RODENTS: Squirrels, Franklin, Richardson,
Columbian Washington and Townsend
Franklin ground squirrel, Spermophilus franklinii
Prevention and Control Methods
Flood irrigation, forage removal, crop rotation, and
summer fallow may reduce populations and limit
None are registered.
Note: Not all toxicants are registered for use in
every state. Check registration labels for
limitations within each state.
Aluminum phosphide. Gas cartridge.
Box traps. Burrow-entrance traps. Leghold traps.
The Franklin ground
squirrel (Spermophilus franklinii, Fig. 1) is a rather
drab grayish brown. Black speckling gives a spotted or
barred effect. Head and body average 10 inches (25.4 cm)
with a 5- to 6-inch (12.7- to 15.2-cm) tail. Adults
weigh from 10 to 25 ounces (280 to 700 g).
The Richardson ground
squirrel (S. richardson) is smaller and lighter colored
than the Franklin. Some are dappled on the back. The
squirrel’s body measures about 8 inches (20.3 cm) with a
tail of from 2 to 4 inches (5 to 10 cm). Adults weigh
from 11 to 18 ounces (308 to 504 g).
The Columbian ground
squirrel (S. columbianus) is easily distinguished from
others in its range by its distinctive coloration.
Reddish brown (rufous) fur is quite evident on the nose,
forelegs, and hindquarters. The head and body measure 10
to 12 inches (25.4 to 30.5 cm) in length with a 3- to
5-inch (7.6-to 12.7-cm) tail. An average adult weighs
more than 16 ounces (454 g).
The Washington ground
squirrel (S. washingtoni) has a small smoky-gray flecked
body with dappled whitish spots. The tail is short with
a blackish tip. This squirrel is similar to Townsend and
Belding squirrels except the latter have no spots. Head
and body are about 6 to 7 inches long (15.2 to 18 cm);
the tail 1.3 to 2.5 inches long (3.4 to 6.4 cm); and
adults weigh 6 to 10 ounces (168 to 280 g).
The Townsend ground
squirrel’s (S. townsendi) head and body range in length
from 5.5 to 7 inches (14 to 18 cm). It has a short
bicolored tail about 1.3 to 2.3 inches (3 to 6 cm) long,
and weighs approximately 6 to 9 ounces (168 to 252 g).
The body is smoky-gray washed with a pinkish-buff. The
belly and flanks are whitish.
Other species not
described here because they cause few economic problems
are Idaho (S. brunneus), Uinta (S. armatus), Mexican (S.
mexicanus), Spotted (S. spilosoma), Mohave (S.
mohavensis), and roundtail (S. tereticaudus) ground
Ground squirrels are
common throughout the western two-thirds of the North
American continent. Most are common to areas of open
sagebrush and grasslands and are often found in and
around dryland grain fields, meadows, hay land, and
irrigated pastures. Details of each species range, which
overlap occasionally, are shown in figures 2 and 3.
Ground squirrels eat a
wide variety of food. Most prefer succulent green
vegetation (grasses, forbs, and even brush) when
available, switching to dry foods, such as seeds, later
in the year. The relatively high nutrient and oil
content of the seeds aids in the deposition of fat
necessary for hibernation. Most store large quantities
of food in burrow caches. Some species, like the
Franklin, eat a greater amount of animal matter,
including ground-nesting bird eggs. Insects and other
animal tissue may comprise up to one-fourth of their
General Biology, Reproduction, and Behavior
Ground squirrels construct
and live in extensive underground burrows, sometimes up
to 6 feet (2 m) deep, with many entrances. They also use
and improve on the abandoned burrows of other mammals
such as prairie dogs and pocket gophers. Most return to
their nests of dried vegetation within the burrows at
night, during the warmest part of summer days, and when
they are threatened by predators, such as snakes,
coyotes, foxes, weasels, badgers, and raptors.
The squirrels generally
enter their burrows to estivate, escaping the late
summer heat. They hibernate during the coldest part of
the winter. Males usually become active above ground 1
to 2 weeks before the females in the spring, sometimes
as early as late February or early March. A few may be
active above ground throughout the year. Breeding takes
place immediately after emergence. The young are born
after a 4-to 5-week gestation period with 2 to 10 young
per litter. Generally only 1 litter is produced each
year. Densities of the ground squirrel populations can
range from 2 to 20 or more per acre (5 to 50/ha).
