The fox squirrel (Sciurus niger), 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.
Description
The fox squirrel's total length measures , with a body length of and a similar tail length. They range in weight from . 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, there are isolated communities with uniform black coats. To help with climbing, the squirrels have sharp claws, developed extensors of digits and flexors of forearms, and abdominal musculature. Fox squirrels have excellent vision and well-developed senses of hearing and smell. They use scent-marking to communicate with other fox squirrels. "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." The dental formula of S. niger is .
Distribution
The fox squirrel's natural range extends through most of the eastern United States, north into the southern prairie provinces of Canada, and west to the Dakotas, Colorado, and Texas. They are absent (except for vagrants) in New England, New Jersey, most of New York, northern and eastern Pennsylvania, Ontario, Quebec, and the Atlantic provinces of Canada. They have been introduced to both northern and southern California, Oregon, Idaho, Montana, Washington, and New Mexico, as well as Ontario and British Columbia in Canada. While very versatile in their habitat choices, fox squirrels are most often found in forest patches of 40 hectares or less with an open understory, or in urban neighborhoods with trees. They thrive best among oak, hickory, walnut, pecan and pine trees, storing their nuts for winter. Western range extensions in Great Plains regions such as Kansas are associated with riverine corridors of cottonwood. A subspecies native to several eastern U.S. states is the Delmarva Peninsula fox squirrel (S. n. cinereus).
Invasiveness
In Europe, Sciurus niger has been 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.
Habitat
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. 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. Fox squirrels are often observed foraging on the ground several hundred meters from the nearest woodlot. Fox squirrels also commonly occupy forest edge habitat.
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. 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. Den trees in Ohio had an average diameter at breast height (d.b.h.) of and were an average of from the nearest woodland border. About 88% of den trees in eastern Texas had an average d.b.h. (diameter at breast height) of or more. Dens are usually wide and inches deep. Den openings are generally circular and about . 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.