Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Sciurus niger
(fox squirrel)

Toolbox

Datasheet

Sciurus niger (fox squirrel)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Host Animal
  • Preferred Scientific Name
  • Sciurus niger
  • Preferred Common Name
  • fox squirrel
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Chordata
  •       Subphylum: Vertebrata
  •         Class: Mammalia
  • Summary of Invasiveness
  • Sciurus niger has been introduced mostly for the aesthetic novelty and pleasure that it brings (Aprile and Chicco, 1999...

Don't need the entire report?

Generate a print friendly version containing only the sections you need.

Generate report

Pictures

Top of page
PictureTitleCaptionCopyright
Sciurus niger (Fox squirrel) with acorn.  San Francisco Bay Area, California, USA.
TitleAdult
CaptionSciurus niger (Fox squirrel) with acorn. San Francisco Bay Area, California, USA.
Copyright©Ingrid Taylar - CC BY 2.0
Sciurus niger (Fox squirrel) with acorn.  San Francisco Bay Area, California, USA.
AdultSciurus niger (Fox squirrel) with acorn. San Francisco Bay Area, California, USA.©Ingrid Taylar - CC BY 2.0
Fox squirrel (Sciurus niger) with sunflower seed.  Notre Dame Campus in South Bend, Indiana, USA
TitleAdult
CaptionFox squirrel (Sciurus niger) with sunflower seed. Notre Dame Campus in South Bend, Indiana, USA
CopyrightPublic Domain
Fox squirrel (Sciurus niger) with sunflower seed.  Notre Dame Campus in South Bend, Indiana, USA
AdultFox squirrel (Sciurus niger) with sunflower seed. Notre Dame Campus in South Bend, Indiana, USAPublic Domain

Identity

Top of page

Preferred Scientific Name

  • Sciurus niger Linnaeus, 1758

Preferred Common Name

  • fox squirrel

International Common Names

  • English: Bryant's fox squirrel
  • Spanish: ardilla zorra

Local Common Names

  • USA: Eastern fox squirrel; stump-eared squirrel

Summary of Invasiveness

Top of page

Sciurus niger has been introduced mostly for the aesthetic novelty and pleasure that it brings (Aprile and Chicco, 1999), but also to increase hunting and trapping opportunities (Davis and Brown, 1988; Long, 2003). It is able to establish viable populations from a very small number of individuals (Brown and McGuire, 1975; Aprile and Chicco, 1999; Long, 2003). Success rates of introductions appear to be extraordinarily high, even from small < 20 individuals) starting populations (Wood et al., 2007). The impact of S. niger on the native western gray (S. griseus) and Douglas squirrels (Tamiasciurus douglasii) on the western US coast is attributed to competition for resources, and is a growing conservation concern (Ingles, 1947; Robinson and McTaggart-Cowan, 1954; Linders and Stinson, 2007). Abert’s squirrels (S. aberti) in the Black Forest of Colorado have experienced a population decline attributed to competition with introduced S. niger (Fitzgerald et al., 1994).

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Chordata
  •             Subphylum: Vertebrata
  •                 Class: Mammalia
  •                     Order: Rodentia
  •                         Family: Sciuridae
  •                             Subfamily: Sciurinae
  •                                 Genus: Sciurus
  •                                     Species: Sciurus niger

Notes on Taxonomy and Nomenclature

Top of page

Ten subspecies of S. niger are recognized (Wilson and Reeder, 2005):

S. n. avicennia Howell, 1919.

S. n. bachmani Lowery and Davis, 1942.

S. n. cinereus Linnaeus, 1758.

S. n. limitis Baird, 1855.

S. n. ludovicianus Custis, 1806

S. n. niger Linnaeus, 1758.

S. n. rufiventer Geoffroy, 1803.

S. n. shermani Moore, 1956.

S. n. subauratus Bachman, 1839.

S. n. vulpinus Gmelin, 1788.

Hybridization with congeners is not known (Gurnell, 1987).

Description

Top of page

S. niger is a medium-sized tree squirrel with no sexual dimorphism in size or colour. Ranges of external measurements (in mm) are: total length, 454-698; length of tail, 200-330; length of hind foot, 51-82 (Hall, 1981). Body mass ranges from 507-1361 g (Flyger and Gates, 1982).

