Tree Squirrels

Wildlife Damage Management July 30, 2010|Print

Tree Squirrels | Tree Squirrel Overview | Tree Squirrel Damage Assessment | Tree Squirrel Damage Management | Tree Squirrel Resources | Tree Squirrel Acknowledgments | ICWDM | Wildlife Species Information


Image:Fig1treesquirrel.jpg

Figure 1. Fox squirrel, Sciurus niger

Contents

Identification

In this chapter tree squirrels are divided into three groups: large tree squirrels, pine squirrels, and flying squirrels. Large tree squirrels include fox (Sciurus niger), eastern gray (Sciurus carolinensis), western gray (Sciurus griseus), and tassel-eared (Sciurus aberti) squirrels.

Fox squirrels (Fig. 1) measure 18 to 27 inches (46 to 69 cm) from nose to tip of tail. They weigh about 1 3/4 pounds (787 g) to 2 1/4 pounds (1,012 g). Color varies greatly, from all black in Florida to silver gray with a white belly in Maryland. Georgia fox squirrels usually have a black face. Ohio and Michigan fox squirrels are grizzled gray-brown above with an orange underside. Sometimes several color variations occur in a single population. Eastern gray squirrels are also variable in color. Some have a distinct reddish cast to their gray coat. Black ones are common in some northern parts of their range. Eastern gray squirrels measure 16 to 20 inches (41 to 51 cm). They weigh from 1 1/4 pounds (567 g) to 1 3/4 pounds (794 g).

The western gray squirrel is gray above with sharply distinct white underparts. Size is similar to that of the eastern gray squirrel.

Tassel-eared squirrels are similar in size to gray squirrels and have several color phases. The most common is gray above with a broad reddish band down the back. Black tufted ears are their most distinguishing characteristic (the tufts are larger in winter, about 1 inch [2.5 cm]).

There are two species of pine squirrels: the red squirrel (Tamiasciurus hudsonicus) and Douglas pine squirrel (Tamiasciurus douglasii). Pine squirrels are 10 to 15 inches (25 to 38 cm) in total length and weigh 1/3 to 2/3 pounds (151 to 303 g). Red squirrels are red-brown above with white underparts. Douglas squirrels are gray-brown above with yellowish underparts. Both species have small ear tufts and often have a black stripe separating the dark upper color from the light belly.

Two species of flying squirrels occur in North America. The southern flying squirrel (Glaucomys volans) is 8 to 10 inches (20 to 25 cm) long. The northern flying squirrel (Glaucomys sabrinus) averages 2 inches (5 cm) longer. It can be difficult to distinguish between the two; both may be various shades of gray or brown above and lighter below. A sharp line of demarcation separates the darker upper color from the lighter belly. The most distinctive characteristics of flying squirrels are the broad webs of skin connecting the fore and hind legs at the wrists, and the distinctly flattened tail.

General Biology, Reproduction, and Behavior

Fox and gray squirrels breed when they are 1 year old. They breed in mid-December or early January and again in June. Young squirrels may breed only once in their first year. The gestation period is 42 to 45 days. During the breeding season, noisy mating chases take place when one or more males pursue a female through the trees. They nest in tree cavities, human-made squirrel boxes, or in leaf nests. Leaf nests are constructed with a frame of sticks filled with dry leaves and lined with leaves, strips of bark, corn husks, or other materials. Survival of young in cavities is higher than in leaf nests. Cavities are the preferred nest sites.

About 3 young comprise a litter. At birth they are hairless, blind, and their ears are closed. Newborns weigh about 1/2 ounce (14 g) at birth and 3 to 4 ounces (84 to 112 g) at 5 weeks. Young begin to explore outside the nest about the time they are weaned at 10 to 12 weeks. At weaning they are about half of their adult weight.

Home range size depends on the sea-son and availability of food. It may vary from 1 to 100 acres (0.4 to 40 ha). Squirrels move within their range according to availability of food. They often seek mast-bearing forests in fall and favor tender buds in elm and maple forests in the spring.

During fall, squirrels may travel 50 miles (80 km) or more in search of better habitat. Squirrel populations periodically rise and fall. During periods of high populations, squirrels—especially gray squirrels—may go on mass emigrations. At such times many animals die.

