Western gray squirrel

Last updated

Contents

Western gray squirrel
WesternGraySquirrel1.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Sciuridae
Genus: Sciurus
Species:
S. griseus
Binomial name
Sciurus griseus
Ord, 1818
Subspecies [2]
  • S. g. griseus
  • S. g. anthonyi
  • S. g. nigripes
Western gray squirrel habitat map.png
Western gray squirrel's range

The western gray squirrel (Sciurus griseus) is a tree squirrel found along the western coast of the United States and Mexico. In some places, this species has also been known as the silver-gray squirrel, the California gray squirrel, the Oregon gray squirrel, the Columbian gray squirrel and the banner-tail. There are three geographical subspecies: Sciurus griseus griseus (central Washington to the western Sierra Nevada in central California); S. g. nigripes (from south of San Francisco Bay to San Luis Obispo County, California); and S. g. anthonyi (which ranges from San Luis Obispo to northern Baja California).

In some landscapes, the western gray squirrel has lost habitat or experienced local extinction due to competition with other squirrel species and other pressures on their population.

Description

The western gray squirrel was first described by George Ord in 1818 based on notes taken by Lewis and Clark at The Dalles in Wasco County, Oregon.

Sciurus griseus is the largest tree squirrel in the Sierra Nevada and Central California range. It has plantigrade, pentadactyl feet with two phalanges. [3] Compared with the eastern gray squirrel S. carolinensis or the fox squirrel S. niger (which have been introduced into its native range), these squirrels are shy, and will generally run up a tree and give a hoarse chirping call when disturbed. Weights vary from about .35 to 1 kilogram (0.77 to 2.20 lb), and length (including tail) from 43 to 61 centimetres (17 to 24 in). It is the largest native tree squirrel in the western coastal United States. Western gray squirrels exhibit a form of coloration known as counter shading. The dorsal fur is a silver gunmetal gray, with pure white on the underside; there may be black flecks in the tail. Ears are large but without tufts. The ears turn reddish-brown at the back in the winter. The tail is long and typically very bushy. It usually stays curved upwards in an "S" shape.

Tree squirrels undergo a complete head-to-tail molt in the spring and a rump-to-head molt in the fall. Tail hair is replaced only in the spring. Nesting mothers will use their tail hair to line birthing nests. Western gray squirrels eat berries, nuts, a variety of seeds, and the eggs of small birds. The dental formula for Sciurus griseus is 1.0.2.31.0.1.3 × 2 = 22. [4]

Reproduction

Western gray squirrels reach sexual maturity at 10 to 11 months, and at approximately one year of age, will begin breeding. [5] They mate over an extended period ranging from December through June. Young are born after approximate 44-day gestation period. Juveniles emerge from nests between March and mid-August. Litter sizes range from one to five kits which remain in the nest for a longer period than other squirrels. The kits are relatively slow in development, and will not leave the nest for six months or more, another species disadvantage when in competition with other, more-rapidly fledging squirrels. Young gray squirrels have furled tails which will not reach fullness until adulthood. This is a good indicator of age and maturity. Mother squirrels often seem to be overworked with a stressed appearance, complete with bruised and battered nipples. Mating squirrels can be very physical and will bite and injure each other. Females can be quite territorial, and will chase others away and have fairly violent altercations between themselves.

Behavior and diet

Western gray squirrels are forest dwellers, and can be found at elevations up to 2,000 m. Time on the ground is spent foraging, but they prefer to travel distances from tree to tree. They are strictly diurnal, and feed mainly on seeds and nuts, particularly pine seeds and acorns, though they will also take berries, fungus and insects. Pine nuts and acorns are considered critical foods because they are very high in oil and moderately high in carbohydrates, which help increase the development of body fat. They feed mostly in trees and on the ground. They generally forage in the morning and late afternoon for acorns, pine nuts, new tree buds, and fruits. They feed on pinecones and many other nuts in preparation for the winter.

