Squirrels and relatives I

Flying squirrels (Pteromyinae)

Class: Mammalia

Order: Rodentia

Suborder: Sciurognathi

Family: Sciuridae

Subfamily: Pteromyinae

Thumbnail description
Small to medium rodents with large bushy tails often dorso-ventrally flattened; all species possess furred gliding membranes connecting the fore and hind limbs

Size
5–48 in (13–122 cm); 0.7–5 lb 8 oz (20–2,500g)

Number of genera, species
14 genera; 43 species

Habitat
Forest, woodlands, plantations, parkland, and cliffs

Conservation status
Critically Endangered: 2 species; Endangered: 4 species; Vulnerable: 1 species; Lower Risk/Near Threatened: 11 species

Distribution
Northern Europe, north, south, and southeast Asia, and North America

Evolution and systematics

The subfamily Pteromyinae is generally considered to be one of the two subfamilies of squirrels (Sciuridae). It has been considered by some authors to be a monophyletic sister family, the Pteromyidae to the Sciuridae, while others have questioned its monophyly and subfamily status. There is a uniformity of characters among all its members, which are adapted for a nocturnal, gliding lifestyle. All squirrels are thought to be derived from a common arboreal rodent ancestor, Protosciurus, rather similar in structure to modern-day tree squirrels such as Sciurus.

There are 43 species of flying squirrel grouped into 14 genera. Some of these species are still very poorly known and three species are known only from their type localities; a further nine have very restricted mainland or small island endemic distributions.

Physical characteristics

Flying squirrels are small to medium rodents highly adapted for an arboreal lifestyle. They are generally slim and leggy animals with large bushy tails, which often makes them appear larger than they actually are. All species are adapted for gliding with membranes of muscle running along the sides of the body between the front and hind legs, in some genera, such as the giant flying squirrels (Petaurista), these extend up the neck and right down to the base of the tail. A rod of cartilage connected to the wrist is used to extend the gliding membrane. In most species the tail is flattened dorso-ventrally to assist in gliding and directional control.

They have large eyes and generally small but obvious ears. The fur is very soft and dense in all species. They are paler below with generally brown, gray, or blackish upper parts, although the giant flying squirrels are highly variable with some populations being brightly colored—vivid orange above and yellow below.

Distribution

Flying squirrels are most diverse in south and southeast Asia especially in tropical forest. Fifteen species are island endemics, 11 endemic to Indonesian islands, two to the Philippines, and a further two to Japan. Three species occur in northern temperate regions—the distribution of two of which extends right up to the Arctic Circle, northern flying squirrel (Glaucomys sabrinus) and Siberian flying squirrel (Pteromys volans). Northern flying squirrel and southern flying squirrel (Glaucomys volans) are the sole representatives of the group in the New World.

Habitat

Flying squirrels are arboreal and found in a variety of forested or wooded areas including northern boreal forest, temperate deciduous forest, and tropical rainforest. Some species also occur within plantations and parkland. Two species, the woolly flying squirrel (Eupetaurus cinereus) and complex-toothed flying squirrel (Trogopterus xanthipes), live at high altitudes on rocky cliffs and outcrops. All species are nocturnal and many very seldom come down to the ground. They nest in a variety of tree holes, crevices or nests that they either construct themselves or occupy built by other species.

Behavior

All species of flying squirrel are totally nocturnal. They display a variety of social systems. Giant flying squirrels are believed to be largely monogamous, occurring in pairs both in and outside the breeding season. Most species though are largely territorial, although this territoriality may breakdown in the temperate species outside of the breeding season, when large groups communally nest in winter dens.

Home ranges of up to 12 acres (5 ha) have been reported in giant flying squirrels and 6 acres (2.5 ha) in southern flying squirrel. Information on the small tropical species is sparse despite some of them being fairly numerous. Their gliding ability is very precise and individuals can change direction in mid-flight, the giant flying squirrels have been reported as gliding up to 1,475 ft (450 m). Many species are naturally very docile and do not attempt to bite when handled. Flying squirrels have a variety of vocalizations including loud high-pitched bird-like trills and soft twittering calls.

Feeding ecology and diet

Flying squirrels feed on a variety of plant and animal matter. Many of the larger tropical species are mainly herbivorous; some specializing on the feeding of young shoots and fruits. The temperate species tend to feed largely upon tree seeds, some fruits and fungi, and animal matter. Smaller tropical species tend to be much more carnivorous, feeding upon insects, spiders, and even small vertebrates. The montane woolly flying squirrel feeds upon mosses and lichens on rocks and conifer needles.

They are known to glide large distances to particular trees in order to feed on seasonal fruits or tender growing leaves. Some species show considerable seasonal variation within their diet, exploiting food resources as they become available.

Reproductive biology

The breeding biology of most species is poorly known or totally undescribed. The tropical species of flying squirrel breed aseasonally while those from temperate regions have short and clearly defined summer breeding seasons. One litter per year is normal for most species; although Glaucomys has been reported to have two litters, while the aseasonal Hylopetes is highly variable with as long as 17 months between litters.

Most species give birth to small litters, typically only one or two young. A few of the smaller species have larger litters and southern flying squirrel can produce up to seven young. The young are generally small at birth and all but one genus produces offspring that are blind and naked or very sparsely furred at birth. The exception is the dwarf flying squirrels (Petinomys) that give birth to comparatively large, fully furred offspring with their eyes open. These infants can climb and start to eat solids when only one day old. In Glaucomys, gestation is around 40 days and weaning occurs around eight weeks of age, but young will stay with the mother longer if a second litter is not produced.

Conservation status

Flying squirrels suffer heavily from habitat loss due to deforestation for development and agriculture. The larger species are also hunted locally for food and some species are hunted for their fur or as pests of plantations. In 2002, 18 species are considered threatened or Near Threatened by the World Conservation Union (IUCN), and a further four sub-species are also considered to be at risk.

Significance to humans

Most species of flying squirrel are highly cryptic and even when living in populated areas often go completely unnoticed by humans. Giant flying squirrels are hunted for food across parts of their range and can become pests of fruit crops in some plantations.

Species accounts

Resources

Corbet, G. B., and J. E. Hill. The Mammals of the Indomalayan Region: A Systematic Review. Oxford and New York: Oxford University Press, 1992.

Forsyth, A. Mammals of North America: Temperate and Arctic Regions. Willowdale, Canada: Firefly Books Ltd., 1999.

Gurnell, J. The Natural History of Squirrels. London: Christopher Helm, 1987.

Nowak, R. M. Walker's Mammals of the World. 6th ed. Baltimore and London: Johns Hopkins University Press, 1999.

Wilson, D. E., and D. M. Reeder, eds. Mammal Species of the World: A Taxonomic and Geographic Reference. 2nd ed. Washington, DC: Smithonian Institution Press, 1993.

[Article by: Mike J. R. Jordan, PhD]