Valley, their current range 

includes virtually the entire area between the San Francisco Bay and San Diego, extending eastward 

through the San Joaquin Valley to the Sierra Nevada foothills (Lewis and others 1999). Red foxes 

escaping from commercial fur farms may have contributed to the sudden expansion of the valley fox 

range. From the 1920s through the 1940s, nearly 125 fur farms were operational throughout California, 

primarily along the northern coast, the mid-state, and near Los Angeles (Lewis and others 1999). While 

most of these farms were at lower elevations, several were located within the historical range of the Sierra 

Nevada red fox, and others were within dispersal distance (Lewis and others 1995). These factors have 

raised concerns that the lowland red fox may have invaded the historic range of the Sierra Nevada red 

fox (Lewis and others 1995, 1999). These concerns are compounded by the fact that morphological 

characteristics alone cannot reliably diagnose an individual red fox as native or exotic (Roest 1977). 

A recent genetic analysis (Perrine and others 2007) found no evidence that exotic red foxes had 

invaded the Lassen Peak population. The Lassen population had the same mitochondrial haplotype that 

was most abundant in museum specimens collected prior to 1940 throughout the range of the Sierra 

Nevada red fox. This haplotype was absent from the lowland populations in the San Francisco Bay Area 

and southern California, suggesting little genetic contact. Surprisingly, these lowland populations were 

also quite different from the red foxes in the Sacramento Valley, which were more similar to the modern 

and historic mountain specimens. Although the Sacramento Valley population shared haplotypes with 

the montane populations, differences in haplotype frequencies indicated little gene flow. These results 

indicate that the dramatic range increase in the lowland red fox since the 1950s was not due to expansion 

of the Sacramento Valley population. This finding is consistent with Fitzpatrick’s (1999) genetic analysis 

of specimens collected from near San Francisco, Monterey and Los Angeles, which concluded that these 

populations had originated from multiple anthropogenic introductions from multiple source populations. 

The rapid range expansion of red foxes in southern California is consistent with their exotic origins 

(Lewis and others 1999). It remains unclear whether they have expanded into the Sierra, but the threat 

cannot be discounted. 

Exotic red foxes could have a number of detrimental effects upon the native Sierra Nevada red 

fox (Lewis and others 1995). Interbreeding could cause genetic swamping of the native, locally-adapted 

genotype, producing hybrids of reduced fitness. Also, the exotic red fox might simply exclude or outcompete the native fox, or transmit harmful diseases and parasites to the native Sierra Nevada red fox 

(Lewis and others 1995). On the other hand, exotic red foxes may not be able to persist in the extreme 

habitats of the Sierra Nevada and Cascade Range, especially in competition with a locally-adapted native 

genotype. Aubry (1984) hypothesized that physiological or behavioral limitations restricted introduced 

foxes to lower elevations in Washington and similarly restricted the native Cascade red foxes to the 

higher elevations. 

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Development and Recreation 

Road construction and increased human settlement in the Sierra Nevada might facilitate the dispersal of 

non-native red foxes into the historic range of the Sierra Nevada red fox, by providing access to areas 

previously unavailable to the exotic foxes. Although Sierra Nevada red foxes use roads and areas of 

packed snow as travel corridors, these features may also facilitate the expansion of coyotes and exotic red 

foxes into Sierra Nevada red fox habitat. In Washington, a band of dense forest on the west side of the 

Cascades separates the introduced and native fox populations (Aubry 1983 and 1984). Conversion of 

these forested habitats might ultimately be detrimental to the native red fox, as it might favor coyotes and 

exotic red foxes, both of which are potential competitors. Although the tolerance of Sierra Nevada red 

fox to the presence of humans is a topic of debate, it is clear that the non-native red foxes thrive in 

human-altered environments (Lewis and others 1999; Kamler and Ballard 2002). In addition, 

development within the range of Sierra Nevada red fox poses a threat to the species through an increased 

risk of predation from domestic pets, disease transmission, automobile collisions and other humanwildlife conflicts. 

