Genus Sciurus
The Genus Sciurus includes many of the most common, bushy-tailed squirrels in North America, South America, Europe and northern Asia. Most of the urban squirrels seen in many of the cities of the world are within this genus.
The following species have galleries of images below:
Kaibab squirrel (Sciurus aberti kaibabensis)
Abert’s Squirrel (Sciurus aberti aberti)
Arizona Gray Squirrel (Sciurus arizonensis)
Eastern Gray Squirrel (Sciurus carolinensis)
Western Gray Squirrel (Sciurus griseus)
Japanese Squirrel (Sciurus lis)
Apache (Mexican) Fox Squirrel (Sciurus nayaritensis)
Eastern Fox Squirrel (Sciurus niger)
European Red Squirrel (Sciurus vulgaris)
The Kaibab squirrel (Sciurus aberti kaibabensis) is a tassel-eared squirrel that lives in the Kaibab Plateau in the Southwest United States, in an area of 20 by 40 miles (32 by 64 km). The squirrel's habitat is confined entirely to the ponderosa pine forests of the North Rim of Grand Canyon National Park and the northern section of Kaibab National Forest around the town of Jacob Lake, Arizona.
This squirrel is not found anywhere else in the world. In 1965, 200,000 acres (810 km2) of Kaibab squirrel habitat within Grand Canyon National Park and Kaibab National Forest were declared the Kaibab Squirrel National Natural Landmark.
Kaibab squirrels usually have a black belly (which is sometimes gray), white tail, tufted ears and chestnut brown head. The tufts on the ears grow longer with age and may extend 1 to 2 inches (2.5 to 5.1 cm) above the ears in the winter, and may not be visible in the summer.
The Kaibab squirrel lives in ponderosa pine forests, where it builds its nest out of twigs and pine needles. Kaibab squirrels, ponderosa pines, and the fungi which grow in the vicinity of the ponderosas exist in a symbiotic relationship. The squirrel eats acorns, fruit, and fungi (especially an underground truffle), as well as the seeds, bark, and twigs of the trees where it makes its home. The Kaibab squirrel's most significant source of food is the seeds found within ponderosa pine cones. Young squirrels are born between April and August.
In the past the Kaibab squirrel was given species status (Sciurus kaibabensis) but today is considered a subspecies of the Abert's squirrel, (Sciurus aberti).
The Kaibab squirrel is an example of evolution occurring through geographic isolation, but not because of the canyon. Compared to the Kaibab squirrel, the Abert's squirrel, with its several subspecies, has a much broader distribution and is found on the South Rim of the Grand Canyon. The difference between North Rim and South Rim Abert's squirrels has given rise to the commonly held but incorrect assumption that the canyon itself acted as a barrier preventing gene flow between the two populations. However, modern Kaibab squirrels are descended from populations of Abert's squirrels that dispersed into the Grand Canyon area following the last Ice Age.
As the climate warmed, ponderosa pine stands and the Abert's squirrels living there were limited to areas of high elevation like the Kaibab Plateau. These isolated populations eventually became modern Kaibab squirrels and, as the climate cooled again and ponderosa pines once again grew at lower elevations, other Abert's squirrel subspecies returned to the Grand Canyon area, filling in their former niches on the South Rim.
Kaibab Squirrel (Sciurus aberti kaibabensis) - Jacob Lake, Arizona North Rim subspecies
Abert's squirrel or the tassel-eared squirrel (Sciurus aberti) 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.
Abert's squirrel is named after Colonel John James Abert, an American naturalist and military officer who headed the Corps of Topographical Engineers and organized the effort to map the American West in the 19th century.
The currently accepted scientific name for Abert's squirrel is Sciurus aberti Woodhouse. There are nine recognized subspecies, including the Kaibab squirrel (S. a. kaibabensis), formerly recognized as a separate species (S. kaibabensis). The nine subspecies are listed in the Distribution section.
Abert's squirrels are 46–58 cm long with a tail of 19–25 cm. The most noticeable characteristic would be their hair ear tufts, which extend up from each ear 2–3 cm. This gives this species a striking similarity to the Eurasian red squirrel, aside from its differing dark coloration. They typically have a gray coat with a white underbelly and a very noticeable rusty/reddish colored strip down their back. Abert's squirrels found in Colorado rocky mountain foothills appear black all over as shown in the adjacent image.
Abert's squirrel is confined to the Colorado Plateau and the southern Rocky Mountains of Colorado, Utah, Arizona, and New Mexico; its range extends south in the Sierra Madre Occidental to Chihuahua and Durango in Mexico. Abert's squirrel also extends a short distance into Wyoming where ponderosa pine (Pinus ponderosa) is present.[citation needed] Abert's squirrels transplanted to the Graham and Santa Catalina Mountains of Arizona have established stable populations.[citation needed] Mellott and Choate reported Abert's squirrels present in the Spanish Peaks State Wildlife Area, 43 miles (69 km) southeast of the previously known Abert's squirrel range.
