Wildlife Species Guide
Southern Flying Squirrel
<< Back to Index |Description | Habits | Reproduction | Management |
The southern flying squirrel (Glaucomys volans) is found
throughout the deciduous forests of eastern North America from
southern Ontario to the Gulf Coast, with isolated populations in Mexico
and as far south as Honduras. Its distribution in North America is more
southerly than that of its close relative, the northern flying squirrel
(Glaucomys sabrinus). The northern variety is found primarily in coniferous forests in most
of Canada and in the northern United States from Maine to California. The ranges of the
two species overlap in some parts of the north-central and
northeastern United States. Although the northern flying squirrel is larger,
the southern variety is more aggressive and tends to be dominant.
Only the southern flying squirrel is found in Nebraska, and it is found
only in remnant tracts of eastern deciduous forest in the southeastern
corner of the state. It is known to occur in the forested bluffs along the
Missouri River from the far southeastern corner of the state north
to about Nebraska City. Historically, it probably occurred over a wider
area when the deciduous forest in the state was more extensive than it
is today. Although the southern flying squirrel is considered
threatened in Nebraska and is fully protected, it is quite common in
many eastern states.
The southern flying squirrel is easily distinguished from other
Nebraska tree squirrels by its smaller size and by its gliding membrane, or
patagium, a fold of skin that extends from the wrist of the front leg to the
ankle of the hind leg. When the front and hind legs are extended, the
membrane forms a wing-like gliding surface. The furred, broad and
horizontally flattened tail serves as a rudder and stabilizer during glides.
The eyes are noticeably large, an adaptation for its nocturnal habits.
The ears are more prominent than in other tree squirrels. Whiskers are
Southern flying squirrels are quite small. Adults usually are nine to 10
inches long including the tail, and they weigh between two and four
ounces. Their fur is soft, silky and moderately long. The upper body is
grayish to brownish in color, and the underparts are creamy white. The
eyes are surrounded by a black ring, and a black border extends along the
edge of the gliding membrane.
Flying squirrels produce several vocalizations including a high
pitched "tseet" and other chirping sounds. Some vocalizations are
above the frequency range of the human ear. Some researchers have
speculated that flying squirrels use high-pitched sounds for navigation,
similar to the echolocation system of bats. Although flying squirrels have
an excellent sense of hearing, they do not have the highly specialized
hearing system of bats, and echo location is unlikely.
Undoubtedly the most unusual habits of the southern flying squirrel
are its gliding ability and its nocturnal behavior. unlike fox squirrels or
gray squirrels that are active by day, the southern flying squirrel is probably
the most nocturnal of all mammals in Nebraska. Other gliding
mammals from various parts of the world also tend to be nocturnal, and
a possible explanation for this association is that gliding in daylight
might attract the attention of hawks or other diurnal (daytime) predators.
The gliding of a flying squirrel is spectacular. Glides begin after the
squirrel climbs to a lofty treetop perch and assesses the landing site
by moving its head up and down and from side to side, apparently triangulating
to judge distance. It then launches itself with all four legs extended at
right angles from the body, stretching the flying membrane.
With tremendous agility, flying squirrels can steer around branches
or other obstacles. Most steering is done with the tail, but squirrels also
vary the tension on the membrane to steer and to control speed. They
usually land on the vertical trunk of another tree, invariably upright with
the hind feet touching first.
Upon landing, they scurry to the opposite side of the tree to elude any
pursuing predator. Glides occasionally extend for more than 50 yards, but
are usually much shorter. Flying squirrels appear to have a maximum
gliding ratio of about three horizontal feet for every vertical foot, a
glide ratio that would allow them to travel the length of a football field
from a perch 100 feet high.
Southern flying squirrels do not hibernate, although they may remain
in their nests for several days during severe winter weather. In winter they
form groups in a common nest to conserve warmth. The number of
animals in the winter congregations varies by latitude, with larger con-
gregations found in northern climates. One tree cavity in Illinois
was reported to contain 50 squirrels. In Nebraska, eight squirrels have
been found in one nest box.
The population density of flying squirrels depends on the quality of
the habitat. In favorable habitat, densities can approach five squirrels per
acre. Estimates of home range size, the area used for normal day-to-day
activities, range from about one acre to five acres. Females defend their
home range, at least during parts of the year, and there is little or no over
lap with the home range of other females. Males do not defend
territory, and their home ranges often overlap with those of other males.
Southern flying squirrels show two periods of breeding activity. The
first is in February and March, and the other is from late May through
July. Females can produce two litters per year but only under favorable
conditions. Litters, usually of three or four, but up to seven young, are
born following a gestation period of 40 days.
Newborn young are hairless with eyes and ears closed. They are tiny,
weighing less than a quarter-ounce each. The gliding membrane is
visible as a transparent fold of skin. The ears open at
about three weeks of age, and a week later the eyes open. The
young are weaned at six to eight weeks and are capable of gliding
soon thereafter. Young typically remain with the female until the
birth of the next litter.
Adults are sometimes seen together as pairs, but males typically
leave females before the young are born and do not assist in caring for
the young. The females are devoted parents. They seldom leave the new-
born young, defend them rigorously and will move the young to a new
nest if disturbed. An accumulation of parasites in the nest may cause the
female to move the young even if no other disturbances are present.
Flying squirrels reach sexual maturity at about one year. They do
not form tight pair-bonds. Females frequently have different mates in
subsequent breeding seasons.
Southern flying squirrels are primarily vegetarian, but will occasionally
eat animal foods. Nuts, primarily acorns and hickory nuts,
are preferred foods and make up the bulk of the diet. Flying squirrels will
also consume various seeds, fruits, berries, mushrooms, buds, flower
blossoms and tree bark. Animal items that occasionally may be eaten
include insects, bird eggs and nestlings, small nestling mammals, carrion,
and adult shrews and mice.