When on alert, they will spread their tails lavishly, creating an umbrella effect that shields them and possibly provides cover from overhead predators. They are scatter-hoarders making numerous caches of food when it is abundant, and thus contribute to the seed dispersion of their food trees. Although squirrels show relatively good scent relocation abilities, some food caches are never reclaimed, becoming seedlings in the spring. Though they do not hibernate, they do become less active during the winter. Like many prey animals, they depend on auditory alerts from other squirrels or birds to determine safety. Once an alarm call is transmitted, those present will join in, and the trees become a cacophony of chirping squirrels. Western gray squirrels are prey for hawks, eagles, bobcats, cougars, coyotes, raccoons, cats, dogs and humans.

Habitat and shelter

A western gray squirrel eating a pine seeds from a pine cone SQUIRREL, WESTERN GRAY (scurius griseus) (8-21-09) santa margarita lake, slo co, ca -01 (3843297381).jpg
A western gray squirrel eating a pine seeds from a pine cone

Squirrel nests are called dreys and can be seen in trees, built from sticks and leaves wrapped with long strands of grass. There are two stick nest types made by the western gray squirrel: the first is a large, round, covered shelter nest for winter use, birthing, and rearing young. The second is more properly termed a "sleeping platform," a base for seasonal or temporary use. Both types are built with sticks and twigs and are lined with leaves, moss, lichens and shredded bark. The birthing nest may be lined with tail hair. The nest may measure 43 to 91 cm (17 to 36 in) by up to 46 cm (18 in) and is usually found in the top third of the tree. Young or traveling squirrels will also "sleep rough" when weather permits, balanced spread-eagled on a tree limb high above the forest floor. This attitude is also adopted for cooling in hot weather, a behavior also observed in raccoons.

The western gray squirrel is an arboreal species, requiring enough tree cover for arboreal travel. It resides in woody areas to build their complex nests. It lives in high and low elevations in California and finds habitats in both walnut trees and black oak trees.

The western gray squirrel has many predators, including red-tailed hawks (Buteo jamaicensis), great horned owls (Bubo virginianus), eagles (Accipitridae), bobcats (Lynx rufus), coyotes (Canis latrans), cougars (Puma concolor), domestic cats (Felis catus) and domestic dogs (Canis familiaris). However, the predation does not control the squirrel's population density. [6]

Habitat loss and competition

In Washington State, the western gray squirrel was listed as a threatened species in 1993, and was reclassified as endangered in November 2023. [7] Populations of the western gray squirrel have not recovered from past reductions. They are threatened with habitat loss, road-kill mortality and disease. Habitat has been lost due to urbanization, catastrophic wild fires, and areas of forest degraded by fire suppression and overgrazing, allowing the invasion of scotch broom. Notoedric mange, a disease caused by mites, becomes epidemic in western gray squirrel populations and is a major source of mortality. Other species, such as eastern gray squirrels, fox squirrels, California ground squirrels and wild turkeys are expanding and competing with the western gray squirrel. [8]

Listed as extirpated in some California areas, the western gray squirrel in southern California is generally found only in the mountains and surrounding foothill communities. Local rehabilitation experts recount that fox squirrels were released in urban regions of Los Angeles throughout the 20th century. Fox squirrels (Sciurus niger) were introduced to the Los Angeles area in about 1904. Civil War and Spanish–American War veterans residing at the Sawtelle Veterans Home on Sepulveda and Wilshire Boulevards brought fox squirrels as pets to this site from their homes in the areas surrounding the Mississippi Valley (possibly Tennessee). Other introductions of fox squirrels to the Los Angeles area may have taken place during more recent times, but detailed records are not available. These aggressive cousins drove the more reclusive western gray squirrels back into the mountains, where competition was not so strong. This non-native species introduction appears to be the largest threat in the southern California area.

See also

Related Research Articles

<span class="mw-page-title-main">Squirrel</span> Family of rodents

Squirrels are members of the family Sciuridae, a family that includes small or medium-sized rodents. The squirrel family includes tree squirrels, ground squirrels, and flying squirrels. Squirrels are indigenous to the Americas, Eurasia, and Africa, and were introduced by humans to Australia. The earliest known fossilized squirrels date from the Eocene epoch, and among other living rodent families, the squirrels are most closely related to the mountain beaver and to the dormice.