Coat colour varies; squirrels from the western and northern portions of the natural range are grizzled with a suffusion of buff to orange. The venter can be white to cinnamon but is usually rufous (Baumgartner, 1943; Flyger and Gates, 1982). Animals in the southeastern United States are grizzled gray to agouti to black on the dorsum with white or cream nose, ears, and feet, and a black crown and nape (Kiltie, 1992; Moore, 1956; Weigl et al., 1989). Those from the central United States coast are silvery grey and may be washed with buff on the hips, feet, and head; the tail is pale grey; the underparts are white to pale grey but may be cinnamon (Flyger and Gates, 1982). Melanism is common, especially in the southern United States (Kiltie, 1989; Kiltie, 1992). Albinism is rare (Baumgartner, 1943; Moore, 1956).

Distribution

Top of page

S. niger is native to eastern and central North America; its range is declining in eastern states, although not enough to qualify for listing in a threatened category (IUCN, 2012) except for the endangered subspecies S. n. cinereus (Wilson and Reeder, 2005). It has been introduced to western parts of both the USA and Canada (Long, 2003). It is now found in numerous locations throughout Idaho, occurring in urban and agricultural areas, and has expanded its range since initial introduction in that state and neighbouring Washington (Marshall, 1941; Wright and Weber, 1979; Larrison and Johnson, 1981; Koprowski, 1994). It is also found in Asotin County and the Seattle area of Washington (Flahaut, 1941; Yocom, 1950). It is currently found in eight counties in Oregon, but is primarily restricted to urban areas and nut tree orchards (Flyger and Gates, 1982; Verts and Carraway, 1998). It is also found in many urban areas and woodlands in the Central Valley and Coastal Range of California due to numerous introductions (Jameson and Peeters, 1988); its Californian range includes approximately 10,000 contiguous square kilometres in the Los Angeles metropolitan area (King et al., 2010) and 20,000 in central California (Claytor, 2011). Although it occurs naturally in Colorado, many populations are present because of introductions in the early 1900s (Fitzgerald et al., 1994). It is also expanding its range naturally in that state, following riparian corridors, invading urbanized areas, and inhabiting areas newly cultivated with deciduous trees (Fitzgerald et al., 1994; Geluso, 2004). It is present in Hondo, Roswell, and Carlsbad, New Mexico, and western Texas, presumably because of introductions (Frey and Campbell, 1997), however the date and source of the introductions is unknown (Findley, 1987). It has also been introduced to Pelee Island on Lake Erie in Ontario, Canada (Peterson, 1966).

Distribution Table

Top of page

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

North America

CanadaPresentPresent based on regional distribution.
-British ColumbiaLocalisedIntroduced Invasive Nagorsen, 1990
-ManitobaLocalisedNativeKoprowski, 1994
-OntarioLocalisedIntroduced1890Peterson, 1966Pelee Island on Lake Erie
-SaskatchewanLocalisedNativeKoprowski, 1994
MexicoLocalisedNativeKoprowski, 1994
USAPresentPresent based on regional distribution.
-AlabamaWidespreadNativeHall, 1981
-ArizonaLocalisedIntroducedJ. L. Koprowski, University of Arizona, Tucson, Arizona, USA, personal communication, 2011.Yuma
-ArkansasWidespreadNativeHall, 1981
-CaliforniaLocalisedIntroducedearly 1900s Invasive Jameson and Peeters, 1988; King et al., 2010; Claytor, 2011Present in significant areas of the state but not throughout
-ColoradoLocalisedNativeFitzgerald et al., 1994Also introductions in early 1900s.
-DelawareWidespreadNativeHall, 1981
-FloridaWidespreadNativeHall, 1981
-GeorgiaWidespreadNativeHall, 1981
-IdahoLocalisedIntroduced Invasive Larrison and Johnson, 1981
-IllinoisWidespreadNativeHall, 1981
-IndianaWidespreadNativeHall, 1981
-IowaWidespreadNativeHall, 1981
-KansasLocalisedNativeHall, 1981
-KentuckyWidespreadNativeHall, 1981
-LouisianaWidespreadNativeHall, 1981
-MarylandWidespreadNativeHall, 1981
-MichiganWidespreadNativeHall, 1981
-MinnesotaWidespreadNativeHall, 1981
-MississippiWidespreadNativeHall, 1981
-MissouriWidespreadNativeHall, 1981
-MontanaLocalisedIntroducedHoffman et al., 1969
-NebraskaLocalisedNativeHall, 1981
-New MexicoLocalisedIntroducedbefore 1958Frey and Campbell, 1997
-New YorkLocalisedNativeHall, 1981; Long, 2003There have also been introductions
-North CarolinaWidespreadNativeHall, 1981
-North DakotaLocalisedNativeHibbard, 1956Also introductions in 1935, 1938, 1941, 1953, and 1954
-OhioWidespreadNativeHall, 1981
-OklahomaWidespreadNativeHall, 1981
-OregonLocalisedIntroduced Invasive Verts and Carraway, 1998
-PennsylvaniaLocalisedNativeHall, 1981
-South CarolinaWidespreadNativeHall, 1981
-South DakotaLocalisedNativeHall, 1981
-TennesseeWidespreadNativeHall, 1981
-TexasLocalisedNativeFrey and Campbell, 1997; Frey et al., 2013Native to eastern part of state; introduced to western part
-VirginiaWidespreadNativeHall, 1981
-WashingtonLocalisedIntroduced1915 Invasive Yocom, 1950
-West VirginiaWidespreadNativeHall, 1981
-WisconsinWidespreadNativeHall, 1981
-WyomingLocalisedNativeHall, 1981

