RODENTS: Squirrels, Tree
In this chapter tree
squirrels are divided into three groups: large tree
squirrels, pine squirrels, and flying squirrels. Large
tree squirrels include fox (Sciurus niger),
eastern gray (Sciurus carolinensis), western gray
(Sciurus griseus), and tassel-eared (Sciurus
Fox squirrels (Fig. 1)
measure 18 to 27 inches (46 to 69 cm) from nose to tip
of tail. They weigh about 1 3/4 pounds (787 g) to 2 1/4
pounds (1,012 g). Color varies greatly, from all black
in Florida to silver gray with a white belly in
Maryland. Georgia fox squirrels usually have a black
face. Ohio and Michigan fox squirrels are grizzled
gray-brown above with an orange underside. Sometimes
several color variations occur in a single population.
Eastern gray squirrels are
also variable in color. Some have a distinct reddish
cast to their gray coat. Black ones are common in some
northern parts of their range. Eastern gray squirrels
measure 16 to 20 inches (41 to 51 cm). They weigh from 1
1/4 pounds (567 g) to 1 3/4 pounds (794 g).
The western gray squirrel
is gray above with sharply distinct white underparts.
Size is similar to that of the eastern gray squirrel.
Tassel-eared squirrels are
similar in size to gray squirrels and have several color
phases. The most common is gray above with a broad
reddish band down the back. Black tufted ears are their
most distinguishing characteristic (the tufts are larger
in winter, about 1 inch [2.5 cm]).
There are two species of
pine squirrels: the red squirrel (Tamiasciurus
hudsonicus) and Douglas pine squirrel (Tamiasciurus
douglasii). Pine squirrels are 10 to 15 inches (25 to 38
cm) in total length and weigh 1/3 to 2/3 pounds (151 to
303 g). Red squirrels are red-brown above with white
underparts. Douglas squirrels are gray-brown above with
yellowish underparts. Both species have small ear tufts
and often have a black stripe separating the dark upper
color from the light belly.
Two species of flying
squirrels occur in North America. The southern flying
squirrel (Glaucomys volans) is 8 to 10 inches (20 to 25
cm) long. The northern flying squirrel (Glaucomys
sabrinus) averages 2 inches (5 cm) longer. It can be
difficult to distinguish between the two; both may be
various shades of gray or brown above and lighter below.
A sharp line of demarcation separates the darker upper
color from the lighter belly. The most distinctive
characteristics of flying squirrels are the broad webs
of skin connecting the fore and hind legs at the wrists,
and the distinctly flattened tail.
Fox squirrels occur in
much of the eastern and central United States, as well
as in several locations in the West, where they have
been introduced (Fig. 2).
Eastern gray squirrels
have a similar range to that of fox squirrels but do not
occur in many western areas of the fox squirrel’s range.
They have been introduced in several locations in the
West (Fig. 3).
Western gray squirrels are
confined to west coast states and a small portion of
western Nevada (Fig. 3).
Pine squirrels occur
across northern North America south into the
Appalachians and Rockies, and on the west coast.
Red squirrels are often
associated with coniferous forests. The Douglas squirrel
is restricted to the west coast from southwestern
British Columbia south through the Sierras to northern
Baja California (Fig. 4).
The tassel-eared squirrel
is restricted to Ponderosa pine forests in the
Southwest, usually at altitudes above 5,000 feet (1,500
m). It occurs in portions of Wyoming, Colorado, New
Mexico, Arizona, and Utah (Fig. 2).
The northern flying
squirrel occurs across northern North America. Its range
extends south into the Appalachians and Rockies. The
southern flying squirrel occurs in the central and
eastern United States (Fig. 5).
Fox squirrels and gray
squirrels inhabit the same kinds of forests, both
hardwood and coniferous, over much of their range. Gray
squirrels are more abundant where a high percentage of
land is forested. In areas with 10% forest cover, fox
and gray squirrel populations may be equal. Fox
squirrels prefer oak-hickory habitat over much of their
range, especially in the West. In Georgia and Florida,
fox squirrels seem to prefer pine timber. The western
gray squirrel prefers mixed hardwoods and conifers and
dry open hardwoods. Tassel-eared squirrels are strongly
associated with Ponderosa pine. Pine squirrels prefer
coniferous forests but also occur in mixed conifer and
hardwood forests, or sometimes in hardwood habitats.