Damage and Damage Identification
High populations of ground
squirrels may pose a serious pest problem. The squirrels
compete with livestock for forage; destroy food crops,
golf courses, and lawns; and can be reservoirs for
diseases such as plague. Their burrow systems have been
known to weaken and collapse ditch banks and canals,
undermine foundations, and alter irrigation systems. The
mounds of soil excavated from their burrows not only
cover and kill vegetation, but damage haying machinery.
In addition, some ground squirrels prey on the eggs and
young of ground-nesting birds or climb trees in the
spring to feed on new shoots and buds in orchards.
Ground squirrels generally
are unprotected. However, species associated with them,
such as black-footed ferrets, weasels, wolves, eagles,
and other carnivores may be protected. Local laws as
well as specific label restrictions should be consulted
before initiating lethal control measures.
Prevention and Control Methods
Exclusion is impractical
in most cases because ground squirrels are able to dig
under or climb over most simple barriers. Structures
truly able to exclude them are prohibitively expensive
for most situations. Sheet metal collars are sometimes
used around tree trunks to prevent damage to the base of
the trees or to keep animals from climbing trees to eat
fruit or nut crops.
Flood irrigation of hay
and pasture lands and frequent tillage of other crops
discourage ground squirrels somewhat. Squirrels,
however, usually adapt by building the major part of
their burrows at the margins of fields, where they have
access to the crop. During the early part of the season
they begin foraging from the existing burrow system into
the field until their comfort escape zone is exceeded.
When this zone is exceeded and as the litters mature in
the colony, tunnels will be extended into the feeding
area. Late in the summer or fall, tillage will destroy
these tunnels but will not disturb or destroy the
original system at the edge of the field.
Some research has been
conducted on the effect of tall vegetation on ground
squirrel populations and movements. The data, while
sketchy, indicate that the squirrels may move out of
tall vegetation stands to more open grass fields. The
addition of raptor (hawk, owl, and kestrel) nest boxes
and perches around the field border or throughout the
colony may reduce colony growth, but is not a reliable
damage control method.
Zinc phosphide and
anticoagulants are currently registered for ground
squirrel control. Since pesticide registrations vary
from state to state, check with your local extension,
USDA-APHIS-Animal Damage Control, or state department of
agriculture for use limitations. Additional restrictions
may be in effect for areas where endangered species have
Zinc phosphide has been
used for several years to control ground squirrels. It
is a single-dose toxicant which, when used properly, can
result in mortality rates as high as 85% to 90%. If,
however, the targeted animals do not consume enough bait
for mortality to occur, they become sick, associate
their illness with the food source they have just
consumed, and are reluctant to return to the bait. This
is called “bait shyness.” Repeated baiting with the same
bait formulations is generally unsuccessful,
particularly when tried during the same year.
Prebaiting may increase
bait acceptance with treated grain baits. Prebaiting
means exposing squirrels to untreated grain bait several
days before using toxic grain. Conditioning the
squirrels to eating this new food improves the
likelihood of their eating a lethal dose of toxic grain.
Prebaiting often improves bait acceptance and,
therefore, control. The major disadvantage is the cost
of labor and materials for prebaiting.
Zinc phosphide is
classified as a Restricted Use Pesticide and as such,
can only be purchased or used with proper certification
from the state. Certification information can be
obtained from your local Cooperative Extension or state
department of agriculture office. Zinc phosphide can be
absorbed in small amounts through the skin. Rubber
gloves should be worn when handling the bait.
Use only fresh bait.
Spoiled or contaminated baits will not be eaten by
ground squirrels. Old bait may not be sufficiently toxic
to be effective. If zinc phosphide baits are more than a
few months old they should not be used, particularly if
they have not been stored in air-tight, sealed
containers, because they decompose with humidity in the
diphacinone are two anticoagulant baits that have been
registered in some states for ground squirrel control
and have been found to be quite effective. Both are
formulated under a number of trade names. Death will
occur within 4 to 9 days if a continual supply of the
bait is consumed. If baiting is interrupted or a
sufficient amount is not maintained during the control
period, the toxic effects of the chemicals wear off and
the animal will recover.
Baiting should not begin
until the entire population is active, 2 to 3 weeks
after the first adults appear. If a portion of the
population is in hibernation or estivation, only the
active animals will be affected.
Bait selection should be
based on the animal’s feeding habits, time of year, and
crop type. Ground squirrel feeding habits vary with the
time of year. Grain baits may be more acceptable during
the spring when the amount of green vegetation is
limited. Pelletized baits using alfalfa or grass as a
major constituent may be preferred later in the season.
