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Home/Species/ Western Gray Squirrel

Sciurus griseus

Ord, 1818

Western Gray Squirrel

G5Secure Found in 122 roadless areas NatureServe Explorer →
G5SecureGlobal Rank
Least concernIUCN
MediumThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.104592
Element CodeAMAFB07020
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVertebrate Animal
IUCNLeast concern
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomAnimalia
PhylumCraniata
ClassMammalia
OrderRodentia
FamilySciuridae
GenusSciurus
Other Common Names
Una Ardilla (ES) western gray squirrel (EN)
Concept Reference
Wilson, D. E., and D. M. Reeder (editors). 1993. Mammal species of the world: a taxonomic and geographic reference. Second edition. Smithsonian Institution Press, Washington, DC. xviii + 1206 pp. Available online at: http://www.nmnh.si.edu/msw/.
Taxonomic Comments
Under a proposed taxonomic arrangement for Sciurini (de Abreu-Jr et al. 2020a, de Abreu-Jr et al. 2020b), Sciurus griseus (along with S. aberti ) would be moved to the genus Hesperosciurus; pending further investigation, this arrangement is tentatively not accepted following the American Society of Mammalogists (2024).
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2025-04-23
Change Date1996-11-06
Edition Date2025-04-23
Edition AuthorsGundy, R. L. (2025)
Threat ImpactMedium
Range Extent200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Number of Occurrences> 300
Rank Reasons
This species is widespread in the western United States and Baja California, México. The population has been declining slightly for decades. It is threatened by habitat loss, habitat fragmentation, competition from invasive squirrel species, and natural diseases.
Range Extent Comments
This species is found in the western United States and northwestern México. The range extends from Lake Chelan and Tacoma, Washington southward through central and western Oregon, western Nevada, the coast ranges and Sierra Nevada of California to the montane areas of southern California, and Baja California as far south as Cataviña (Carraway and Verts 1994, USFWS 2004, Escobar-Flores et al. 2011, Sultaire et al. 2024). Ranges to 2590 m in the San Bernardino Mountains, California (Carraway and Verts 1994). Using Global Biodiversity Information Facility (GBIF) (2025) records, range extent is estimated to be approximately 1,000,000 km² (RARECAT 2025).
Occurrences Comments
There are hundreds of occurrences throughout the range.
Threat Impact Comments
Habitat loss, habitat fragmentation, and loss of connection between canopy trees has attributed to local declines (Cooper and Muchlinski 2015, Stuart et al. 2018, Tran et al. 2022). Intentionally-introduced squirrels that are native to the eastern United States, particularly eastern fox squirrel (Sciurus niger) and eastern gray squirrel (Sciurus carolinensis), are causing local declines of this species, particularly in urban settings (Tran et al 2022). Notoedric mange has caused large-scale population declines in the San Bernardino Mountains, California (Stephenson et al. 2013). Large highways also greatly restrict movement of this species (Cooper and Muchlinski 2015).
Ecology & Habitat

Habitat

Fairly open oak and pine-oak forests primarily in the Upper Sonoran and Transition life zones; also in riparian woods and in lowland groves of native walnuts in California. Arboreal and terrestrial. Nests made of sticks, twigs and leaves are built in tree cavities or on the limbs of trees.

Brood dens typically are in tree cavities, often in old woodpecker holes; young may be moved to stock nest after being born in a tree-hole nest.

Ecology

Population density may vary with food supply and occurrence of epizootics; density was about 2-4/ha in several areas in California, about double this in one area in Oregon (see Carraway and Verts 1994).

May compete with other squirrels for food and nest sites.

Bobcats, coyotes, foxes, owls, and large hawks are important predators.

Reproduction

Copulation occurs primarily in winter and spring. Gestation lasts about 44 days. Adult females annually produce one litter of 2-5 (average 2-3) young, mainly from February to June or July in California. Young are born naked and blind. Sexually mature in 10-11 months.
Terrestrial Habitats
Forest - HardwoodForest - MixedWoodland - HardwoodWoodland - Mixed
Other Nations (1)
United StatesN5
ProvinceRankNative
OregonS4Yes
NevadaS4Yes
WashingtonS2Yes
CaliforniaSNRYes
Threat Assessments
ThreatScopeSeverityTiming
4 - Transportation & service corridorsLarge (31-70%)UnknownHigh (continuing)
4.1 - Roads & railroadsLarge (31-70%)UnknownHigh (continuing)
5 - Biological resource useRestricted (11-30%)Extreme - seriousHigh (continuing)
5.3 - Logging & wood harvestingRestricted (11-30%)Extreme - seriousHigh (continuing)
8 - Invasive & other problematic species, genes & diseasesRestricted (11-30%)Serious or 31-70% pop. declineHigh (continuing)
8.1 - Invasive non-native/alien species/diseasesRestricted (11-30%)Serious or 31-70% pop. declineHigh (continuing)
8.2 - Problematic native species/diseasesRestricted - smallSerious or 31-70% pop. declineHigh (continuing)