Nuts are gathered and stored as winter approaches. The shortening
of day length rather than temperature triggers the urge to store food. Nuts
are buried individually or are cached in nest cavities or other cracks and
crevices in trees. Several hundred nuts can be stored in a night. In good
nut-production years, the stored nuts carry the squirrels through the winter
and even into spring and summer. Nuts are eaten in a characteristic pattern.
Flying squirrels usually cut a fairly smooth circular or oval opening on
the side or end of a nut. On larger, heavy-shelled nuts they will make
a second opening or remove an entire end in a single cut. Other tree
squirrels usually crush nuts without leaving the shells intact.
The feeding pattern of flying squirrels more closely resembles that
of deer mice or white-footed mice, which also inhabit cavities and nest
boxes in southeastern Nebraska, but these species usually do not eat
large, heavy-shelled nuts, and their tooth marks are finer. Flying squirrels
will accept a "helping hand" by visiting bird feeders where they
consume seeds, suet and peanut butter.
ln broad terms, southern flying squirrels require deciduous forests as
habitat. Specifically, they require mast-producing trees such as oaks,
hickories and walnuts for food, cavities in dead or live trees for
shelter or and some form of water.
Cavities used by flying squirrels are often constsructed by woodpeckers,
although any natural or artificially constructed cavity with an
entrance hole larger than one inch in diameter might be used. Cavities
are typically lined with strips of inner bark and leaves, but lichens,
moss, feathers and other materials have been incorporated into nests.
Cavities are used throughout the year. Flying squirrels inhabit a
primary nest cavity that is used more or less continuously and one or
more secondary nest cavities used as feeding stations or as a refuge if
the primary nest is disturbed. Outside leaf nests are seldom used in
Northern climates, but are fairly common in warmer areas.
The water requirements of flying squirrels are not well understood. They
obviously obtain some water from their food. Free-standing water
is consumed when available, but their range is not limited to areas
with available surface water. Where surface water is not available, squirrels
appear to be physiologically adapted and get sufficient water
from food, dew and rains. They probably make use of water that temporarily
collects in tree cavities.
Flying squirrels have been known to live 13 years in captivity, but seldom
live five years in the wild. A variety of predators and internal and
external parasites can affect them. Predators include owls, domestic
cats, hawks, snakes, bobcats, raccoons, weasels and foxes. Predation
is probably no more significant for flying squirrels than it is for other
tree squirrels. External parasites reported from flying squirrels
include fleas, lice and mites, and internal parasites include nematodes and
protozoans. None of those parasites are known to be substantial limiting
factors. Few diseases have been reported in flying squirrels, and none
are thought to be significant.
The amount and quality of habitat are probably the most important
factors limiting flying squirrel populations in Nebraska. The range of the
southern flying squirrel coincides closely with the range of several
species of oaks and hickories. Eastern Nebraska is near the western
edge of distribution of several oak and hickory species and the southern
flying squirrel. Because many of the mast-producing trees produce nut
crops irregularly, a diversity of tree species is needed to assure an ample
supply of nuts each year, and the lack of diversity of mast-producing
trees may be a limiting factor for flying squirrels.
Although Nebraskans have little control over the natural diversity of
mast-producing trees, the loss of habitat can be controlled. The
primary reason the southern flying squirrel is threatened in Nebraska is
the loss of deciduous timber habitat and the potential for this loss to
continue. Habitat has been lost for several reasons. The conversion of
forest to cropland and the use of forested Missouri River bluffs for
homesites are the two most significant. Researchers from Peru
State College found that 42 percent of the timber in Nemaha County was
lost from 1856 to 1977. Most of the loss has occurred since 1955,
primarily through conversion to cropland.
Changes in the remaining forested areas can be detrimental to
flying squirrels. Logging removes mature oak timber that is important
to flying squirrels as a food source and for the cavities the trees contain.
Removal of trees for firewood can be detrimental because dead trees
containing cavities are often cut, and the best mast-producing species are
also the best species for firewood.
Management and Outlook
Because flying squirrels are nocturnal and are not valued as a game
species, they have not been studied as extensively as other tree squirrels.
Much of our knowledge about flying squirrels has been gained from observing
them in captivity. Flying squirrels are doing well without human assistance in
areas of their range where habitat is abundant. Management practices have rarely
been implemented specifically to benefit flying squirrels.
Flying squirrels readily use nest boxes placed for their benefit or for
other species. Nest boxes have been used in Nebraska and other areas in
attempts to determine the status and distribution of flying squirrels. By
periodically checking nest boxes and capturing and tagging the inhabitants,
considerable information can be gathered. The number of squirrels
using an area and their survival can be estimated, and movements can be
monitored. Nest boxes can be used as a management tool when a
shortage of cavities exists. Such a situation can occur in a young
timberstand where trees are old enough to produce mast, but cavities are in
Nebraska can never expect large populations of flying squirrels unless
the loss of habitat is dramatically reversed and forested areas are expanded.
However, flying squirrel populations could increase. First,
wholesale conversion of eastern Nebraska woodlands to cropland
would have to cease. The effects of commercial logging or firewood cutting
can be moderated by leaving a few large dead trees. The effects of
homesites might not be serious if tree removal is minimized.
Homeowners should consider erecting nest boxes and feeders and
should keep pets from ranging freely If the loss of mature deciduous
timber in southeastern Nebraska can be reversed, natural plant succession
will eventually replace some of the lost habitat. Through natural succession,
remaining woodlands and pastures would eventually become
mature oak-hickory forest-just what the flying squirrel needs. The
future of the species in Nebraska would then be brighter.