It is important to test
the acceptance of a bait before a formal baiting program
begins. Place clean (untreated) grains by several active
burrows. Use only grains acceptable to the animals as a
bait carrier. If none of the grains are consumed, the
same procedure can be repeated for pelletized baits.
Several formulations may need to be tried before an
acceptable bait is selected.
If control with one bait
is unsuccessful, rebaiting with another toxicant may
produce the desired results. This is particularly
important when zinc phosphide is used. Follow-up
treatments with an anticoagulant will often control the
Bait placement is
critical. Bait should be scattered adjacent to each
active burrow in the amount and manner specified on the
label. It should not be placed in the burrow, because it
will either be covered with soil or pushed out of the
hole by the squirrels. Ground squirrels are accustomed
to foraging above ground for their food and are
suspicious of anything placed in their tunnel systems.
All active burrows must be baited. Incomplete coverage
of the colony will result in poor control success.
applications are not allowed, baits can be placed in
spill-proof containers. Old tires have been extensively
used in the past but are bulky, heavy, and
time-consuming to cut apart and move. Furthermore, bait
can easily be pushed out by the animals and the tires
can ruin a good sickle bar or header if not removed from
a field before harvest. Corrugated plastic drain pipe of
different diameters cut into 18- to 24-inch (46-to
61-cm) lengths provide an inexpensive, light-weight, and
Bait stations should be
placed in the field at about 50-foot (15-m) intervals a
week or so before treatments are to begin. Once the
animals use the stations frequently, baiting can begin.
Not all bait stations will be used by the squirrels at
the same time or with the same frequency. Each station
should be checked every 24 hours and consumed or
contaminated baits replaced until feeding stops. When
the desired level of control has been achieved, the bait
stations should be removed from the field and the old
bait returned to the original container or properly
Fumigants are best suited
to small acreages of light squirrel infestations.
Most are only effective in
tight, compact, moist soils over 60o F (15o C). The gas
dissipates too rapidly in loose dry soils to be
effective in any extensive burrow system. Ground
squirrel burrow systems are often complex with several
openings and numerous interconnecting tunnels. The cost
of using gas cartridges may be more than eight times the
cost of using toxic baits.
Fumigants registered for
ground squirrel control include aluminum phosphide and
gas cartridges. Cartridges may contain several
When using aluminum
phosphide, place tablets at multiple entrances at the
same time. Insert the tablets as far back into the
burrows as possible. Water may be added to the soil to
improve activity. Never allow aluminum phosphide to come
into direct contact with water, because the two together
can be explosive. Crumpled paper should be placed in the
hole to prevent the fumigant from being pushed out of
the hole by the animals or being covered by loose soil.
Plug the burrow opening with soil to form an air-tight
seal. Monitor the area for escaping gas and plug holes
When using gas cartridges,
punch five or six holes in one end of each gas cartridge
and loosen the contents for more complete combustion
before use. Insert and light a fuse. Gently slide the
cartridge, fuse end first, as far back into the burrow
opening as possible and immediately seal the hole with
soil. Do not cover or smother the cartridge. Follow all
Phosphine gas is toxic to
all forms of animal life. Inhalation can produce a
sensation of pressure in the chest, dizziness, nausea,
vomiting, and a rapid onset of stupor. Affected people
or animals should be exposed to fresh air and receive
immediate medical attention. Never carry a container of
aluminum phosphide in an enclosed vehicle.
Traps are best suited for
removal of small populations of ground squirrels where
other control methods are unsatisfactory or undesirable.
Jaw traps (No. 1 or No. 0), box or cage traps, and
burrow entrance traps may be used.
Place leghold traps where
squirrels will travel over them when entering and
leaving their burrows. Conceal the trap by placing it in
a shallow excavation and covering it with 1/8 to 1/4
inch (0.3 to 0.6 cm) of soil. Be certain that there is
no soil beneath the trap pan to impede its action. No
bait is necessary.
Box or cage traps may be
set in any areas frequented by ground squirrels. Place
them solidly on the ground so that they will not tip or
rock when the squirrel enters. Never place the trap
directly over a hole or on a mound. Cover the floor of
the trap with soil and bait it with fresh fruit,
vegetables, greens, peanut butter, or grain. Experiment
to find the best bait or combination of baits for your
area and time of year. Wire the door of the trap open
for 2 to 3 days and replenish the bait daily to help
overcome the squirrel’s trap shyness and increase
Shooting may provide
relief from ground squirrel depredation where very small
colonies are under constant shooting pressure. It is,
however, an expensive and time-consuming practice.
