Fox Squirrels

Distribution

Fox squirrels are found throughout the eastern United States; their natural range extends from Florida, north to Canada, and west to the Dakotas, Colorado, and Texas, but they are not found in New England.

Fox squirrels were introduced to Southern California especially Los Angeles by Fish & Game sometime in the 1930's I believe. They dropped them off at different parks and campuses including I think Larchmont Park.

General Characteristics

Fox squirrels (Sciurus niger) are the largest arboreal, or tree squirrels. There are three different color phases; in the northeastern part of their range they have grey backs with yellowish bellies, in the western part of their range they are reddish in color, and in the south they are often black with a white blaze on their face and a white tipped tail. In addition several members of the species in South Carolina have white ears. Generally, there is no difference between males and females with respect to size or coloration. They are distinguishable from their close cousin, the grey squirrel (S. carolinensis), in that grey squirrels are at least 20% smaller and have silver tipped fur.

In natural conditions, fox squirrels live to 7 or 8 years of age, although one individual lived to 18 years of age in captivity. They tend to be larger in the northern part of their range than in the southern part of their range. Their bodies measure 450 - 700 mm total length, 200 - 330 mm tail length, 51 - 82 mm right hind foot length, and they range in weight from 500 - 1000 grams. Fox squirrels have both a summer and winter coat, and therefore molt twice each year. The spring molt begins in March, whereas the autumn molt begins in September, but the tail only molts once each year during the summer.

Fox squirrels have four sets of whiskers located above and below the eyes, on the underside of the head in front of the throat, and on the nose. Whiskers, also known as vibrissae are touch receptors that provide the animal with information about its immediate surroundings. Fox squirrels have very good eyesight even in dim light, and a wide field of vision. They also have a well developed sense of smell and hearing.

Squirrels have upper and lower incisor teeth followed by a gap called a diastema. The diastema is where the canine teeth would normally be found in carnivorous animals such as cats or dogs, or omnivorous animals such as monkeys. Behind the diastema are the cheek or grinding teeth which consist of premolars and molars. As with other rodent species, the incisors continuously grow to compensate for the enormous amount of wear that comes from a herbivorous diet. Young squirrels have milk teeth which are replaced by permanent teeth when they are between six and twelve months old.

Fox squirrels are highly adapted for climbing trees and fatal falls are rare. Adaptations for climbing trees include tough curved claws for climbing and they can leap considerable distances using powerful hindlimbs. Tails are used for balance when running and leaping between trees, and held over the back of a resting animal.

Reproduction

Fox squirrels have two breeding seasons per year, and most breeding occurs in December - February and May - June of each year. Females can have two litters per year, one from each breeding season. Average litter sizes range from 2 - 4 individuals; the winter litter is generally smaller than the summer litter. Female fox squirrels are sexually mature as early as 6 months of age, but generally don't reproduce until 1 year of age. Male fox squirrels are sexually mature at 10 - 11 months of age. Functional testes descend in the scrotum from December to February and May to July, although testes may stay descended without spermatogenesis until October. Both sexes remain reproductively active throughout their lives.

Juvenile squirrels are born without hair and their eyes remain closed for about one month. Young begin to venture outside of their nest at 7 - 8 weeks of age, but generally don't travel on the ground until closer to 3 months of age.

Juvenile males are more likely to leave the natal area and disperse than are juvenile females. Dispersal usually occurs during the fall and young males move between 1 and 16 kilometers away from their natal nest. The longest recorded dispersal is 100 km. Dispersal is a high cause of mortality among males, which results in a slightly female biased sex ratio.

Habits and Ecology

Fox squirrels are active year round during the daytime. Even during the most severe winter weather they will leave their nests for short periods of time to forage for food. Activity is bimodal from late spring to autumn with peaks 2 hours after sunrise and again 2 - 5 hours before sunset.

Fox squirrels have large overlapping home ranges and are non-territorial. Fox squirrels are most commonly found in oak-hickory forests. In the south they will also be found in live oak and mixed forests, cypress and mangrove swamps, and in piney areas.

Fox squirrels are generalist feeders and their diet is dependent upon the area in which they are found. Squirrels feed heavily on nuts, flowers, and buds of 24 oak species, and 10 species of walnut, hickory and pecan. Other food items include the fruits, seeds, buds or flowers of maples, mulberry, hackberry, elms, buckeyes, horse chestnuts, wild cherries, dogwoods, hawthorne, hazelnut and ginkgo. Pine tree seeds and pollen cones are readily eaten including cedar, hemlock, pines, and spruce. Fungi are also consumed when readily available in summer, as are cultivated crops in winter. Animal food items include bones, bird eggs, nestlings, and frogs.

Food consumption peaks in summer or autumn and decreases in winter. Autumn rates of food consumption exceed energetic needs by 32% so that the animals can increase their weight before the onset of winter. Fox squirrels are classic scatterhoarders. They carry nuts in their jaws and bury them in various locations within their home ranges. Olfaction and memory are used in locating their caches.

Nests -

Fox squirrels typically use 3 different types of nests: winter dreys, summer dreys, and dens. Dreys are round conspicuous twig and leaf nests built in trees between 25 and 45 cm in diameter. They are waterproof, and made of an outer layer of interwoven twigs with a softer inner lining consisting of moss, bark, leaves, fur, feathers, lichen or other similar material. Summer dreys are less elaborate than winter dreys and may be no more than twig and leaf saucer shaped platforms on exposed branches. Dreys are generally built in the upper 1/3 of the canopy and seldom in isolated trees, which may serve to protect nests from predators.

Tree dens are another type of nest used by fox squirrels. These are holes or cavities in the main trunks of trees which are also lined with soft material. Formation of den cavities requires 8 - 30 years, and are more common in deciduous trees than in coniferous trees. Squirrels often use dens in winter months and dreys in summer months.

Skeleton and skull of a squirrel - 
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squirrelskull.jpg (23023 bytes)  squirrel_skeleton.jpg (218189 bytes)

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This page was developed and is maintained by Peg Halloran, Ph.D.
email: halloran@colorado.edu
Copyright 1997, 1998, 1999; all rights reserved of course.
Last Update: March 16, 1999 by Peg Halloran, Ph.D.