Fox squirrel's range (excludes introduced populations)
The fox squirrel (Sciurus niger), also known as the eastern fox squirrel or Bryant's fox squirrel,[3] is the largest species of tree squirrel native to North America. It is sometimes mistaken for the American red squirrel or eastern gray squirrel in areas where the species co-exist, though they differ in size and coloration.[5]
The fox squirrel's total length measures 20 to 30in (50.8 to 76.2cm), with a body length of 10 to 15in (25.4 to 38.1cm) and a similar tail length. They range in weight from 1.0 to 2.5lb (453.6 to 1,134.0g).[6] There is no sexual dimorphism in size or appearance. Individuals tend to be smaller in the West. There are three distinct geographical morphs in coloration. In most areas, the animal's upper body is brown-grey to brown-yellow with a typically brownish-orange underside, while in eastern regions, such as the Appalachians, there are more strikingly-patterned dark brown and black squirrels with white bands on the face and tail. In the South and parts of Nebraska and Iowa along the Missouri River,[7] there are populations with uniform black coats.
To help with climbing, the squirrels have sharp claws, developed extensors of digits and flexors of forearms, and abdominal musculature.[8] Fox squirrels have excellent vision and well-developed senses of hearing and smell. They use scent-marking to communicate with other fox squirrels.[8] "Fox squirrels also have several sets of vibrissae, hairs or whiskers that are used as touch receptors to sense the environment. These are found above and below their eyes, on their chin and nose, and on each forearm."[8] The dental formula of S. niger is 1.0.1.31.0.1.3 × 2 = 20.[9]
Fox squirrels are most abundant in open forest stands with little understory vegetation; they are not found in stands with dense undergrowth. Ideal habitat is small stands of large trees interspersed with agricultural land.[14] The size and spacing of pines and oaks are among the important features of fox squirrel habitat. The actual species of pines and oaks themselves may not always be a major consideration in defining fox squirrel habitat.[6] Fox squirrels are often observed foraging on the ground several hundred meters from the nearest woodlot. Fox squirrels also commonly occupy forest edge habitat.[15]
Fox squirrels have two types of shelters: leaf nests (dreys) and tree dens. They may have two tree cavity homes or a tree cavity and a leaf nest. Tree dens are preferred over leaf nests during the winter and for raising young. When den trees are scarce, leaf nests are used year-round.[16][17] Leaf nests are built during the summer months in forks of deciduous trees about 30 feet (9 m) above the ground. Fox squirrels use natural cavities and crotches (forked branches of a tree) as tree dens.[16] Den trees in Ohio had an average diameter at breast height (d.b.h.) of 21 inches (53cm) and were an average of 58.6 yards (53.6m) from the nearest woodland border. About 88% of den trees in eastern Texas had an average d.b.h. (diameter at breast height) of 12 inches (30cm) or more.[14] Dens are usually 6 inches (15cm) wide and 14–16 inches (36–41cm) inches deep. Den openings are generally circular and about 2.9 to 3.7 inches (7.4 to 9.4cm). Fox squirrels may make their own den in a hollow tree by cutting through the interior; however, they generally use natural cavities or cavities created by northern flickers (Colaptes auratus) or red-headed woodpeckers (Melanerpes erythrocephalus). Crow nests have also been used by fox squirrels.[17]
Fox squirrels use leaf nests or tree cavities for shelter and litter rearing.[14] Forest stands dominated by mature to over-mature trees provide cavities and a sufficient number of sites for leaf nests to meet the cover requirements. Overstory trees with an average d.b.h. of 15 inches (38cm) or more generally provide adequate cover and reproductive habitat. Optimum tree canopy closure for fox squirrels is from 20% to 60%. Optimum conditions of understory closure occur when the shrub-crown closure is 30% or less.[14]
Fox squirrels are tolerant of human proximity, and even thrive in crowded urban and suburban environments. They exploit human habitations for sources of food and nesting sites, being as happy nesting in an attic as they are in a hollow tree.[18]
As an invasive species
In Europe, Sciurus niger has been included since 2016 in the list of Invasive Alien Species of Union concern (the Union list).[19] This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.[20]
Behavior and ecology
A backyard fox squirrel searching for a location to bury its acorn, in Berkeley, CaliforniaManipulation of food items by the paws and head
Fox squirrels are strictly diurnal, non-territorial, and spend more of their time on the ground than most other tree squirrels. They are still, however, agile climbers. They construct two types of homes called "dreys", depending on the season. Summer dreys are often little more than platforms of sticks high in the branches of trees, while winter dens are usually hollowed out of tree trunks by a succession of occupants over as many as 30 years. Cohabitation of these dens is not uncommon, particularly among breeding pairs.