Introductions

Top of page
Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Arizona USA   Yuma (J. L. Koprowski, University of Arizona, Tucson, Arizona, USA, personal communication, 2011)
California USA early 1900s Intentional release (pathway cause) Yes Jameson and Peeters (1988) Both southern and northern California
Colorado USA early 1900s Intentional release (pathway cause) Yes Fitzgerald et al. (1994)
Idaho USA   Intentional release (pathway cause) Yes Larrison and Johnson (1981)
Montana USA   Intentional release (pathway cause) Yes Hoffman et al. (1969)
New Mexico USA before 1958 Intentional release (pathway cause) Yes Frey and Campbell (1997)
North Dakota USA 1935-1954 Intentional release (pathway cause) Yes Hibbard (1956)
Ontario USA 1890 Intentional release (pathway cause) Yes Peterson (1966) Pelee Island on Lake Erie
Oregon USA   Intentional release (pathway cause) Yes Verts and Carraway (1998)
Texas USA   Intentional release (pathway cause) Yes Verts and Carraway (1998)
Washington USA 1915 Intentional release (pathway cause) Yes Yocom (1950)

Risk of Introduction

Top of page

S. niger is expanding its range westward in the central USA along riparian corridors, invading urbanized areas, and inhabiting areas newly cultivated with deciduous trees (Fitzgerald et al., 1994; Geluso, 2004). In addition, it is easily live-trapped, transported, and released by home owners trying to get rid of an annoying individual, and hunters attempting to increase hunting opportunities in the new location.

Habitat

Top of page

Although found in a diversity of deciduous and mixed-forest habitats, S. niger is common in forest patches <40 ha with an open understory (Nixon and Hansen, 1987). Densities are highest in habitats composed of trees that produce winter-storable food such as oaks (Quercus), hickories (Carya), walnuts (Juglans), and pines (Pinus; Nixon and Hansen, 1987; Weigl et al., 1989).

Western range extensions are associated with riverine corridors of cottonwoods (Populus deltoides; Knapp and Swenson, 1986) and fencerows of osage orange (Maclura pomifera; Packard, 1956). In Colorado, S. niger inhabits mixed conifer-deciduous forests (Littlefield, 1984).

Habitat List

Top of page
CategoryHabitatPresenceStatus
Terrestrial-managed
Managed forests, plantations and orchards Principal habitat Natural
Urban / peri-urban areas Principal habitat Natural
Terrestrial-natural/semi-natural
Natural forests Principal habitat Natural

Hosts/Species Affected

Top of page

Damage by S. niger is considered a problem only on a local scale (Gurnell, 1987). Pecans, English walnuts, avocados, oranges, and strawberries are eaten but losses are not excessive (Flyger and Gates, 1982; Wolf and Roest, 1971). The oak wilt fungus Ceratocystis fagacearum is transmitted by S. niger under experimental conditions (Himelick and Curl, 1955).

Host Plants and Other Plants Affected

Top of page
Plant nameFamilyContext
Carya (hickories)JuglandaceaeOther

Biology and Ecology

Top of page

Genetics

The diploid number of chromosomes for S. n. rufiventer is 40; the fundamental number is 76. The X chromosome is submetacentric and the Y chromosome is acrocentric; autosomes consist of 14 metacentrics and 24 submetacentrics (Nadler and Sutton, 1967).