Fox and gray squirrels
have similar food habits. They will eat a great variety
of native foods and adapt quickly to unusual food
sources. Typically, they feed on mast (wild tree fruits
and nuts) in fall and early winter. Acorns, hickory
nuts, walnuts, and osage orange fruits are favorite fall
foods. Nuts are often cached for later use. In late
winter and early spring they prefer tree buds. In summer
they eat fruits, berries, and succulent plant materials.
Fungi, corn, and cultivated fruits are taken when
available. During population peaks, when food is scarce,
these squirrels may chew bark from a variety of trees.
They will also eat insects and other animal matter.
Pine squirrels are often
heavily dependent on coniferous forests for cones and
buds but will also eat a variety of other foods common
to gray and fox squirrel diets. Douglas squirrels depend
largely on Ponderosa pine for food. Flying squirrels’
food habits are generally similar to those of other
squirrels. However, they are the most carnivorous of all
tree squirrels. They eat bird eggs and nestlings,
insects, and other animal matter when available. Flying
squirrels often occupy bird houses, especially bluebird
General Biology, Reproduction, and Behavior
Fox and gray squirrels
breed when they are 1 year old. They breed in
mid-December or early January and again in June. Young
squirrels may breed only once in their first year. The
gestation period is 42 to 45 days.
During the breeding
season, noisy mating chases take place when one or more
males pursue a female through the trees.
They nest in tree
cavities, human-made squirrel boxes, or in leaf nests.
Leaf nests are constructed with a frame of sticks filled
with dry leaves and lined with leaves, strips of bark,
corn husks, or other materials. Survival of young in
cavities is higher than in leaf nests. Cavities are the
preferred nest sites.
About 3 young comprise a
litter. At birth they are hairless, blind, and their
ears are closed. Newborns weigh about 1/2 ounce (14 g)
at birth and 3 to 4 ounces (84 to 112 g) at 5 weeks.
Young begin to explore outside the nest about the time
they are weaned at 10 to 12 weeks. At weaning they are
about half of their adult weight.
Home range size depends on
the season and availability of food. It may vary from 1
to 100 acres (0.4 to 40 ha). Squirrels move within their
range according to availability of food. They often seek
mast-bearing forests in fall and favor tender buds in
elm and maple forests in the spring.
During fall, squirrels may
travel 50 miles (80 km) or more in search of better
habitat. Squirrel populations periodically rise and
fall. During periods of high populations, squirrels—espe-cially
gray squirrels—may go on mass emigrations. At such times
many animals die.
Fox and gray squirrels are
vulnerable to numerous parasites and diseases. Ticks,
mange mites, fleas, and internal parasites are common.
Squirrel hunters often notice bot fly larvae (called
“wolves” or “warbles”) protruding from the skin. These
fly larvae do not impair the quality of the meat for
Squirrels are a food
source for hawks, owls, snakes, and several mammalian
predators. Predation seems to have little effect on
Typically about half the
squirrels in a population die each year. In the wild,
squirrels over 4 years old are rare, while in captivity
individuals may live 10 years or more.
The biology of other North
American squirrels has much in common with that of fox
and gray squirrels, although most other species have one
breeding season per year. Flying squirrels are unique in
that they are active at night. All other species are
active during the day.
Squirrels may occasionally
damage forest trees by chewing bark from branches and
trunks. Pine squirrels damage Ponderosa pine, jack pine,
and paper birch. In the Southeast, fox squirrels damage
loblolly and other pines.
These species and others
may eat cones and nip twigs to the extent that they
interfere with natural reseeding of important forest
trees. This is a particular problem in Ponderosa pine
forests where pine squirrels may remove 60% to 80% of
the cones in poor to fair seed years. In forest seed
orchards, such squirrel damage interferes with
commercial seed production.