Hunting licenses may be required in some states.
Gas exploding devices for
controlling burrowing rodents have not proven to be
effective. Propane/oxygen mixtures injected for 45
seconds and then ignited only reduced the population by
about 40%. Vacuum devices that suck rodents out of their
burrows are currently being developed and tested. No
reliable data, however, exist at this time to confirm or
deny their efficacy.
Economics of Damage and Control
Very little is known about
the economic consequences of ground squirrels foraging
in agriculture. A single pair and their offspring can
remove about 1/4 acre (0.1 ha) of wheat or alfalfa
during one season. Water lost from one canal can flood
thousands of acres or cause irrigation failures. The
crop loss and cost of repair can be very expensive.
Prevention, by incorporating a rodent management plan
into the total operation of an enterprise, far outweighs
the cost of added management practices.
Figure 1 from Schwartz and
Figures 2 and 3 adapted
from Burt and Grossenheider (1976) by David Thornhill.
Some of the material
included in this draft was written by C. Ray Record in
the 1983 edition of
Prevention and Control of
For Additional Information
Albert, S. W., and C.R. Record. 1982. Efficacy and cost
of four rodenticides for controlling Columbian ground
squirrel in western Montana. Great Plains Wildl. Damage
Control Workshop. 5:218-230.
Andelt, W. F., and T. M.
Race. 1991. Managing Wyoming (Richardson’s) ground
squirrels in Colorado. Coop. Ext. Bull. 6.505, Colorado
State Univ. 3 pp.
Askham, L. R. 1985.
Effectiveness of two anticoagulant rodenticides (chlorophacinone
and bromadiolone) for Columbian ground squirrel (Spermophilus
columbianus) control in eastern Washington. Crop
Askham, L. R. 1990. Effect
of artificial perches and nests in attracting raptors to
orchards. Proc. Vertebr. Pest. Conf. 14:144-148.
Askham, L. R., and R. M.
Poché. 1992. Biodeterioration of cholorphacinone in
voles, hawks and an owl. Mammallia 56(1):145-150.
Burt, W. H., and R. P.
Grossenheider. 1976. A field guide to the mammals, 3d
ed. Houghton Mifflin Co., Boston. 289 pp.
Edge, W. D., and S. L.
Olson-Edge. 1990. A comparison of three traps for
removal of Columbian ground squirrels. Proc. Vertebr.
Pest Conf. 14:104-106.
Fagerstone, K. A. 1988.
The annual cycle of Wyoming ground squirrels in
Colorado. J. Mamm. 69:678-687.
Lewis, S. R., and J. M.
O’Brien. 1990. Survey of rodent and rabbit damage to
alfalfa hay in Nevada. Proc. Vertebr. Pest Conf.
Matschke, G. H., and K. A.
Fagerstone. 1982. Population reduction of Richardson’s
ground squirrels with zinc phosphide. J. Wildl. Manage.
Matschke, G. H., M. P.
Marsh, and D. L. Otis. 1983. Efficacy of zinc phosphide
broadcast baiting for controlling Richardson’s ground
squirrels on rangeland. J. Range. Manage. 36:504-506.
Pfeifer, S. 1980. Aerial
predation of Wyoming ground squirrels. J. Mamm.
Schmutz, J. K., and D. J.
Hungle. 1989. Populations of ferruginous and Swainson’s
hawks increase in synchrony with ground squirrels. Can.
J. Zool. 67:2596-2601.
Schwartz, C. W., and E. R.
Schwartz. 1981. The wild mammals of Missouri, rev. ed.
Univ. Missouri Press, Columbia. 356 pp.
Sullins, M., and D.
Sullivan. 1992. Observations of a gas exploding device
for controlling burrowing rodents. Proc. Vertebr. Pest
Tomich, P. Q. 1992. Ground
squirrels. Pages 192-208 in J. A. Chapman and G. A.
Feldhamer. eds. Wild mammals of North America. The Johns
Hopkins Univ. Press., Baltimore, Maryland.
Wobeser, G. A., and F. A.
Weighton. 1979. A simple burrow entrance live trap for
ground squirrels. J. Wildl. Manage. 43:571-572.
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