Reproductive Biology

Although S. niger may mate at any time in the year, most breeding is in November-February with a December peak and April-July with a June peak (Brown and Yeager, 1945; Moore, 1957). Summer breeding may not occur (McCloskey and Vohs, 1971; Weigl et al., 1989). Prior to oestrus, males follow females and smell the perineal region.  Males aggregate in the home range of a female on the morning she begins her 1-day oestrus (Koprowski, 1993). A linear dominance hierarchy forms among males; females mate with several males.

Females may bear young at 8 months of age (McCloskey and Vohs, 1971), but most do not reproduce until > 1.25 years of age (Harnishfeger et al., 1978); reproductive longevity of females may be > 12.0 years (Koprowski et al., 1988).  Female reproductive levels are extremely variable between seasons and years (Harnishfeger et al., 1978; Weigl et al., 1989). Reproduction may be tightly linked with food availability (Nixon and McClain, 1969). Prevalence of lactation fell from 88 to 0% after a poor food crop (Weigl et al., 1989).

Gestation lasts 44 or 45 days (Flyger and Gates, 1982). Average litter sizes range from 1.97 to 3.35 throughout the range of the species; the mode is 2 or 3 (Harnishfeger et al., 1978; McCloskey and Vohs, 1971). Seven foetuses have been reported (Hoover, 1954).

Physiology and Phenology

S. niger is long lived, with individuals living between 5 and 15 years (Koprowski, 1994). It is capable of dispersing great distances, with squirrels known to cross waterways (Layne, 1997), and agricultural and urban areas (Jameson and Peeters, 1988). It is capable of using a wide variety of plant and animal material for food, and possesses strong jaw muscles which enables it to open most seeds and nuts, which are excellent sources of fats and proteins (Steele and Koprowski, 2001). Nests are constructed for protection against the elements, and can either be a stick and leaf nest (drey) or a cavity in a tree (Koprowski, 1994). Many species of tree squirrel have the ability to adapt to human-impacted environments (Jameson and Peeters, 1988; Geluso, 2004).

Nutrition

S. niger feeds heavily on tree seeds, flowers, and buds of ≥21 species of oak, 8 species of hickory and pecan (Carya), walnuts, beech (Fagus grandifolia), and longleaf pine (Pinus palustris) when available (Korschgen, 1981; Nixon et al., 1968; Weigl et al., 1989). Fungi are consumed primarily in summer and winter (Korschgen, 1981; Weigl et al., 1989). Insects are usually ingested in trace amounts (Baumgartner, 1939; Bugbee and Riegel, 1945; Korschgen, 1981), as well as occasional birds and bird eggs (Packard, 1956; Shaffer and Baker, 1991).

S. niger is a classic scatterhoarder that disperses food caches. Nuts are carried in the jaws, a hole is dug with the forepaws, and the nut is buried below <2 cm) the soil surface or covered with leaf litter (Cahalane, 1942). Between 33% and 99% of cached seeds are recovered (Cahalane, 1942; Stapanian and Smith, 1984).

Climate

Top of page
ClimateStatusDescriptionRemark
Am - Tropical monsoon climate Tolerated Tropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))
Aw - Tropical wet and dry savanna climate Tolerated < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
BS - Steppe climate Tolerated > 430mm and < 860mm annual precipitation
BW - Desert climate Tolerated < 430mm annual precipitation
Cf - Warm temperate climate, wet all year Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Ds - Continental climate with dry summer Preferred Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Latitude/Altitude Ranges

Top of page
Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
26-52

Air Temperature

Top of page
Parameter Lower limit Upper limit
Mean annual temperature (ºC) 8 23
Mean maximum temperature of hottest month (ºC) 23 41
Mean minimum temperature of coldest month (ºC) -22 7

Rainfall

Top of page
ParameterLower limitUpper limitDescription
Mean annual rainfall811669mm; lower/upper limits

Natural enemies

Top of page
Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Accipiter gentilis Predator not specific
Bubo virginianus Predator not specific
Buteo jamaicensis Predator not specific
Buteo lagopus Predator not specific
Buteo lineatus Predator not specific
Buteo regalis Predator not specific
Canis latrans Predator not specific
Canis lupus Predator not specific
Canis lupus familiaris Predator not specific
Crotalus horridus Predator not specific
Didelphis virginiana Predator not specific
Elaphe obsoleta Predator not specific
Felis catus Predator not specific
Lynx rufus Predator not specific
Mustela frenata Predator not specific
Pituophis melanoleucus Predator not specific
Procyon lotor Predator not specific
Vulpes cinereoargenteus Predator not specific
Vulpes vulpes Predator not specific

Means of Movement and Dispersal

Top of page

Natural Dispersal (Non-Biotic)

Tree squirrels are capable of dispersing great distances, with squirrels known to cross waterways (Layne, 1997) and agricultural and urban areas (Jameson and Peeters, 1988). The longest dispersal movement reported for S. niger is 64.4 km (Allen, 1943).

