Squirrels and Relatives I: Flying Squirrels (Pteromyinae)
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
List of Species
Red giant flying squirrelSouthern flying squirrel
Siberian flying squirrel
Hose's pygmy flying squirrel
Red giant flying squirrel
Petaurista petaurista
taxonomy
Petaurista petaurista (Pallas, 1766), no locality stated, likely western Java, Indonesia. The number of subspecies is uncertain; it is highly variable in color and size across its range.
other common names
None known.
physical characteristics
Head and tail length 35–48 in (89–122 cm); weight 2.3–5.5 lb (1,050–2,500 g). Fur has a mahogany-red coloring, and the gliding membrane is thickly haired.
distribution
Afghanistan east through south and Southeast Asia down to Sumatra, Java, and Borneo.
habitat
Forest and plantations often at altitudes above 2,250 ft (750 m).
behavior
Nocturnal, seldom coming to the ground and gliding large distances between trees for feeding.
feeding ecology and diet
Shoots, leaves, and fruits.
reproductive biology
Generally monogamous and giving birth to one or two young. Young develop slowly and are not weaned until about 3 months old.
conservation status
A widespread species, although some highly distinctive populations are locally threatened.
significance to humans
Hunted for food and fur across parts of its range.
Southern flying squirrel
Glaucomys volans
taxonomy
Glaucomys volans (Linnaeus, 1758), Virginia, United States. Ten subspecies are recognized.
other common names
None known.
physical characteristics
Head and tail length is 8–10 in (20–25 cm); weight 1.5–3.5 oz (45–100 g). Upperparts are gray and underparts are white.
distribution
Eastern Canada south through the eastern United States, fragmented populations stretching down to Honduras.
habitat
Predominantely deciduous forest.
behavior
Nocturnal, normally territorial when breeding but nests communally during the winter.
feeding ecology and diet
Nuts, seeds, and insects.
reproductive biology
Serially monogamous. Breeds in spring and early summer, up to two litters of 2–7 young produced following a 40 day gestation period.
conservation status
Generally common but some smaller fragmented populations threatened by habitat loss.
significance to humans
Sometimes encouraged to feeding tables and also kept as a pet.
Siberian flying squirrel
Pteromys volans
taxonomy
Pteromys volans Linnaeus, 1758, "in borealibus Europae, Asiae, et Americae." Seven subspecies are recognized.
other common names
English: Russian flying squirrel.
physical characteristics
Head and tail length is 9–13.5 in (23–35 cm); weight 3–5 oz (80–150 g). Upperparts are yellow-gray to blackish gray in summer and silvery gray in winter. Underparts are white.
distribution
Northern Palaearctic, from Finland east through Siberia and south to Mongolia, northern China and Korea, also Hokkaido.
habitat
Mature mixed deciduous and coniferous forest.
behavior
Nocturnal and highly arboreal. Nests communally during the winter.
feeding ecology and diet
Seeds, nuts, leaves, catkins, invertebrates and possibly even nestlings.
reproductive biology
Information on mating behavior is incomplete. One or two litters produced each year of normally 2–3 young.
conservation status
Declining across much of its range and protected within Europe. Considered Lower Risk/Near Threatened by the IUCN.
significance to humans
Sometimes nests within buildings, hunted for fur in some parts of Russia.
Hose's pygmy flying squirrel
Petaurillus hosei
taxonomy
Petaurillus hosei (Thomas, 1900), eastern Sarawak, Malaysia. No subspecies recognized.
other common names
None known.
physical characteristics
Head and body length is 6.5 in (17 cm); weight 0.9 oz (25 g). Upperparts are fawn to pale rufous, cheeks are pale buff, and underparts are white.
distribution
Borneo.
habitat
Lowland tropical forest and forest edge.
behavior
Nocturnal, several reported to nest together.
feeding ecology and diet
Unknown, but probably insectivorous.
reproductive biology
Nothing is known.
conservation status
Not threatened.
significance to humans
None known.