Risks from recreation are primarily associated with developments such as ski areas, snow parks, 

campgrounds, and picnic areas. In campgrounds without bear boxes, where campers’ food and trash are 

more accessible, red foxes can develop begging habits and thereby increase the possibility for conflict 

with humans. Red foxes are intelligent and can quickly become acclimated to human handouts. They 

may be particularly susceptible in mountainous regions where natural productivity is low and winter 

food is scarce. Begging foxes have been a periodic problem in Lassen Volcanic National Park and the 

adjacent Lassen National Forest (Perrine and Arnold 2001; Perrine 2005). One of Aubry’s study animals 

became a beggar at a town near his study site (Aubry 1983) and begging foxes have been reported from 

subalpine parks in Hokkaido, Japan (Tsukada 1997) and New South Wales, Australia (Bubela and others 

1998). Domestic dogs in recreation areas may also have an impact on Sierra Nevada red foxes by chasing 

or harming them or by transmitting diseases such as canine distemper, rabies, and sarcoptic mange 

(Ables 1975; Samuel and Nelson 1982; Lewis and others 1993). Educating the public to avoid interactions 

with wildlife and to properly control their dogs could reduce these threats but cannot eliminate them 

entirely. Fortunately, these threats are unlikely to affect entire red fox populations, although virulent 

diseases could have a major impact, especially on a small population with reduced genetic diversity. 

Fish stocking for recreation may represent another threat. Neorickettsia helminthoeca is a rickettsial 

organism present in some trout and salmon stocks. Consumption of infected fish can cause salmon 

poisoning disease (SPD), which is typically fatal for dogs, foxes and other canids (Gorham and Foreyt 

1990). The rickettsial infection is known to occur in wild populations of salmonid fish in northern 

California, Oregon and Washington, but may be spread beyond these areas via translocations from 

infected hatchery populations (Hedrick and others 1990; Mack and others 1990). The trematode host of 

N. helmintoeca has been detected in at least three state hatcheries and four private farms in northern 

California, and rickettsia-infected fish from at least one of these sites were used to stock portions of the 

Truckee River Basin (Hedrick and others 1990). Red foxes could be exposed to SPD by scavenging offal 

from recreational fishing or due to the failure of aerial stocking to hit the targeted lake. Additionally, 

dead salmonids from hatcheries have been used as bait for photographic surveys of wild carnivores in 

some areas (Tom Rickman, Lassen National Forest, pers. comm.). Because of the documented occurrence 

of infected salmonids in both natural and hatchery fish populations within the range of Sierra Nevada red 

fox, and the high mortality rate of SPD in canids, further investigation of this potential threat, including 

possible routes of infection, seems warranted. 

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Sierra Nevada Red Fox 

Conservation Assessment 

Forest Management and Livestock Grazing 

It is difficult to evaluate the potential impacts that past and present forest management practices have 

had on the Sierra Nevada red fox, as little information exists on their habitat associations and movement 

patterns. The available information suggests that Sierra Nevada red foxes require a composite of habitat 

types including open forest, meadows, and subalpine fell fields. Clearly, conservation and recovery of 

the Sierra Nevada red fox will require the retention of sufficient habitat for red fox and their prey, along 

with sufficient habitat connectivity throughout its range. Forest management practices, including fire 

suppression activities and livestock grazing, may have significant impacts on habitat suitability and 

connectivity for the Sierra Nevada red fox and its prey. 