Intentional Introduction

S. niger is easily live-trapped, transported, and released by home owners trying to get rid of an annoying individual, and hunters attempting to increase hunting opportunities in the new location.

Impact Summary

Top of page
CategoryImpact
Cultural/amenity Positive and negative
Economic/livelihood Positive and negative
Environment (generally) Positive and negative

Economic Impact

Top of page

Damage by S. niger is considered a problem only on a local scale (Gurnell, 1987). Pecans, English walnuts, avocados, oranges, and strawberries are eaten but losses are not excessive (Flyger and Gates, 1982; Wolf and Roest, 1971). The oak wilt fungus Ceratocystis fagacearum is transmitted by S. niger under experimental conditions (Himelick and Curl, 1955).

Environmental Impact

Top of page

Impact on Biodiversity

The impact of S. niger on the native western gray (S. griseus) and Douglas squirrels (Tamiasciurus douglasii) on the western US coast is attributed to competition for resources, and is a growing conservation concern (Ingles, 1947; Robinson and McTaggart-Cowan, 1954; Linders and Stinson, 2007). Abert’s squirrels (S. aberti) in the Black Forest of Colorado have experienced a population decline attributed to competition with introduced S. niger (Fitzgerald et al., 1994).

Threatened Species

Top of page
Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Sciurus aberti (Abert's squirrel)No DetailsCompetition - monopolizing resourcesFitzgerald et al., 1994
Sciurus griseusNo DetailsCompetition - monopolizing resourcesIngles, 1947; Linders and Stinson, 2007
Tamiasciurus douglasiiNo DetailsCompetition - monopolizing resourcesLinders and Stinson, 2007; Robinson and McTaggart-Cowan, 1954

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Capable of securing and ingesting a wide range of food
  • Highly mobile locally
  • Benefits from human association (i.e. it is a human commensal)
  • Long lived
  • Fast growing
  • Has high reproductive potential
  • Has high genetic variability
Impact mechanisms
  • Competition - monopolizing resources
Likelihood of entry/control
  • Difficult/costly to control

Uses

Top of page

Economic Value

Economic value is primarily from hunting and travel-related revenues.

Social Benefit

Squirrels (in general, not just this species) and chipmunks rank second to songbirds in popularity among nature watchers and photographers (Shaw and Mangun, 1984).

Environmental Services

By burying forest nuts in open grasslands, S. niger is instrumental in succession of grasslands to forests (Stapanian and Smith, 1986).

Uses List

Top of page

General

  • Research model
  • Sociocultural value
  • Sport (hunting, shooting, fishing, racing)

Human food and beverage

  • Meat/fat/offal/blood/bone (whole, cut, fresh, frozen, canned, cured, processed or smoked)

Detection and Inspection

Top of page

Nest boxes attract squirrels seeking temporary refuge or building nests for long term use (Brown and McGuire, 1975), and are important for determining success of an eradication effort or monitoring range expansion as squirrels colonize new areas. Hair tubes or snares collect hairs from individual squirrels, which is helpful to determine presence or absence in areas that are in danger of being colonized by a spreading population (Gurnellet al., 2004). Transect surveys through forested areas in or near sites of introduction can determine squirrel density and distribution (Brown and McGuire, 1975; Koprowski et al., 2005; Koprowski et al., 2006).

Similarities to Other Species/Conditions

Top of page

S. niger lacks an upper 3rd premolar, unlike S. aberti and S. griseus. Where sympatric with S. aberti, it lacks hair tufts on the ears, and the dorsal pelage is not grey (Hall, 1981; McGrath, 1987). Unlike S. griseus, introduced S. niger lacks a grey dorsum (Hall, 1981; McGrath, 1987).  S. niger is much larger (2-4x) than Tamiasciurus douglasii <300g).

Prevention and Control

Top of page

Eradication

There have been no widespread efforts to eradicate S. niger from areas where it has been introduced.

Control

Poisoning, trapping, and shooting have all been attempted.  Additional methods may include manipulation of the physical environment, namely managing forests in a way that will reduce squirrel numbers, and sterilization techniques involving vaccine-induced immuno-contraceptive treatment (Dagnall et al., 1998).