<span class="mw-page-title-main">Flying squirrel</span> Tribe of mammals

Flying squirrels are a tribe of 50 species of squirrels in the family Sciuridae. Despite their name, they are not in fact capable of full flight in the same way as birds or bats, but they are able to glide from one tree to another with the aid of a patagium, a furred skin membrane that stretches from wrist to ankle. Their long tails also provide stability as they glide. Anatomically they are very similar to other squirrels with a number of adaptations to suit their lifestyle; their limb bones are longer and their hand bones, foot bones, and distal vertebrae are shorter. Flying squirrels are able to steer and exert control over their glide path with their limbs and tail.

<span class="mw-page-title-main">Eastern gray squirrel</span> Tree squirrel native to eastern and central North America

The eastern gray squirrel, also known, particularly outside of North America, as simply the grey squirrel, is a tree squirrel in the genus Sciurus. It is native to eastern North America, where it is the most prodigious and ecologically essential natural forest regenerator. Widely introduced to certain places around the world, the eastern gray squirrel in Europe, in particular, is regarded as an invasive species.

<span class="mw-page-title-main">Red squirrel</span> Species of tree squirrel common in Europe and Asia

The red squirrel or Eurasian red squirrel is a species of tree squirrel in the genus Sciurus common throughout Europe and Asia. The red squirrel is an arboreal, primarily herbivorous rodent.

<span class="mw-page-title-main">Fox squirrel</span> Species of mammal

The fox squirrel, also known as the eastern fox squirrel or Bryant's fox squirrel, is the largest species of tree squirrel native to North America. Despite the differences in size and coloration, it is sometimes mistaken for American red squirrels or eastern gray squirrels in areas where the species co-exist.

<span class="mw-page-title-main">Tree squirrel</span> Small tree-dwelling mammals that are members of the squirrel family (Sciuridae)

Tree squirrels are the members of the squirrel family (Sciuridae) commonly just referred to as "squirrels". They include more than 100 arboreal species native to all continents except Antarctica and Oceania.

<i>Sciurus</i> Genus of rodents

The genus Sciurus contains most of the common, bushy-tailed squirrels in North America, Europe, temperate Asia, Central America and South America.

<span class="mw-page-title-main">Abert's squirrel</span> Species of rodent

Abert's squirrel or the tassel-eared squirrel is a tree squirrel in the genus Sciurus native to the southern Rocky Mountains from the United States to the northern Sierra Madre Occidental of Mexico, with concentrations found in Arizona, New Mexico, and southwestern Colorado. It is closely associated with, and largely confined to, mature ponderosa pine forests. It is named in honor of the American naturalist John James Abert; nine subspecies are recognised. It is recognizable by its tufted ears, gray color, pale underparts and rufous patch on the lower back. The squirrel feeds on the seeds and cones of the Mexican pinyon and the ponderosa pine when they are available, but will also take fungi, buds, bark, and carrion. Breeding normally occurs in summer, with a spherical nest being built high in the canopy.

<span class="mw-page-title-main">Bolivian squirrel</span> Species of rodent

The Bolivian squirrel is a tree squirrel that is endemic to South America. Little is known of the species, which may represent a species complex.

<span class="mw-page-title-main">Delmarva fox squirrel</span> Subspecies of rodent

The Delmarva fox squirrel is a formerly endangered subspecies of the fox squirrel. It is native to the eastern United States. The Delmarva fox squirrel was removed from the Endangered Species List effective December 2015.

<span class="mw-page-title-main">Caucasian squirrel</span> Species of rodent

The Caucasian squirrel or Persian squirrel, is a tree squirrel in the genus Sciurus found in temperate broadleaf and mixed forests in south-western Asia.