Fox and gray squirrels are vulnerable to numerous parasites and diseases. Ticks, mange mites, fleas, and internal parasites are common. Squirrel hunters often notice bot fly larvae (called “wolves” or “warbles”) protruding from the skin. These fly larvae do not impair the quality of the meat for eating. Squirrels are a food source for hawks, owls, snakes, and several mammalian predators. Predation seems to have little effect on squirrel populations.

Typically about half the squirrels in a population die each year. In the wild, squirrels over 4 years old are rare, while in captivity individuals may live 10 years or more.

The biology of other North American squirrels has much in common with that of fox and gray squirrels, although most other species have one breeding season per year. Flying squirrels are unique in that they are active at night. All other species are active during the day.


Tree Squirrels | Tree Squirrel Overview | Tree Squirrel Damage Assessment | Tree Squirrel Damage Management | Tree Squirrel Resources | Tree Squirrel Acknowledgments | ICWDM | Wildlife Species Information


Range

Figure 2. Fox squirrel ranges in North America

Fox squirrels occur in much of the eastern and central United States, as well as in several locations in the West, where they have been introduced (Fig. 2).

Figure 3. Eastern gray squirrel ranges in North America

Eastern gray squirrels have a similar range to that of fox squirrels but do not occur in many western areas of the fox squirrel’s range. They have been introduced in several locations in the West (Fig. 3). Western gray squirrels are confined to west coast states and a small portion of western Nevada (Fig. 3).

Figure 4. Pine squirrel ranges in North America

Pine squirrels occur across northern North America south into the Appalachians and Rockies, and on the west coast. Red squirrels are often associated with coniferous forests. The Douglas squirrel is restricted to the west coast from southwestern British Columbia south through the Sierras to northern Baja California (Fig. 4).

The tassel-eared squirrel is restricted to Ponderosa pine forests in the Southwest, usually at altitudes above 5,000 feet (1,500 m). It occurs in portions of Wyoming, Colorado, New Mexico, Arizona, and Utah (Fig. 2). The northern flying squirrel occurs across northern North America. Its range extends south into the Appalachians and Rockies. The southern flying squirrel occurs in the central and eastern United States (Fig. 5).

Figure 5. Tassel-eared squirrel ranges in North America

Habitat

Fox squirrels and gray squirrels inhabit the same kinds of forests, both hardwood and coniferous, over much of their range. Gray squirrels are more abundant where a high percentage of land is forested. In areas with 10% forest cover, fox and gray squirrel populations may be equal. Fox squirrels prefer oak-hickory habitat over much of their range, especially in the West. In Georgia and Florida, fox squirrels seem to prefer pine timber. The western gray squirrel prefers mixed hard-woods and conifers and dry open hardwoods. Tassel-eared squirrels are strongly associated with Ponderosa pine. Pine squirrels prefer coniferous forests but also occur in mixed conifer and hardwood forests, or sometimes in hardwood habitats.

Food Habits

Fox and gray squirrels have similar food habits. They will eat a great variety of native foods and adapt quickly to unusual food sources. Typically, they feed on mast (wild tree fruits and nuts) in fall and early winter. Acorns, hickory nuts, walnuts, and dosage orange fruits are favorite fall foods. Nuts are often cached for later use. In late winter and early spring they prefer tree buds. In summer they eat fruits, berries, and succulent plant materials. Fungi, corn, and cultivated fruits are taken when available. During population peaks, when food is scarce, these squirrels may chew bark from a variety of trees. They will also eat insects and other animal matter.

Pine squirrels are often heavily dependent on coniferous forests for cones and buds but will also eat a variety of other foods common to gray and fox squirrel diets. Douglas squirrels depend largely on Ponderosa pine for food. Flying squirrels’ food habits are generally similar to those of other squirrels. However, they are the most carnivorous of all tree squirrels. They eat bird eggs and nestlings, insects, and other animal matter when available. Flying squirrels often occupy bird houses, especially bluebird houses.


Jeffrey J. Jackson. Former Extension Wildlife Specialist. Warrell School of Forestry and Natural Resources. University of Georgia Athens, Georgia 30602

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