Grinnell and others (1937) considered the overgrazing of alpine meadows by sheep to be “the 

greatest menace to the productivity” of the Sierra Nevada red fox, due to the reduction of forage available 

for prey species, ostensibly grassland species such as meadow voles (Microtus sp.). Similarly, decades of 

fire suppression in the Sierra Nevada have allowed tree cover to encroach on meadow and riparian areas, 

reducing herbaceous cover for prey and reducing meadow extent. The direct impacts upon the Sierra 

Nevada red fox are unclear, however. Current livestock grazing does not occur at the intensity of the 

past (Ratliff 1985; Menke and others 1996), and some rodent populations (e.g., pocket gophers and 

Belding ground squirrel) may actually increase due to grazing practices (Ratliff 1985). Furthermore, 

increasing the amount of tree cover in meadow habitats can increase the number of chipmunks and tree 

squirrels using these habitats (Cain 2001). Consequently, livestock grazing and fire suppression may 

simply shift prey abundance from meadow voles to gophers and squirrels, all of which may be important 

components of the red fox diet (Bailey 1931 and 1936; Grinnell and others 1937; Aubry 1983; Perrine 

2005). The extent to which the Sierra Nevada red fox can adapt to such shifts in prey abundance is 

unknown. 

Sierra Nevada red foxes likely occupy elevations higher than most commercial timber extraction 

activities. However, they descend to mid-elevation forested areas in winter (Grinnell and others 1937; 

Perrine 2005). Reduction in forest density and canopy coverage could result in local increases in prey 

species such as Microtus, Peromyscus and Thomomys, possibly benefiting red foxes. However, as 

mentioned above, such structural changes could also cause increased use by coyotes and facilitate 

invasion by lowland red foxes, resulting in threats to the Sierra Nevada red fox. Snow tracks of Sierra 

Nevada red fox in the Lassen area indicated that they avoided openings in the forests, perhaps to 

minimize interactions with potential predators or competitors (Benson and others 2005). 

The use of toxins such as strychnine in grazing and forest management practices could harm 

Sierra Nevada red foxes by reducing prey populations and by the risk of secondary exposure to the toxins 

themselves. The widespread and indiscriminant use of strychnine to control predator populations on 

grazing lands has largely been outlawed, especially in California. However, rodenticides are still widely 

used on public and private lands to protect vegetation and livestock and to control plague. The most 

widely used chemicals appear to be strychnine, used for pocket gopher control, and diphacinone, used to 

control ground squirrel and chipmunk populations primarily in response to plague outbreaks in human 

recreation areas (Dave Bakke, USDA Forest Service, pers. comm.). Historically, the widespread aboveground application of strychnine for rodent control caused extensive mortality of non-target species, 

including canids (Linsdale 1931 and 1932). Application of strychnine occurs on an average of several 

thousand acres per year out of the 21 million acres managed by the Forest Service in California, and 

diphacinone use is relatively rare, occurring in one to two campgrounds a year (Dave Bakke, USDA 

Forest Service, pers. comm.). Current laws and regulations for controlling pocket gophers with 

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Perrine, Campbell and Green 

R5-FR-010 August 2010 

strychnine are designed to minimize non-target species mortality by applying the toxin underground, 

monitoring the treatment area and removing rodent carcasses on the surface. However, even 

underground treatment for pocket gophers can cause reduction in local ground squirrel populations, and 

strychnine may remain in the gastrointestinal tracts of affected ground squirrels (Anthony and others 

1984). Therefore, a risk of secondary poisoning remains should predators or scavengers consume a 

sufficiently large number of poisoned animals. Sierra Nevada red foxes may face a higher risk than other 

predators or scavengers (e.g., birds) as pocket gophers are an important food year-round (Perrine 2005). 

Furthermore, they routinely dig gophers out of their burrows, making it likely that they would also be 

able to access poisoned carcasses and residual traces of bait belowground. The risk may be higher with 

the use of anticoagulant rodenticides such as diphacinone. As a first-generation anti-coagulant, 

diphacinone has relatively low toxicity to rodents and requires multiple applications to ensure effective 

treatment. These baits typically are applied aboveground, and evidence suggests that secondary 

poisonings are possible if a predator consumes the gastrointestinal tract or cheek pouches of poisoned 

rodents (Mendenhall and Pank 1980; Hegdal and others 1981; Littrell 1990). These treatments are usually 

applied at recreation sites such as campgrounds, which may increase the exposure to human-habituated 

red foxes. Although the risk of poisoning may be low, especially if appropriate precautions are taken and 

if standard protocols are closely followed, further investigation of the possible impacts of rodenticides 

may be warranted given the importance of pocket gophers and ground squirrels as red fox prey. 