<span class="mw-page-title-main">Arizona gray squirrel</span> Species of rodent

The Arizona gray squirrel is a tree squirrel, in the genus Sciurus, endemic to the canyons and valleys surrounded by deciduous and mixed forests in eastern Arizona and northern Mexico.

<span class="mw-page-title-main">Collie's squirrel</span> Species of rodent

Collie's squirrel is a tree squirrel in the genus Sciurus endemic to Mexico.

<span class="mw-page-title-main">Deppe's squirrel</span> Species of rodent

Deppe's squirrel is a species of tree squirrel in the genus Sciurus native to Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, and Nicaragua.

<span class="mw-page-title-main">Mexican fox squirrel</span> Species of rodent

The Mexican fox squirrel is a species of tree squirrel found throughout the Sierra Madre Occidental of Mexico as far south as Jalisco — and northward into the Chiricahua Mountains of southeastern Arizona, U.S.

The ring-tailed ground squirrel is a species of rodent in the family Sciuridae. It is endemic to the Pacific coast region of central Mexico. It is a common species and feeds mainly on fruits and nuts. The IUCN has assessed it as being of "least concern".

<span class="mw-page-title-main">Rock squirrel</span> Species of rodent

The rock squirrel is a species of rodent in the family Sciuridae. It is native to Mexico and the Southwestern United States, including southern Nevada, Utah, Colorado, Arizona, New Mexico, West Texas, and the panhandle of Oklahoma.

<i>Sciurus ingrami</i> Species of rodent

Sciurus ingrami, usually called Ingram's squirrel in English, is a squirrel found in South America. It is known as serelepe in southeastern Brazil. It is found in the Atlantic Forest Biome of Brazil and Misiones Province, Argentina.

<span class="mw-page-title-main">Sherman's fox squirrel</span> Subspecies of rodent

Sherman's fox squirrel is a subspecies of the fox squirrel. It lives in the U.S. states of Florida and Georgia in fire-prone areas of longleaf pine and wiregrass, especially around sandhills. A tree squirrel, Sherman's fox squirrel has lost much of its habitat to farming and development. This type of squirrel nests in oak trees using leaves and Spanish moss.

References

  1. ↑ Lacher, T.; Timm, R.; Álvarez-Castañeda, S.T. (2017) [errata version of 2016 assessment]. "Sciurus griseus". IUCN Red List of Threatened Species . 2016: e.T20011A115154716. doi: 10.2305/IUCN.UK.2016-3.RLTS.T20011A22247710.en . Retrieved 10 March 2022.
  2. ↑ Thorington, R.W. Jr.; Hoffmann, R.S. (2005). "Family Sciuridae". In Wilson, D.E.; Reeder, D.M (eds.). Mammal Species of the World: a taxonomic and geographic reference (3rd ed.). The Johns Hopkins University Press. pp. 754–818. ISBN   978-0-8018-8221-0. OCLC   26158608.
  3. ↑ Carraway, Leslie N.; Verts, B. J. (1994-12-02). "Sciurus griseus". Mammalian Species (474): 1–7. doi:10.2307/3504097. ISSN   0076-3519. JSTOR   3504097. S2CID   253911325.
  4. ↑ Bryant, Monroe D. (1945). "Phylogeny of Nearctic Sciuridae". The American Midland Naturalist. 33 (2): 257–390. doi:10.2307/2421337. JSTOR   2421337.
  5. ↑ "Western Gray Squirrel". www.swartzentrover.com.
  6. ↑ Carraway, Leslie N.; Verts, B. J. (1994-12-02). "Sciurus griseus". Mammalian Species (474): 1–7. doi:10.2307/3504097. ISSN   0076-3519. JSTOR   3504097. S2CID   253911325.
  7. ↑ Li Cohen (2023-11-20). "Western gray squirrels are now considered endangered in Washington state: "Seriously threatened with extinction"". CBS News. CBS News. Retrieved 2023-12-25.
  8. ↑ "Western Gray Squirrels". WDFW Conservation. Washington Department of Fish and Wildlife. 2017-06-12. Retrieved 2018-09-27.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.