Fox squirrels will form caches by burying food items for later consumption.[9] They like to store foods that are shelled and high in fat, such as acorns and nuts. Shelled foods are favored because they are less likely to spoil than non-shelled foods, and fatty foods are valued for their high energy density.[21][22]
Fox squirrels are not particularly gregarious or playful; in fact, they have been described as solitary and asocial creatures, coming together only in breeding season.[23] They have a large vocabulary, consisting most notably of an assortment of clucking and chucking sounds, not unlike some "game" birds, and they warn of approaching threats with distress screams. In the spring and autumn, groups of fox squirrels clucking and chucking together can make a small ruckus. They also make high-pitched whines during mating. When threatening another fox squirrel, they will stand upright with their tail over their back and flick it.[8] Fox squirrels are impressive jumpers, easily spanning 15 feet in horizontal leaps and free-falling 20 feet or more to a soft landing on a tree limb or tree trunk.
In Illinois, fox squirrels rely heavily on hickories from late August through September. Pecans, black walnuts (Juglans nigra), osage orange (Maclura pomifera) fruits, and corn are also important fall foods. In early spring, elm buds and seeds are the most important food. In May and June, mulberries (Morus spp.) are heavily used. By early summer, corn in the milk stage becomes a primary food.[24]
During the winter in Kansas, osage orange is a staple item supplemented with seeds of the Kentucky coffee tree (Gymnocladus dioicus) and honey locust (Gleditsia triacanthos), corn, wheat, eastern cottonwood (Populus deltoides var. deltoides) bark, ash seeds, and eastern red cedar (Juniperus virginiana) berries. In the spring, fox squirrels feed primarily on buds of elm, maple, and oaks but also on newly sprouting leaves and insect larvae.[24]
Fox squirrels in Ohio prefer hickory nuts, acorns, corn, and black walnuts. The squirrels are absent where two or more of these mast trees are missing. Fox squirrels also eat buckeyes, seeds and buds of maple and elm, hazelnuts (Corylus spp.), blackberries (Rubus spp.), and tree bark. In March, they feed mainly on buds and seeds of elm, maple, and willow. In Ohio, eastern fox squirrels have the following order of food preference: white oak (Quercus alba) acorns, black oak (Quercus velutina) acorns, red oak (Quercus rubra) acorns, walnuts, and corn.[24]
In eastern Texas, fox squirrels prefer the acorns of bluejack oak, pecans, southern red oak (Q. falcata), and overcup oak (Q. lyrata). The least preferred foods are acorns of swamp chestnut oak (Q. michauxii) and overcup oak. In California, fox squirrels feed on English walnuts (J. regia), oranges, avocados, strawberries, and tomatoes. In midwinter, they feed on eucalyptus seeds.[24]
In Michigan, fox squirrels feed on a variety of foods throughout the year. Spring foods are mainly tree buds and flowers, insects, bird eggs, and seeds of red maple (Acer rubrum), silver maple (Acer saccharinum), and elms. Summer foods include a variety of berries, plum and cherry pits, fruits of basswood (Tilia americana), fruits of box elder (Acer negundo), black oak acorns, hickory nuts, seeds of sugar (Acer saccharum) and black maple (Acer nigrum), grains, insects, and unripe corn. Autumn foods consist mainly of acorns, hickory nuts, beechnuts, walnuts, butternuts (Juglans cinerea), and hazelnuts. Caches of acorns and hickory nuts are heavily used in winter.[24]
Reproduction
A fox squirrel pup
Female fox squirrels come into estrus in mid-December or early January, then again in June. They normally produce two litters a year; however, yearling females may only produce one.[24] Females become sexually mature at 10 to 11 months of age and usually produce their first litter when they are 1 year old.[24]
Gestation occurs over a period of 44 to 45 days. The earliest litters appear in late January; most births occur in mid-March and July. The average litter size is three, but can vary according to season and food conditions.[24]