In nut orchards, squirrels
can severely curtail production by eating nuts
prematurely and by carrying off mature nuts. In New
England fruit orchards, pine squirrels may eat ovaries
of cherry blossoms and destroy ripe pears. Pine, gray,
and fox squirrels may chew bark of various orchard
In residential areas,
squirrels sometimes travel powerlines and short out
transformers. They gnaw on wires, enter buildings, and
build nests in attics. They frequently chew holes
through pipelines used in maple syrup production.
damage lawns by burying or searching for and digging up
nuts. They will chew bark and clip twigs on ornamental
trees or shrubbery planted in yards. Often squirrels
take food at feeders intended for birds. Sometimes they
chew to enlarge openings of bird houses and then enter
to eat nestling songbirds. Flying squirrels are small
enough to enter most bird houses and are especially
likely to eat nesting birds.
In gardens, squirrels may
eat planted seeds, mature fruits, or grains such as
Fox and gray squirrels are
usually classified as game animals in states where they
occur. The tassel-eared squirrel is normally a protected
species. Check with local or state authorities to
determine legal status of squirrels in your area.
Damage Prevention and Control Methods
Prevent squirrels from
climbing isolated trees and power poles by encircling
them with a 2-foot-wide (61-cm) collar of metal 6 feet
(1.8 m) off the ground. Attach metal using encircling
wires held together with springs to allow for tree
Prevent squirrels from
traveling on wires by installing 2-foot (61-cm) sections
of lightweight 2- to 3-inch diameter (5.1- to 7.6-cm)
plastic pipe. Slit the pipe lengthwise, spread it open,
and place it over the wire. The pipe will rotate on the
wire and cause traveling squirrels to tumble.
Close openings to attics
and other parts of buildings but make sure not to lock
squirrels inside. They may cause a great deal of damage
in their efforts to chew out. Place traps inside as a
precaution after openings are closed. A squirrel
excluder can be improvised by mounting an 18-inch
(46-cm) section of 4-inch (10-cm) plastic pipe over an
opening. The pipe should point down at a 45o angle. A
one-way door can also be used over an opening to let
squirrels out and prevent them from returning.
Close openings to
buildings with heavy 1/2-inch (1.3-cm) wire mesh or make
other suitable repairs.
Custom-designed wire mesh
fences topped with electrified wires may effectively
keep out squirrels out of gardens or small orchards.
Trim limbs and trees to 6
to 8 feet (1.8 to 2.4 m) away from buildings to prevent
squirrels from jumping onto roofs.
In backyards where
squirrels are causing problems at bird feeders, consider
providing an alternative food source. Wire or nail an
ear of corn to a tree or wooden fence post away from
where the squirrels are causing problems.
In high-value crop
situations, it may pay to remove woods or other trees
near orchards to block the “squirrel highway.”
Naphthalene (moth balls)
may temporarily discourage squirrels from entering
attics and other enclosed spaces. Use of naphthalene in
attics of occupied buildings is not recommended,
however, because it can cause severe distress to people.
Supplement this method with lights. A cat in the attic
may discourage squirrels.
Ro-pel is a taste
repellent that can be applied to seeds, bulbs, and
flowers; trees and shrubs; poles and fences; siding and
outdoor furniture. Capsaicin is also a taste repellent,
registered for use on maple sap collecting equipment.
Polybutenes are sticky
materials that can be applied to buildings, railings,
downspouts, and other areas to keep squirrels from
climbing. They can be messy. A preapplication of masking
tape is recommended.
None are registered.
None are registered.
A variety of traps will
catch squirrels, including No. 0 or No. 1 leghold traps,
the “Better Squirrel and Rat Trap,” box traps, and cage
traps. Regular rat-sized snap traps will catch flying
squirrels and small pine squirrels. Glue traps for rats
will catch small squirrels.
Since squirrels are
classified as game species in most states, trapping
permits may be required from your local state wildlife
agency or municipal Animal Control office. Wire cage
traps and box traps can be used to capture squirrels
alive. Tie trap doors open for 2 to 3 days to get
squirrels accustomed to feeding in the traps. Then set
the traps and check them twice daily. Inform your
neighbors of your trapping activities. Translocation of
tree squirrels is a questionable practice because of the
stress placed on transported and resident squirrels and
concerns regarding the transmission of diseases.
Good baits are slices of
orange and apple, walnuts or pecans removed from the
shell, and peanut butter. Other foods familiar to the
squirrel may also work well, such as corn or sunflower
Where firearms are
permitted, shooting is effective. A shotgun with No. 6
shot or a .22-caliber rifle is suitable. Check with your
state wildlife agency for regulations pertaining to the
species in your area.