References

Top of page

Allen DL, 1943. Michigan fox squirrel management. Lansing, Michigan, USA: Michigan Department of Conservation, Game Division, 404 pp. [Michigan Department of Conservation, Game Division Publication 100.]

Aprile G; Chicco D, 1999. A new exotic species of mammal in Argentina: the red-bellied squirrel (Callosciurus erythraeus). (Nueva especie exotica de mamifero en la Argentina: la ardilla la de vientre rojo (Callosciurus erythraeus).) Mastozoologia Neotropical, 6:7-14.

Baumgartner LL, 1939. Foods of the fox squirrel in Ohio. Transactions of the North American Fish and Wildlife Conference, 4:479-484.

Baumgartner LL, 1943. Pelage studies of fox squirrels (Sciurus niger rufiventer). The American Midland Naturalist, 29:588-590.

Brown LG; Yeager LE, 1945. Fox squirrels and gray squirrels in Illinois. Illinois Natural History Survey Bulletin, 23:449-536.

Brown LN; McGuire RJ, 1975. Field ecology of the exotic Mexican red-bellied squirrel in Florida. Journal of Mammalogy, 56:405-419.

Bugbee RE; Riegel A, 1945. Seasonal food choices of the fox squirrel in Western Kansas. Transactions of the Kansas Academy of Science, 48(2):199-203.

Cahalane VH, 1942. Caching and recovery of food by the western fox squirrel. The Journal of Wildlife Management, 6:338-352.

Ceballos G; Oliva G, 2005. Los mamíferos silvestres de México (The wild mammals of Mexico)., Mexico: Comisión Nacional para el Conocimiento y Uso de la Biodiversidad and Fondo de Cultura Económica.

Claytor S, 2011. Genetic variation in the introduced Eastern fox squirrel (Sciurus niger) in California. Los Angeles, California, USA: California State University.

Dagnall J; Gurnell J; Pepper H, 1998. Barkstripping damage by gray squirrels in state forests of the United Kingdom: a review. In: Ecology and evolutionary biology of tree squirrels [ed. by Steele, M. A. \Merritt, J. F. \Zegers, D. A.]. Martinsville, USA: Virginia Museum of Natural History, 249-261. [Special Publication,Virginia Museum of Natural History.]

Davis R; Brown DE, 1988. Documentation of the transplanting of Abert's squirrels. Southwestern Naturalist, 32:490-492.

Findley JS, 1987. The natural history of New Mexican mammals. Albuquerque, USA: University of New Mexico, 164 pp.

Fitzgerald JP; Meaney CA; Armstrong DM, 1994. Mammals of Colorado. Boulder, USA: University Press of Colorado, 480 pp.

Flahaut MR, 1941. Exotic squirrels in the Seattle area. The Murrelet, 22:63-64.

Flyger V; Gates JE, 1982. Fox and gray squirrels. In: Wild mammals of North America [ed. by Chapman, J. A. \Feldhamer, G. A.]. Baltimore, USA: Johns Hopkins University, 209-229.

Frey JK; Campbell ML, 1997. Introduced populations of fox squirrel (Sciurus niger) in the Trans-Pecos and Llano Estacado regions of New Mexico and Texas. Southwestern Naturalist, 42:356-358.

Frey JK; Iglesias J; Herman K, 2013. Eastern fox squirrel (Sciurus niger): new threat to pecan orchards in far west Texas. Western North American Naturalist, 73(3):382-385. https://ojs.lib.byu.edu/ojs/index.php/wnan/index

Geluso K, 2004. Westward expansion of the eastern fox squirrel (Sciurus niger) in northeastern New Mexico and southeastern Colorado. Southwestern Naturalist, 49:111-116.

Gurnell J; Lurz PWW; Shirley MDF; Cartmel S; Garson PJ; Magris L; Steele J, 2004. Monitoring red squirrels Sciurus vulgaris and grey squirrels Sciurus carolinensis in Britain. Mammal Review, 34:51-74.

Gurnell JC, 1987. The natural history of squirrels. New York, USA: Facts on File, 201 pp.

Hall ER, 1981. The mammals of North America, Second edition. New York, USA: John Wiley and Sons, 1181 pp.

Harnishfeger RL; Roseberry JL; Klimstra WD, 1978. Reproductive levels in unexploited woodlot fox squirrels. Transactions of the Illinois State Academy of Science, 71:342-355.