Tree cavities, usually those formed by woodpeckers, are remodeled into winter dens and often serve as nurseries for late winter litters. If existing trees lack cavities, leaf nests known as dreys are built by cutting twigs with leaves and weaving them into warm, waterproof shelters. Similar leafy platforms are built for summer litters and are often called "cooling beds."[25]
Fox squirrels, like other tree squirrels, develop slowly compared to others. At birth, the young are blind, without fur, and helpless. Their eyes open at 4 to 5 weeks and their ears open at 6 weeks. Fox squirrels are weaned between 12 and 14 weeks, but may not be self-supporting until 16 weeks.[17][24] Juveniles usually disperse in September or October, but may den either together or with their mother during their first winter.[16]
Mortality
In captivity, fox squirrels have been known to live about 18 years, but in the wild, most fox squirrels die before they become adults.[8] Their maximum life expectancy is typically 12.6 years for females and 8.6 years for males. Because of overhunting and the destruction of mature forests, many subspecies of fox squirrel are endangered.[8] Another major cause of fox squirrel population decline is mange mites (Cnemidoptes spp.) along with severe winter weather.[24]
Relatively few natural predators can regularly capture adult fox squirrels. Of these predators, most only take fox squirrels opportunistically.[6] Predators include bobcats (Lynx rufus), Canada lynx (Lynx canadensis), red foxes (Vulpes vulpes), gray foxes (Urocyon cinereoargenteus), red-tailed hawks (Buteo jamaicensis), red-shouldered hawks (Buteo lineatus), great horned owls (Bubo virginianus), barred owls (Strix varia), and coyotes (Canis latrans). Former predators extirpated from most of the fox squirrel's range include cougars (Puma concolor) and wolves (Canis lupus).[6][16][24] Nestlings and young fox squirrels are particularly vulnerable to climbing predators such as raccoons (Procyon lotor), opossums (Didelphis virginiana), rat snakes (Pantherophis spp.), and pine snakes (Pituophis melanoleucus). In those states where fox squirrels are not protected, they are considered a game animal.[6] Fox squirrels were an important source of meat for European settlers in the 17th and 18th centuries. They are still hunted over most of their range.[6]
Quercus muehlenbergii, the chinquapinoak, is a deciduous species of tree in the white oak group. The species was often called Quercus acuminata in older literature. Quercus muehlenbergii is native to eastern and central North America. It ranges from Vermont to Minnesota, south to the Florida panhandle, and west to New Mexico in the United States. In Canada it is only found in southern Ontario, and in Mexico it ranges from Coahuila south to Hidalgo.
Quercus velutina, the black oak, is a species of oak in the red oak group, native and widespread in eastern and central North America. It is sometimes called the eastern black oak.
The southern flying squirrel or the assapan is one of three species of flying squirrel found in North America. It is found in deciduous and mixed woods in the eastern half of North America, from southeastern Canada to Florida. Disjunct populations of this species have been recorded in the highlands of Mexico, Guatemala, and Honduras.
The northern flying squirrel is one of three species of the genus Glaucomys, the only flying squirrels found in North America. They are found in coniferous and mixed coniferous forests across much of Canada, from Alaska to Nova Scotia, and south to the mountains of North Carolina and west to Utah in the United States. They are light brown with pale underparts and grow to a length of 25 to 37 cm. They are proficient gliders but uncoordinated walkers on the ground. They feed on a variety of plant material as well as tree sap, fungi, insects, carrion, bird eggs and nestlings. They mostly breed once a year in a cavity lined with lichen or other soft material. Except when they have young, they change nests frequently, and in winter a number of individuals may huddle together in a shared nest. Unlike most members of their family, flying squirrels are strictly nocturnal.
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.
The western gray squirrel 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 ; S. g. nigripes ; and S. g. anthonyi.