Often several control
methods used simultaneously are more successful than a
single method. For example, to remove a squirrel from an
attic, watch squirrels to determine where they enter.
Then use repellents and lights to drive them out. After
squirrels appear to have left the building, use
appropriate exclusion methods to keep them out. One or
more baited traps will catch squirrels that are
accidentally closed in. This last step is very important
because locked-in squirrels may cause damage when they
try to chew their way out.
Squirrel damage in yards,
gardens, forests, and orchards is often very difficult
to control. During population highs, new squirrels
arrive quickly to replace those shot or trapped.
Economics of Damage and Control
Squirrels cause economic
losses to homeowners, nut growers, and forest managers.
The extent of these losses is not well known.
Squirrels caused 177 power
outages in Lincoln, Nebraska, in 1980, which was 24% of
all outages. Estimated annual costs were $23,364 for
repairs, public relations, and lost revenue. In Omaha,
in 1985, squirrels caused 332 outages costing at least
$47,144. After squirrel guards were installed over
pole-mounted transformers in Lincoln in 1985, annual
costs were reduced 78% to $5,148.
References by Boggess
(1980) and Flyger and Gates (1982a,b) were particularly
useful in preparing this publication. The manuscript was
read and improved by the comments of Elizabeth McGhee.
Figure 1 from Schwartz and
Figures 2 through 4
adapted from Flyger and Gates (1982a,b) by Jill Sack
Figure 5 adapted from Burt
and Grossenheider (1976) by David Thornhill.
For Additional Information
Baumgartner, L. L. 1940.
Trapping, handling and marking fox squirrels. J. Wildl.
Boggess, E. K. 1980. Tree
squirrels. in F. R. Henderson, ed. Prevention and
control of wildlife damage. Great Plains Agric. Council
and Kansas Coop. Ext. Serv. Kansas State Univ.,
Burt, W. H., and R. P.
Grossenheider. 1976. A field guide to the mammals, 3d
ed. Houghton Mifflin Co. Boston. 289 pp.
Davison, V. E. 1964.
Selection of foods by gray squirrels. J. Wildl. Manage.
Dolan, P. G., and D. C.
Carter. 1977. Glaucomys volans. Mammal. Species 78:1-6.
Flyger, V., and J. E.
Gates. 1982 a. Fox and gray squirrels. Pages 209-229 in
J. A. Chapman and G. A. Feldhamer, eds. Wild mammals of
North America: biology, management, and economics. The
Johns Hopkins Univ. Press, Baltimore.
Flyger, V., and J. E.
Gates. 1982b. Pine squirrels. Pages 230-238 in J. A.
Chapman and G. A. Feldhamer, eds. Wild mammals of North
America: biology, management, and economics. The Johns
Hopkins Univ. Press, Baltimore.
Hall, R. E., and K. R.
Kelson. 1959. The mammals of North America, Vol. 1. The
Ronald Press Co., New York. 546 pp.
Hamilton, J. C., R. J.
Johnson, R. M. Case, and M. W. Riley. 1988. Assessment
of squirrel-caused power outages. Vertebr. Pest Control
Manage. Mater. 6:34-41.
Madson, J. 1964. Gray and
fox squirrels. Olin Mathieson Chem. Corp. East Alton,
Illinois. 112 pp.
Nash, D. J., and R. N.
Seaman. 1977. Sciurus aberti. Mammal. Species 80:1-5.
National Pest Control
Association. 1964. Tree squirrels—a fact sheet. Nat.
Pest Control Assoc. Tech. Release 20-64.
Schwartz, C. W., and E. R.
Schwartz. 1981. The wild mammals of Missouri, rev. ed.
Univ. Missouri Press, Columbia. 356 pp.
Scott E. Hygnstrom, Robert
M. Timm, Gary E. Larson
PREVENTION AND CONTROL OF
WILDLIFE DAMAGE — 1994
Division Institute of Agriculture and Natural Resources
University of Nebraska -Lincoln
United States Department
of Agriculture Animal and Plant Health Inspection
Service Animal Damage Control
Great Plains Agricultural
Council Wildlife Committee