Hibbard AH, 1956. Range and spread of the gray and fox squirrels in North Dakota. Journal of Mammalogy, 37:525-531.

HIMELICK EB; CURL EA, 1955. Experimental transmission of the Oak wilt fungus by caged squirrels. Phytopathology, 45(11):581-584 pp.

Hoffman RS; Wright PL; Newby FE, 1969. The distribution of some mammals in Montana. I. Mammals other than bats. Journal of Mammalogy, 50:579-604.

Hoover RL, 1954. Seven fetuses in western fox squirrel (Sciurus niger rufiventer). Journal of Mammalogy, 35:447-448.

Ingles LG, 1947. Ecology and life history of the California gray squirrel. California Fish and Game, 33:139-158.

IUCN, 2012. IUCN Red List of Threatened Species. Version 2012.2. www.iucnredlist.org/

Jameson EW Jr; Peeters HJ, 1988. Mammals of California. Berkeley, USA: University of California, 429 pp.

Kiltie RA, 1989. Wildfire and the evolution of dorsal melanism in fox squirrels, Sciurus niger. Journal of Mammalogy, 70:726-739.

Kiltie RA, 1992. Camouflage comparisons among fox squirrels from the Mississippi river delta. Journal of Mammalogy, 73:906-913.

King JL; Sue MC; Muchlinski AE, 2010. Distribution of the eastern fox squirrel (Sciurus niger) in southern California. Southwestern Naturalist, 55(1):42-49. http://www.bioone.org/doi/full/10.1894/RTS-03.1

Knapp SJ; Swenson JE, 1986. New range records for the fox squirrel in the Yellowstone River Drainage, Montana. Prairie Naturalist, 18:128.

Koprowski JL, 1993. Behavioral tactics, dominance, and copulatory success among male fox squirrels. Ethology,Ecology & Evolution, 5:169-176.

Koprowski JL, 1994. Sciurus niger. Mammalian Species, 479:1-9.

Koprowski JL, 1996. Natal philopatry, communal nesting, and kinship in fox squirrels and eastern gray squirrels. Journal of Mammalogy, 77:1006-1016.

Koprowski JL; Kellison GT; Moneysmith SL, 2005. Status of red-bellied squirrels (Sciurus aureogaster) introduced to Elliott Key, Florida. Florida Field Naturalist, 33:128-129.

Koprowski JL; Ramos N; Pasch BS; Zugmeyer CA, 2006. Observations on the ecology of the endemic Mearns's squirrel (Tamiasciurus mearnsi). Southwestern Naturalist, 51(3):426-429. http://www.bioone.org/perlserv/?request=get-document&doi=10.1894%2F0038-4909%282006%2951%5B426%3AOOTEOT%5D2.0.CO%3B2

Koprowski JL; Roseberry JL; Klimstra WD, 1988. Longevity records for the fox squirrel. Journal of Mammalogy, 69:383-384.

Korschgen LJ, 1981. Foods of fox and gray squirrels in Missouri. Journal of Wildlife Management, 45(1):260-266.

Larrison EJ; Johnson DR, 1981. Mammals of Idaho. Moscow, USA: The University Press of Idaho, 200 pp.

Layne J, 1997. Nonindigenous mammals. In: Strangers in paradise: impact and management of nonindigenous species in Florida [ed. by Simberloff, D. \Schmitz, D. \Brown, T.]. Washington DC, USA: Island Press, 157-186.

Linders MJ; Stinson DW, 2007. Washington State Recovery Plan for the Western Gray Squirrel. Olympia, USA: Washington Department of Fish and Wildlife, viii + 128 pp.

Linzey AV; Timm R; Emmons L; Reid F, 2008. Sciurus niger. IUCN Red List of Threatened Species, Version 2010. www.iucnredlist.org

Littlefield VM, 1984. Habitat interrelationships of Aberts squirrels (Sciurus aberti) and fox squirrels (Sciurus niger) in Boulder County, Colorado. Oxford, Ohio, USA: Miami University, 93 pp.

Long JL, 2003. Introduced mammals of the world: their history, distribution and influence. Wallingford, UK: CABI Publishing, xxi + 589 pp.

Marshall WH, 1941. The fox squirrel in Idaho. The Journal of Mammalogy, 22:86-87.

McCloskey RJ; Vohs Jr PA, 1971. Chronology of reproduction of the fox squirrel in Iowa. Proceedings of the Iowa Academy of Science, 78:12-15.