The distribution of Abert's squirrel subspecies in the Southwest is coincident with the disjunct ponderosa pine forests. Subspecies distributions are as follows:
S. a. aberti (Woodhouse) – northern Arizona
S. a. barberi (Allen) – northwestern Chihuahua
S. a. chuscensis (Goldman) – New Mexico-Arizona border area
S. a. durangi (Thomas) – Durango
S. a. ferreus (True) – Rocky Mountains, central Colorado
S. a. kaibabensis – Kaibab Plateau, northern Arizona
S. a. mimus (Merriam) – New Mexico-Colorado border area
S. a. navajo (Durrant and Kelson) – southeastern Utah
S. a. phaeurus (Allen) – northwestern and southwestern Durango and southwesternmost Chihuahua
Abert's squirrels in the US make almost exclusive use of ponderosa pine for cover, nesting, and food. In Mexico where ponderosa pines are absent, the species is found in stands of the closely related Pinus arizonica. Optimum Abert's squirrel habitat is composed of all-aged ponderosa pine stands with trees in even-aged groups, densities of 168 to 250 trees per acre (496–618/ha), and 150 to 200 square feet per acre (34.4–45.3 sq m/ha) basal area. In optimum habitat average diameter of ponderosa pines is 11 to 13 inches (28 to 33 centimetres), with Gambel oaks in the 11.8- to 14-inch (30–36 cm) diameter at breast height (d.b.h.) range. Optimum habitat has some ponderosa pine over 20 inches (51 cm) d.b.h., which are the best cone producers. Larson and Schubert report that ponderosa pine 36 to 40 inches (91 to 102 centimetres) d.b.h. produced an average of 446 cones per tree per crop. Trees less than 24 inches (61 cm) d.b.h. produced fewer than 100 cones per crop.
In central Arizona, Abert's squirrel summer home ranges averaged 18 acres (7.3 hectares) and ranged from 10 to 24 acres (4.0 to 9.7 ha). Ranges were somewhat smaller in winter. Ramey reports that the mean Abert's squirrel home range for spring and summer was 20 acres (8.1 hectares) in Black Forest, Colorado. Subadult males had spring home ranges of about 27 acres (11 hectares), and adult females had somewhat larger summer home ranges than adult males. Patton reported the ranges of three squirrels as 10, 30, and 60 acres (4.0, 12.2, and 24.4 ha) in Arizona. Hall reported the home range of an adult female as 29 acres (12 hectares).
In Colorado, Ramey found a density of 83 squirrels per square mile (30/km2) in spring 1970 but only 33 squirrels per square mile (12/km2) in spring 1971. In another Colorado study, Farentinos estimated 227 squirrels per square mile (82/km2) in fall 1970 and 317 per square mile (114/km2) in fall 1971.
Abert’s Squirrel (Sciurus aberti aberti) - South Rim region of the Grand Canyon in Northern Arizona
The Arizona gray squirrel (Sciurus arizonensis) 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.
It is threatened by habitat loss. The only other large squirrel that is within its range is Abert's squirrel, which has ear tufts and lives in pine forests. Although they act and look like other gray squirrels, the Arizona gray squirrel is actually more closely related to the fox squirrel.
Sciurus arizonensis is a member of the order Rodentia and the family Sciuridae. It is distinguishable from Sciurus aberti by its longer flatter skull, broader rostrum, and having only one molar instead of two. S. arizonensis also has smaller ears with no tufts and a red/black stripe on the underside of their tail. Some sexual dimorphism can be seen in these squirrels, but it varies with some populations having larger males, and other populations having larger females.
Sciurus arizonensis or the Arizona gray squirrel can be found in parts of Arizona, New Mexico and Sonora, Mexico. They live in the mountains at mid-elevations in riparian habitats, usually broadleaf riparian habitats. The Arizona gray squirrel has had no recent expansion or reduction in the size of their range in New Mexico, though there has been some population decline. This is due to habitat loss and the introduction of Abert’s squirrel, which has in some cases outcompeted the Arizona gray squirrel for resources.
Arizona Gray Squirrel (Sciurus arizonensis) - Southeast Arizona in multiple locations
The eastern gray squirrel (Sciurus carolinensis), 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.
In Europe, Sciurus carolinensis is included since 2016 in the list of Invasive Alien Species of Union concern (the Union list). This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.
Sciurus carolinensis is native to the eastern and midwestern United States, and to the southerly portions of the central provinces of Canada. The native range of the eastern gray squirrel overlaps with that of the fox squirrel (Sciurus niger), with which it is sometimes confused, although the core of the fox squirrel's range is slightly more to the west. The eastern gray squirrel is found from New Brunswick, through southwestern Quebec and throughout southern Ontario plus in southern Manitoba, south to East Texas and Florida. Breeding eastern gray squirrels are found in Nova Scotia, but whether this population was introduced or came from natural range expansion is not known.
A prolific and adaptable species, the eastern gray squirrel has also been introduced to, and thrives in, several regions of the western United States and in 1966, this squirrel was introduced into Vancouver Island in Western Canada in the area of Metchosin, and has spread widely from there. They are considered highly invasive and a threat to both the local ecosystem and the native squirrel, the American red squirrel.