| Common name / Scientific name | Physical characteristics | Habitat and behavior | Distribution | Diet | Conservation status |
| North Chinese flying squirrel Aeretes melanopterus | Short, dense, soft fur, dull brownish in color with a slate base. Hairs on side of body have yellowish tips. Underparts are gray to buff, throat and ventral surface are whitish. Gliding membrane is dark brown, head is pale and grayer than back. Tail is bushy with black tip. | Species inhabits forests. Other information is unknown. | Hebei and Sichuan, China. | Diet unknown, but most likely fruits, nuts, and leaves. | Lower Risk/Near Threatened |
| Black flying squirrel Aeromys tephromelas | Coloration of upperparts is dark brown to black, underparts are grayish brown. Long, slender, round tail is same color as back. Cheeks lack whiskers, ears are moderate in size. Head and body length 10–16.8 in (25.5–42.6 cm), tail length 11–20.7 in (28–52.7 cm), weight 39.8– 44.1 oz (1,128–1,250 g). | Mature forests or clearings with a few large trees. They are chiefly nocturnal and spend days curled up in high holes. | Malaysian region, except Java and south-western Philippines. | Fruits, nuts, leaves, and probably some insects. | Not threatened |
| Thomas's flying squirrel Aeromys thomasi | Coloration of upperparts is dark brown to black, underparts are grayish brown. Long, slender, round tail is same color as back. Cheeks lack whiskers, ears are moderate in size. Head and body length 10–16.8 in (25.5–42.6 cm), tail length 11–20.7 in (28–52.7 cm), weight 48.7– 52.5 oz (1,380–1,490 g). | Mature forests or clearings with a few large trees. They are chiefly nocturnal and spend days curled up in high holes. | Borneo, except the southeastern region. | Fruits, nuts, leaves, and probably some insects. | Not threatened |
| Hairy-footed flying squirrel Belomys pearsonii | Top of head and back are glossy reddish brown. Fur is fine, soft, and fairly long. Gliding membrane is dark brown, sparsely washed with red. Hands are reddish brown, underparts are light red to white. No cheek whiskers, feet are covered with long hair, small ears. Head and body length 7–10.2 in (17.8–26 cm), tail length 4–22.8 in (10.2–58 cm). | Dense, temperate, broad-leaved forests from 4,920 to 7,870 ft (1,500–2,400 m) in elevation. Not a particularly good glider. | Sikkim and Assam, India, to Hunan, Sichuan, Yunnan, Guizhou, Guangxi, and Hainan, China; Bhutan; Taiwan, Indochina, and northern Myanmar. | Fruits, nuts, leaves, and probably some insects. | Lower Risk/Near Threatened |
| Namdapha flying squirrel Biswamoyopterus biswasi | Upperparts are red grizzled with white, hands and feet are darker, underparts are white. Tail is pale smoky gray, changing into russet. Tail is cylindrical. Head and body length 15.96 in (40.5 cm), tail length 23.8 in (60.5 cm). | Single species was found at an elevation of 1,150 ft (350 m). Nothing known of reproductive or behavioral patterns. | Known only from type locality, western slope, Patkai Range in India. | Unknown, most likely fruits, nuts, and leaves. | Critically Endangered |
| Woolly flying squirrel Eupetaurus cinereus | Body is covered with thick, soft, woolly fur that is dark gray above and paler underneath. Long, trumpet-shaped muzzle. Claws are blunt. Head and body length 20.3–24 in (51.5–61.0 cm), tail length 15–18.9 in (38–48 cm). | Rocky terrain in mountainous regions. Little known of reproductive and behavioral patterns. | High elevations from northern Pakistan and Kashmir to Sikkim. | Unknown, most likely fruits, nuts, and leaves. | Endangered |
| Gray-cheeked flying squirrel Hylopetes lepidus | Fur is soft, dense, moderately long. Upperparts are grayish with a tinge of brown or yellow. Bright reddish brown, glossy brownish to black across hips and tail. Underparts are white, gray, or yellow. Ears are large and bluntly pointed, claws are short and blunt, tail is flat and tapers at tip. Head and body length 4.3–13 in (11–33 cm), tail length 3.1–11.5 in (8– 29.2 cm). | Various kinds of forest, as well as clearings and cultivated areas, from about 490 to 11,480 ft (150–3,500 m) in elevation. Arboreal and nocturnal. | Southern Vietnam, Thailand to Java; and Borneo. | Mainly fruits, but also nuts, tender shoots, leaves, and, apparently, insects and small snakes. | Not threatened |
| Javanese flying squirrel Iomys horsfieldii | Upper surface of gliding membrane is bright russet, underparts are grayish to pale orange. Tail is brownish above and chestnut underneath. Large, broad, naked ears. Head and body length 5.7– 9.1 in (14.6–23.1 cm), tail length 6.3– 8.3 in (15.9–21 cm), weight 4.2–8.1 oz 120–231 g). | Forests and plantations at all elevations. Build leaf nests. Litter size ranges from one to four offspring | Malay Peninsula to Java; and Borneo. | Unknown, most likely fruits, nuts, and leaves. | Not threatened |
| Common name / Scientific name | Physical characteristics | Habitat and behavior | Distribution | Diet | Conservation status |
| Whiskered flying squirrel Petinomys genibarbis | Broad, low head with short muzzle. Fur is dense and soft above, thin on lower parts. Coloration of upperparts varies from brown to black, underparts range from white to dark slate. Tail may be buff, darker towards tip. Head and body length 3.6–16 in (9.2–40.6 cm), tail length 3.3–11.5 in (8.5–29.2 cm), weight 3.9 oz (110 g). | Tropical forests up to 3,970 ft (1,210 m) in elevation. Nocturnal, good climbers. | Malaya to Sumatra, Java, and Borneo. | Nuts, fruits, young twigs, tender shoots and leaves, possibly the bark of certain trees, and perhaps some insects. | Not threatened |
Resources
Books
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.
Mike J. R. Jordan, PhD