Squirrels are a familiar sight whether we live in a city, suburb, or rural setting. It’s fun to watch squirrels’ antics at bird feeders, their acrobatics on branches and utility wires, their furtive foraging for nuts and seeds. Because we often see them near our homes, we may forget that squirrels are wild animals and that they play an important role in the forest ecosystem. Tree squirrels are gatherers of seeds, planters of trees, and prey for predators like hawks and owls.
The Northeast is home to four species of tree squirrels, those that make their homes in tree branches. Two are well known – the eastern gray squirrel and the red squirrel – for they are diurnal, active in the daytime. Many people are surprised to learn that two species of flying squirrel – the northern and southern flying squirrels – live in our woods as well. Because they are nocturnal, it’s rare to get a glimpse of these elusive creatures, though in some places they are as numerous as other squirrels. Chipmunks are not included here because they are more closely related to woodchucks, marmots, and prairie dogs than to tree squirrels. They spend more of their time on or under the ground than in the branches of trees, and they are dormant in winter.
Whenever similar species come into close contact, there is an inevitable struggle for resources like food, shelter, and nest sites. The tree squirrels in our forests have enough differences in lifestyle to live side by side. Each has a special niche – particular habits and habitat preferences – that help it avoid conflicts with the other squirrels.
Red and gray squirrels are active in daytime and so we often see them. They are similar in appearance but differ in color and size. Red squirrels are smaller, typically about a foot long from nose to tip of tail, while gray squirrels may reach twenty inches. Red squirrels are reddish-brown with light undersides. Gray squirrels have salt-and-pepper fur on their backs, giving them a light gray color – though a black variant is found in some places, and some have a reddish tinge. The long, bushy tail of the gray squirrel is its most distinctive feature. The red squirrel’s tail, though less bushy, is just as important for balance, warmth, and body language. Come too close to a red squirrel’s territory and you will be greeted by angry chattering and tail waving!
The body plan of flying squirrels is similar to other tree squirrels with some notable differences. Most conspicuous is a special adaptation that allows the gliding flight for which they are named. A loose flap of skin, the patagium, extends from wrist to ankle. When the flying squirrel spreads its legs, the skin is drawn tight, allowing it to glide on the air. In the northern flying squirrel, the glide ratio has been measured at about two to one, which means it glides forward about two feet for every foot it drops downward. From a high perch, the flying squirrel can glide over 150 feet. Its flattened tail works like the tail on a kite, catching the air and creating drag. Its large eyes are an aid to nighttime activities – gliding, foraging, and evading owls. When it lands on a tree, it scurries to the back of the trunk, an adaptation to avoid aerial predators in pursuit.
Like other rodents, squirrels are primarily vegetarian, living on nuts, seeds, buds, fruits, and mushrooms. Their teeth and skulls are shaped like other gnawing herbivores, with chisel-like front teeth and flat, grinding molars. However, squirrels are also opportunists, eating foods in the realm of the carnivore such as insects, eggs, and nestling birds when available. Preferences for particular kinds of food help these four squirrels avoid competition. The gray squirrel collects nuts, the bulk of its diet being acorns, beech nuts, and hickory nuts. The red squirrel specializes in conifers, stripping the scales from spruce and pine cones to eat the seeds inside. A red squirrel’s favorite feeding site can be readily found by their large midden piles made of buried cones and cone scales, often at the base of an evergreen tree. It’s not surprising that gray squirrels prefer hardwood forests where nut-bearing trees are found, while red squirrels favor conifer forests. Flying squirrels relish the hard-to-find truffle, a kind of underground mushroom, but otherwise are generalists in what they eat and live in all of our forests. Because they forage at night, they avoid direct confrontations with the other kinds of squirrels.
Tree squirrels are active all winter and must “squirrel away” food for lean times. Each uses a slightly different technique. Eastern gray squirrels are scatter hoarders, burying nuts individually and scattering them all around their territory. This method reduces the chances of another animal finding the whole hoard, but it makes more work for the squirrels. They are very sly about hiding each item, digging fake holes at times, and moving nuts around frequently. Despite this, these squirrels have about an eighty-five percent success rate in retrieving their buried nuts. Red squirrels are larder hoarders, creating large caches of seeds or cones inside hollow trees or logs, in middens, or in underground burrows. In winter, they tunnel through the snow to reach these stockpiles. They also hang cones in shrubs for an easy winter meal. A mushroom or apple stuck in the fork of a branch – left there to dry for later storage – is a sure sign of red squirrels at work. Flying squirrels also create larders, often storing seeds and nuts in the same hollows where they den.
Finding shelter in the shared forest is not always easy, and competition for hollows in trees can be intense. The adaptable tree squirrel has other options at hand. Flying squirrels may put a roof on an old bird’s nest or build a small leaf nest of their own. In winter, they may share hollows, as many as twenty in a single den. Eastern gray squirrels often build large leaf and stick nests, high in the branches of trees. These nests, called dreys, may be used year-round. Red squirrels are also adept nest builders, weaving strips of bark and leaves into suitable shelters in conifer trees, or they may dig burrows underground.
In winter, squirrel tracks are a common sight, for tree squirrels move easily from canopy to forest floor: four prints, a space, four more prints, and so on. The front feet land side by side and then the back feet swing forward, landing ahead of the front feet. A rabbit pattern is similar, but a rabbit’s front feet land one ahead of the other rather than side by side. When tracks mysteriously end at a tree trunk, think squirrel! Following squirrel tracks in the snow can tell us much about their busy lives.
Tree squirrels play an important role in the forest ecosystem as prey for many predators, especially aerial ones like hawks and owls. They also shape the forest they live in by planting the seeds of their food trees. A forgotten acorn becomes an oak that provides food and shelter for many different forest creatures.
The tree squirrels’ tale is one of similar species living side by side in the forest but avoiding competition through specialization. Each occupying its own particular niche in the ecosystem, red, gray, and flying squirrels share and shape the forests in which they live.
Suggested Reading
Long, Kim. Squirrels. Johnson Nature Series. Boulder: Johnson Books, 1995.
Murie, Olaus J. A Field Guide to Animal Tracks. Peterson Field Guide Series. Boston: Houghton Mifflin Co., 1974.
Rezendes, Paul. Tracking and the Art of Seeing. 2nd edition. New York: Harper Collins, 1999.
Stokes, Donald and Lillian Stokes. Stokes Guide to Animal Tracking and Behavior. Boston: Little, Brown and Co., 1986.
Nearby Nature 