Overseas, Eastern gray squirrels in Europe are a concern because they have displaced some of the native squirrels there. They have been introduced into Ireland, Britain, Italy, South Africa, and Australia (where it was extirpated by 1973).
In Ireland, the native squirrel – also colored red – the Eurasian red squirrel S. vulgaris – has been displaced in several eastern counties, though it still remains common in the south and west of the country. The gray squirrel is also an invasive species in Britain; it has spread across the country and has largely displaced the red squirrel. That such a displacement might happen in Italy is of concern, as gray squirrels might spread to other parts of mainland Europe.
Eastern Gray Squirrel (Sciurus carolinensis) in various locations both native and introduced in California & Seattle
The western gray squirrel (Sciurus griseus) is an arboreal rodent found along the western coast of the United States and Mexico. It is a tree squirrel. 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 grey squirrel has lost habitat or experienced local extinction due to competition with other squirrel species and other pressures on their population.
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. Also, it stays in a 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.
Western Gray Squirrel (Sciurus griseus) - Southern California Mountains in San Jacinto & Los Padres National Forests
Western Gray Squirrel Melanistic Form (Sciurus griseus) in Chuchapate Campgrounds area in Los Padres National Forest - very rare form
The Japanese squirrel (Sciurus lis) is a tree squirrel in the genus Sciurus endemic to Japan. It was described by Dutch zoologist Coenraad Jacob Temminck in 1844. The Japanese squirrel's range includes the islands of Honshū, Shikoku, and Kyūshū. Recently, populations on south-western Honshū and Shikoku decreased, and those on Kyūshū disappeared. One of the factors affecting the local extinction of this species seems to be forest fragmentation by humans.
In certain areas, up to 35% of its diet can come from walnuts. It is possible the resulting dispersion has affected the evolution of larger seed sizes among Japanese walnut populations where Japanese squirrels are present. Furthermore, Japanese walnut (Juglans ailanthifolia) is an important food for Japanese squirrels in lowland mixed-species forests in Japan. Japanese squirrels feeding technique consists of opening the hard shell of walnuts by chewing along the crease of the shell, embedding its teeth into the cleft, and airing out the two parts. This strategy seems to be efficient since it minimizes the time to finish eating an entire walnut.
Japanese Squirrel (Sciurus lis) - from Nagano Prefecture, Japan
The Mexican fox squirrel (Sciurus nayaritensis) 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.
This species, or its subspecies, is sometimes called the Nayarit, Apache, or Chiricahua fox squirrel. It has been evaluated as an IUCN Red List Least Concern species.
The Mexican fox squirrel has a grizzled brown back with a yellow to rufous underside, and a charcoal tail frosted with white. Two molts occur each year; the winter pelage is more rufous and the scrotum is often ringed with white. Mass is approximately 700 grams (25 oz).
Mexican fox squirrels are diurnal, non-territorial, and do not hibernate during the winter months.
The Mexican fox squirrel forages extensively on the ground and in the forest canopy for tree seeds, flowers, and fungi. Seeds from the cones from pine, Douglas-fir, and true firs are extracted by removing individual cone scales. Acorns and walnuts are also eaten when available, along with a variety of other tree seeds, hypogeous and occasionally epigeous fungi, and insects. Mexican fox squirrels occasionally cache large seeds by scatterhoarding them in leaf litter and topsoil.
The ecology of the Mexican fox squirrel has not been studied thoroughly, particularly outside the United States. Densities are often very low. Large raptors, canids, felids, procyonids and snakes are likely the major predators.
Mexican fox squirrels typically produce a single small litter of 1 or 2 young in late spring or summer. Mexican fox squirrels nest in ball-shaped dreys composed of sticks and leaves in trees; cavities within large trees are occasionally used, especially by nursing females. They are known to communally nest at times. Mexican fox squirrels are notably silent and appear to prefer to seek cover and remain motionless. If startled, they may bark and chuck from safe locations in trees.
Mexican fox squirrels are found in forests ranging from low elevation (~1,500 metres [ 4,900 ft ]) Madrean forests with a mixture of pine and oak to higher elevation mixed conifer forests < 2,700 metres [ 8,900 ft ]. Riparian areas with large cottonwoods and sycamores often harbor the highest densities. In the United States, the squirrel lives only in the Chiricahua Mountains of southeastern Arizona.
The Mexican fox squirrel inhabits forests that were historically maintained by frequent, low-severity fire, and uses areas with open understory and large trees that are typical of such forests.
There are three subspecies.
Sciurus nayaritensis nayaritensis (Nayarit fox squirrel): southern portion of the distribution range. This is a smaller and more yellowish subspecies.
Sciurus nayaritensis apache (Apache fox squirrel): northern and central portion of the distribution range. This is a subspecies intermediate in size and coloration.
Sciurus nayaritensis chiricahuae (Chiricahua fox squirrel): an endemic subspecies of the Chiricahua Mountains of southeastern Arizona (US). Characterized as more reddish throughout.