Climate Change 

The available evidence agrees that all three western mountain red fox subspecies are closely associated 

with boreal and subalpine habitats at high elevations (Bailey 1931 and 1936; Grinnell and others 1937; 

Schempf and White 1977; Aubry 1983; Fuhrmann 1998; Swanson and others 2005; Perrine 2005). Aubry 

(1983) hypothesized that these three subspecies were adapted to the boreal conditions that were 

widespread in the contiguous United States during the last glaciation, and then became isolated in 

mountainous regions when the glaciers retreated (Aubry and others 2009). Whether due to physiological 

or behavioral limitations, or to other mechanisms which remain unclear, these montane subspecies do not 

show the wide range of habitat tolerances that is more commonly associated with the red fox (Aubry 

1984; Buskirk and Zielinski 2003). As an apparently obligate inhabitant of boreal and subalpine 

communities, the Sierra Nevada red fox may be strongly affected by climate change. Such effects include 

the direct effects of temperature, precipitation and habitat structure, as well as the cascading ecological 

interactions that may occur within these high-elevation communities. 

Over the past century, average temperatures in alpine regions have increased 0.3 to 0.6°C, 

resulting in dramatic glacial retreat (Oerlemans 1994). This warming trend is expected to continue due to 

the increasing concentration of carbon dioxide and other greenhouse gases in the atmosphere. These 

gases are expected to double well before the year 2100, with estimated increases of between 1.4 and 5.8°C 

in global mean temperature (IPCC 2001). In California, temperature increases would be highest in the 

higher elevations of the Sierra Nevada, with a projected increase in average annual temperature of 3.8°C 

(Snyder and others 2002). The temperature increase would likely be accompanied by a dramatic decrease 

in snow accumulation at high elevations. Weather station records from the western US indicate that 

these trends have already commenced, with increasing winter and spring temperatures causing 

precipitation to fall as rain rather than snow (Knowles and others 2006). In the Great Basin, a 3°C 

increase in annual temperature would raise the lower limit of the boreal zone 500 m and cause a 62% 

reduction in boreal habitat (McDonald and Brown 1992; Moen and others 2004). A similar calculation for 

the Sierra Nevada would suggest a 50% reduction in boreal habitat based on elevational gradients alone, 

30
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sierra Nevada Red Fox 

Conservation Assessment 

and an even greater reduction given the amount of rockland and icefield habitats found above 2,750 m. 

Such warming could facilitate the movement of coyotes, bobcats, and lowland red foxes into habitats 

currently occupied by mountain red fox, possibly resulting in increased competition and predation rates 

and increased risk of competitive exclusion and disease transmission. 

Currently, too little research has been conducted on the Sierra Nevada red fox to identify the 

specializations or limitations that restrict them to boreal environments. However, the extinction of a 

number of boreomontane-adapted animals during the last climatic warming (e.g., noble marten [Martes 

nobilis]; Grayson 1984 and 1987), or their elimination from mountain ranges south of their current 

distribution (e.g., mountain goats [Oreamnos americanus] in the Sierra Nevada and hoary marmot 

[Marmota caligata] in the southern Cascades; Hoffmann and Taber 1967), suggests that climate change 

may pose a very real threat to the Sierra Nevada red fox. While the Sierra Nevada red fox may have 

survived the 1.5°C higher average temperature of the last climatic warming (the altithermal of 6,000 yrs 

ago), it may not survive the much greater temperature increase projected for the next 100 years. 

Trapping 

Red fox trapping has been banned in California since 1974. Furthermore, the state passage of Proposition 

4 in 1998 prohibited the use of all body-gripping traps for commercial purposes. Therefore, trapping 

likely has a minimal impact upon Sierra Nevada red foxes. However, due to the apparent low densities 

and isolated nature of Sierra Nevada red fox populations, incidental trapping or poaching could 

represent a threat, albeit small, to local populations. 