The red squirrel, also called Eurasian red squirrel, is a species of tree squirrel in the genus Sciurus. It is an arboreal and primarily herbivorous rodent and common throughout Eurasia.
The acorn is the nut of the oaks and their close relatives. It usually contains a seedling surrounded by two cotyledons, enclosed in a tough shell known as the pericarp, and borne in a cup-shaped cupule. Acorns are 1–6 cm long and 0.8–4 cm on the fat side. Acorns take between 5 and 24 months to mature; see the list of Quercus species for details of oak classification, in which acorn morphology and phenology are important factors.
A drey is the nest of a tree squirrel, flying squirrel or ringtail possum. Dreys are usually built of twigs, dry leaves, and grass, and typically assembled in the forks of a tall tree. They are sometimes referred to as "drey nests" to distinguish them from squirrel "cavity nests". In temperate regions, dreys become much more visible in the autumn, when leaf-fall reveals new nests built the previous summer or in early fall.
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.
Quercus lyrata, the overcup oak, is an oak in the white oak group. The common name, overcup oak, refers to its acorns that are mostly enclosed within the acorn cup. It is native to lowland wetlands in the eastern and south-central United States, in all the coastal states from New Jersey to Texas, inland as far as Oklahoma, Missouri, and Illinois. There are historical reports of it growing in Iowa, but the species appears to have been extirpated there. It is a slow-growing tree that often takes 25 to 30 years to mature. It has an estimated lifespan of 400 years.
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.
Carya tomentosa, commonly known as mockernut hickory, mockernut, white hickory, whiteheart hickory, hognut, bullnut, is a species of tree in the walnut family Juglandaceae. The most abundant of the hickories, and common in the eastern half of the United States, it is long lived, sometimes reaching the age of 500 years. A straight-growing hickory, a high percentage of its wood is used for products where strength, hardness, and flexibility are needed. The wood makes excellent fuel wood, as well.
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.
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.
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.
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.
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.
The Ezo flying squirrel or Ezo-momonga is a subspecies of the Siberian flying squirrel. It is endemic to Hokkaidō, Japan, part of the region once known as Ezo. In the legends of the local Ainu, the Ezo flying squirrel or A-kamui is a tutelary deity of children. Together with the Ezo chipmunk and Ezo squirrel, it is one of the three sciurids found on the island, to the north of Blakiston's Line, each having its own particular ecological niche.
The Southern fox squirrel is a subspecies of the fox squirrel. They are native to the eastern United States and currently reside in North Carolina, South Carolina, and Georgia. They can also be found in parts of southern Virginia, southeastern Alabama, and the pan handle of Florida. Their life expectancy in the wild is between 6 - 7 years, but individuals have been know to live up to 20 in captivity. Southern fox squirrels are a diurnal species.
↑ Graham, Donna. "Fox Squirrel (Sciurus niger)". Northern State University. South Dakota Department of Game, Fish and Parks. Archived from the original on 2013-01-11. Retrieved 2013-12-07.
1 2 3 4 5 6 7 8 9 Van Gelden, Richard George. (1982). Mammals of the National Parks. Baltimore, MD: Johns Hopkins University Press
1 2 3 4 5 Allen, A. W. 1982. Habitat suitability index models: fox squirrel. FWS/OBS-82/10.18. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service
↑ Dueser, Raymond D.; Dooley, James L., Jr.; Taylor, Gary J. (1988). Habitat structure, forest composition and landscape dimensions as components of habitat suitability for the Delmarva fox squirrel. In: Management of amphibians, reptiles, and small mammals in North America: Proceedings of the symposium; 1988 July 19–21; Flagstaff, AZ. Gen. Tech. Rep. RM-166. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 414–421
1 2 3 4 Banfield, A. W. F. (1974). The mammals of Canada. Toronto, ON: University of Toronto Press.
1 2 3 4 MacClintock, Dorcas. (1970). Squirrels of North America. New York: Litton Educational Publishing, Inc.
1 2 3 4 5 6 7 8 9 10 11 12 13 Chapman, Joseph A.; Feldhamer, George A., eds. 1982. Wild mammals of North America. Baltimore, MD: The Johns Hopkins University Press
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