Mcgrath G, 1987. Relationships of nearctic tree squirrels of the genus Sciurus. Lawrence, Kansas, USA: University of Kansas, 101 pp.

Moore JC, 1956. Variation in the fox squirrel in Florida. The American Midland Naturalist, 55:41-65.

Moore JC, 1957. The natural history of the fox squirrel, Sciurus niger shermani. Bulletin of the American Museum of Natural History, 113:1-71.

Nadler CF; Sutton DA, 1967. Chromosomes of some squirrels (Mammalia-Sciuridae) from the genera Sciurus and Glaucomys. Experientia, 23:249-251.

Nagorsen DW, 1990. The mammals of British Columbia. Victoria, Canada: Royal British Columbia Museum. [Royal British Columbia Museum Memoir 4.]

Nixon CM; Hansen LP, 1987. Managing forests to maintain populations of gray and fox squirrels. Illinois Department of Conservation Technical Bulletin, 5:1-35.

Nixon CM; McClain WW, 1969. Squirrel population decline following a late spring frost. Journal of Wildlife Management, 33:353-357.

NIXON CM; WORLEY DM; McCLAIN MW, 1968. Food habits of squirrels in southeast Ohio. Journal of Wildlife Management, 32:294-305.

Packard RL, 1956. The tree squirrels of Kansas: ecology and economic importance, 11. 67 pp. [Miscellaneous Publications, Museum of Natural History, University of Kansas, 11.]

Palmer GH; Koprowski JL, 2007. Tree squirrels as invasive species: conservation and management implications. In: Managing vertebrate invasive species: proceedings of an international symposium [ed. by Witmer, G. W. \Pitt, W. C. \Fagerstone, K. A.]. Fort Collins, USA: USDA/APHIS Wildlife Services, National Wildlife Research Center.

Peterson RL, 1966. The mammals of eastern Canada. Toronto, Canada: Oxford University Press, 498 pp.

Robinson DJ; McTaggart-Cowan I, 1954. An introduced population of the gray squirrel (Sciurus carolinensis Gmelin) in British Columbia. Canadian Journal of Zoology, 32:261-282.

Shaffer BS; Baker BW, 1991. Observations of predation on a juvenile blue jay, Cyanocitta cristata, by a fox squirrel, Sciurus niger. Texas Journal of Science, 43:105-106.

Shaw WW; Mangun WR, 1984. Nonconsumptive use of wildlife in the United States. An analysis of data from the 1980 National survey of fishing, hunting and wildlife associated recreation. Resource Publication, Fish and Wildlife Service, US Department of the Interior, No. 154. 20pp.

Stapanian MA; Smith CC, 1986. How fox squirrels influence the invasion of prairies by nut-bearing trees. Journal of Mammalogy, 67:326-332.

Steele MA; Koprowski JL, 2001. North American tree squirrels. Washington DC, USA: Smithsonian Institution, 201 pp.

Verts BJ; Carraway LN, 1998. Land mammals of Oregon. Berkley, USA: University of California, 668 pp.

Weigl PD; Steele MA; Sherman LJ; Ha JC; Sharpe TL, 1989. The ecology of the fox squirrel (Sciurus niger) in North Carolina: implications for survival in the southeast. Bulletin - Tall Timbers Research Station, Tallahassee, No. 24. xii + 93 pp.

Wilson DE; Reeder DM, 2005. Mammal Species of the World. A Taxonomic and Geographic Reference (3rd ed.). Baltimore, Maryland, USA: Johns Hopkins University Press, 2142 pp. http://www.bucknell.edu/msw3/.

Wolf TF; Roest AI, 1971. The fox squirrel (Sciurus niger) in Ventura County. California Fish and Game, 57:219-220.

Wood DJA; Koprowski JL; Lurz PWW, 2007. Tree squirrel introduction: a theoretical approach with population viability analysis. Journal of Mammalogy, 88:1271-1279.

Wright GM; Weber JW, 1979. Range extensions of the fox squirrel in southeastern Washington and into adjacent Idaho. The Murrelet, 60:73-75.

Yocom CF, 1950. Fox squirrels in Asotin County, Washington. The Murrelet, 31:34.

Contributors

Top of page

27/09/11 Original text by:

John L. Koprowski, School of Natural Resources, 214 Biological Sciences East, University of Arizona, Tucson, AZ  85721, USA.

S. L. Doumas, School of Natural Resources, 214 Biological Sciences East, University of Arizona, Tucson, AZ  85721, USA.

Distribution Maps

Top of page
You can pan and zoom the map
Save map