Summary of Potential Threats 

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. 

CONSERVATION CONSIDERATIONS 

This section identifies considerations or opportunities that may assist in the conservation of the Sierra 

Nevada red fox in California. Developing management considerations for this species is challenging due 

to the paucity of knowledge about its distribution and ecology. The isolated nature of Sierra Nevada red 

fox populations suggests that incidental detections may occur rarely. However, until additional rigorous, 

focused research or systematic monitoring can be conducted, the slow accumulation of incidental 

detections or samples from researchers or managers conducting other projects may be the only practical 

way to acquire information. 

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Because of the urgent need to document the distribution of this species, the most efficient way to 

proceed may be to make minor adjustments to the field protocols for ongoing surveys for other species 

such as marten, fisher and wolverine (see details below). These modifications could be implemented in 

the historic range of the Sierra Nevada red fox and in habitat types similar to those in which red foxes 

have been documented in the Lassen region. 

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 and others 1937; Perrine 2005), the availability and 

maintenance of movement corridors from upper elevation areas to the mixed conifer zone will be 

important. 

Although the sensitivity of Sierra Nevada red fox to human presence is debatable, the negative 

impacts of direct human-wildlife interactions are not. Red foxes are intelligent and adaptable, and can 

quickly become acclimated to humans. Accounts of red foxes scavenging at houses, campgrounds and 

parking lots, and even directly approaching humans and vehicles during daytime, have been 

documented in the Lassen region (Perrine and Arnold 2001; Perrine 2005) and for other mountain fox 

populations (Aubry 1983; Tsukada 1997; Bubela and others 1998). 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. 

In the Lassen region, radio-collared red foxes were highly mobile, with large home ranges and 

extensive daily and seasonal movements, and they routinely crossed administrative boundaries during 

the course of normal foraging behavior (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. 

INVENTORY, MONITORING, AND RESEARCH NEEDS 

Woefully little information exists on the distribution and ecology of mountain red fox in California. 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 twopronged 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). 

Documenting the current distribution of Sierra Nevada red fox throughout its historical range is 

essential. The collection of anecdotal sighting reports, although important, is insufficient to reliably 

document what proportion of Sierra Nevada red fox historical range remains occupied. Methods to 

detect forest-associated carnivores have been well developed over the past decade (e.g., Zielinski and 

Kucera 1995). These methods consist primarily of sooted track plates, remote camera systems, and snow 

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Sierra Nevada Red Fox 

Conservation Assessment 

tracking. However, 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 (Halfpenny and others 1995) 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 (e.g., Smith and others 2003) 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. 

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 

(Roest 1977; Lewis and others 1995; Aubry 1997; Perrine et al 2007). 

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 (Van Horne 1983; Pulliam 1988). 

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 

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and federal entities would facilitate the compilation of genetic material. Such entities obviously include 

the land management agencies listed above, 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. 

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Perrine, Campbell and Green 

R5-FR-010 August 2010 

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PERSONAL COMMUNICATIONS 

Bakke, Dave. USDA Forest Service, Pacific Southwest Regional Office. Vallejo, CA. 

Chow, Les. US Geological Survey. Yosemite National Park, CA. 

Graber, David. National Park Service, Sequoia and Kings Canyon National Parks. Three Rivers, CA. 

Rickman, Tom. Lassen National Forest, Eagle Lake Ranger District. Susanville, CA. 

Van Vuren, Dirk. University of California. Davis, CA. 

PHOTO CREDITS 

Cover Photo: Keith Slauson, USDA Forest Service, Pacific Southwest Research Station 

Inside Front Cover: John Perrine, University of California, Berkeley 

Photo Page ii: John Perrine, University of California, Berkeley 

Photo Page 6: Keith Slauson, USDA Forest Service, Pacific Southwest Research Station 

Inside Back Cover: John Perrine, University of California, Berkeley 

42
 

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