Northern Flying Squirrel
by Eileen Dowd Stukel
Originally published in the March/April 1994 edition of SD Conservation Digest.
A charming but rarely-seen inhabitant of the Black Hills is the northern flying squirrel--charming enough to have earned the nickname "fairy diddle," rarely seen because it is almost entirely nocturnal, or active at night.
The northern flying squirrel is one of four tree squirrels found in South Dakota. The others are the fox squirrel, found nearly statewide, the gray squirrel, which inhabits a few sites in extreme northeastern South Dakota, and the red squirrel, which, like the flying squirrel, inhabits the Black Hills.
Nearly three dozen flying squirrel species are found worldwide, but only two in North America. The southern flying squirrel lives in eastern woodlots or forests of deciduous trees or mixtures of coniferous and deciduous trees. Its range adjoins and in some places overlaps that of the northern flying squirrel, which is found in dense coniferous or mixed forests of Canada and the northern and western United States. Some populations of northern flying squirrels are separate from the main population. These disjunct populations are found in the Black Hills, the southern Appalachians, the southern Rockies, the Sierra Nevadas, and on a few Canadian islands. Northern flying squirrels are slightly bigger and darker and have thicker fur than their southern counterparts.
Flying squirrels measure eight to eleven inches long and weigh only a few ounces. They are gray above and white underneath. They have large eyes and ears. A typical lifespan is four to six years, with most breeding at two years of age. Flying squirrels are not as vocal as other tree squirrels, usually uttering a soft chirp or "chuck."
Flying squirrels, though colorfully named, do not actually fly, but glide. A gliding membrane extends from the outside of each wrist to the ankle of each hind leg. Bony spurs project from the wrist to support and extend the membranes. A flying squirrel typically leaps from high in a tree, gliding twenty to thirty feet to a landing spot. It drops about one foot for each two feet of glide. During the glide, the animal changes speed and direction by varying slack in its flying flaps. A broad, flattened tail helps steer the glide, in which squirrels can make a ninety-degree turn. A flying squirrel lands hind feet first, with all four feet padded for shock absorption.
Their food habits are surprisingly diverse. The predominantly vegetarian diet includes mushrooms, lichens, fungi, nuts, seeds, fruits, and tree buds and blossoms. Their fondness for tree sap has led to the drowning of many flying squirrels in sap-collecting buckets. In fact, flying squirrels may drown in any water or sap source that has no means of escape. They also eat bird eggs and nestlings, many insects and their larvae, and carrion, or dead animals.
Northern flying squirrels build a cozy nest, usually in an abandoned woodpecker cavity at least ten to fifteen feet aboveground. The nest is lined with moss, shredded bark, feathers, pine needles, fur, or leaves. The female gives birth in May or June to three or four young, after a gestation of 40 days. The young are helpless at birth and their eyes don't open until they are four weeks old. The female cares for her young alone for a relatively long time, since young flying squirrels aren't weaned until they are eight weeks old. Even then, the bond remains. A female and her litter may stay together until the birth of her next litter the following year.
Although not as energetic at stashing food as other tree squirrels, flying squirrels gather and store nuts and seeds in nests, hammer them into tree forks, or bury them in the ground. They usually don't venture far from trees, but they will forage on the ground and retrieve buried food. Flying squirrels are most active after sundown and before sunrise. They will use cover of conifer branches and fallen logs to travel on the ground, and may hop on their hind feet when carrying a large food item.
Northern flying squirrels do not hibernate, but survive extreme cold by huddling together in their insulated nests. A winter huddle may include a female and her young, or an unrelated mixture of squirrels. In the northern parts of the species' range, as many as two dozen flying squirrels may nestle together for warmth.
Flying squirrels may use nest boxes intended for other animals, such as wood ducks, screech owls, or house wrens, provided the entrance hole is at least 1 1/4 inches wide. They also make nightly visits to bird feeders, particularly if offered sunflower seeds or peanut butter. They quickly acclimate to lighting used to enhance viewing of this special visitor.
Northern flying squirrels are found in all Black Hills counties in South Dakota. Little is known of their habitat preferences, but they have been observed in forests of spruce, pine, and oak, particularly near recently-burned areas. Forest management for flying squirrels includes conserving snags for nest cavities, sustaining a mixture of tree species in patches for squirrel travel corridors, and maintaining diverse plant communities to accommodate this animal's varied diet. If you discover a northern flying squirrel nest, please contact the South Dakota Natural Heritage Program. If lucky enough to glimpse the fairy diddle, you too are likely to be charmed by this character.