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Roadless Areas (122)
California (107)
AreaForestAcres
AgnewSequoia National Forest9,561
AntimonyLos Padres National Forest40,911
Arroyo SecoAngeles National Forest4,703
Barker ValleyCleveland National Forest11,940
Bell QuinbyShasta-Trinity National Forest11,556
Black ButteLos Padres National Forest5,116
Black Mtn.Sequoia National Forest15,102
Bonanza KingShasta-Trinity National Forest16,402
Burnt Lava FlowModoc National Forest8,387
Cahuilla MountainSan Bernardino National Forest6,952
CalienteCleveland National Forest5,953
CamuesaLos Padres National Forest8,209
ChannellSequoia National Forest45,429
ChicoSequoia National Forest39,836
Circle MountainSan Bernardino National Forest6,375
City CreekSan Bernardino National Forest9,997
ColdwaterCleveland National Forest8,402
Cow CreekShasta-Trinity National Forest22,627
Cow CreekSix Rivers National Forest1,271
Coyote NorthInyo National Forest11,932
Crane Mtn.Modoc National Forest1,269
Crystal CreekSan Bernardino National Forest6,783
Cucamonga AAngeles National Forest1,249
Cucamonga BSan Bernardino National Forest11,933
Cucamonga CSan Bernardino National Forest4,106
Cutca ValleyCleveland National Forest14,530
Deep CreekSan Bernardino National Forest23,869
Devil GulchSierra National Forest30,490
DomeStanislaus National Forest11,085
Dry LakesLos Padres National Forest17,043
EagleStanislaus National Forest16,116
EagleShasta-Trinity National Forest6,553
Ferguson RidgeSierra National Forest6,104
Fox MountainLos Padres National Forest52,072
Granite ChiefTahoe National Forest6,546
Granite PeakSan Bernardino National Forest450
Greenhorn CreekSequoia National Forest28,226
GrindstoneMendocino National Forest26,031
Grouse LakesTahoe National Forest19,085
Hixon FlatSan Bernardino National Forest8,095
Horse Creek RidgeSan Bernardino National Forest8,969
Iceberg - Mill CreekHumboldt-Toiyabe National Forest26,988
IshiLassen National Forest21,805
KellySix Rivers National Forest5,195
Kings RiverSierra National Forest52,999
Little French CShasta-Trinity National Forest11,529
Malduce BuckhornLos Padres National Forest14,177
MatilijaLos Padres National Forest5,218
Middle YubaTahoe National Forest7,379
Mill CreekSequoia National Forest27,643
Mill PeakSan Bernardino National Forest7,884
MonarchSierra National Forest697
MonoLos Padres National Forest28,141
MosesSequoia National Forest22,077
Mt. Shasta AShasta-Trinity National Forest676
Mt. Shasta BShasta-Trinity National Forest2,809
Mt. VidaModoc National Forest7,771
NordhoffLos Padres National Forest12,031
North Fork American RiverTahoe National Forest38,495
North Fork Middle Fork American RiverTahoe National Forest11,245
North Fork SmithSix Rivers National Forest37,898
North LakeInyo National Forest2,406
North MountainStanislaus National Forest7,856
Orleans Mtn.Klamath National Forest49,090
Orleans Mtn. BSix Rivers National Forest17,183
Orleans Mtn. CSix Rivers National Forest15,589
PaiuteInyo National Forest58,712
Pleasant ViewAngeles National Forest26,395
PyramidEldorado National Forest24,347
Pyramid Peak BSan Bernardino National Forest7,194
Raymond PeakStanislaus National Forest3,646
Raywood Flat BSan Bernardino National Forest11,373
RinconSequoia National Forest54,610
Rock Creek WestInyo National Forest3,626
Rouse HillSan Bernardino National Forest13,745
RussianKlamath National Forest21,771
San DimasAngeles National Forest7,160
San Gabriel AddAngeles National Forest2,527
San SevaineSan Bernardino National Forest6,866
Santa CruzLos Padres National Forest21,182
Sawmill - BadlandsLos Padres National Forest51,362
ScodiesSequoia National Forest725
Sespe - FrazierLos Padres National Forest106,910
Sheep MountainAngeles National Forest21,098
Sill HillCleveland National Forest5,294
SiskiyouKlamath National Forest54,039
Slate Mtn.Sequoia National Forest12,299
Slide CreekSix Rivers National Forest11,458
SnoozerKlamath National Forest23,414
SoliderSix Rivers National Forest14,918
South ForkShasta-Trinity National Forest16,786
South SierraSequoia National Forest8,008
Strawberry PeakAngeles National Forest7,245
SugarloafSan Bernardino National Forest8,206
Table Mtn.Inyo National Forest4,215
TequepisLos Padres National Forest9,080
Timbered CraterLassen National Forest4,096
TinemahaInyo National Forest27,060
Trail LakeLassen National Forest1,124
West ForkAngeles National Forest1,169
West GirardShasta-Trinity National Forest37,516
WestforkAngeles National Forest4,407
White LedgeLos Padres National Forest18,632
Wild Horse Mtn. (CA)Humboldt-Toiyabe National Forest28,822
Wonoga Pk.Inyo National Forest11,272
WoodpeckerSequoia National Forest11,936
WoolstaffSequoia National Forest41,445
Nevada (4)
AreaForestAcres
Jobs Peak (NV)Humboldt-Toiyabe National Forest1,342
Rose - Alum CreekHumboldt-Toiyabe National Forest853
Rose - GalenaHumboldt-Toiyabe National Forest3,711
Rose - Whites CanyonHumboldt-Toiyabe National Forest2,568
Oregon (8)
AreaForestAcres
Crane MountainFremont National Forest23,096
Hardesty MountainWillamette National Forest3,754
Hardesty MountainUmpqua National Forest2,597
LastUmpqua National Forest7,666
Metolius BreaksDeschutes National Forest11,141
Mt. JeffersonDeschutes National Forest2,282
North KalmiopsisSiskiyou National Forests91,560
North PaulinaDeschutes National Forest19,670
South Dakota (1)
AreaForestAcres
Indian CreekBuffalo Gap National Grassland24,666
Texas (1)
AreaForestAcres
Big CreekNational Forests in Texas1,447
Washington (1)
AreaForestAcres
ChelanWenatchee National Forest74,650
References (32)
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