Ground Squirrels
Twenty-three species and 119 subspecies of ground squirrels exist in the United States (Hall 1981).
Belding's, California and Rock Ground Squirrels
Identification
The Belding ground squirrel is medium-sized with a stocky build and short, furry (but not bushy) tail. It is brownish gray to reddish brown in color, and has no stripes, mottling or markings of any type. The underside of the body is dull cream-buff, paling on the throat and inner sides of the legs. Coloration varies somewhat with subspecies. The body is about 8 1/2 inches (21.6 cm) long, with a 2 1/2-inch (6.4-cm) tail. The ears are small and not prominent.
The California ground squirrel is 10 inches (25.4 cm) long and slightly larger than the Belding ground squirrel. It has a moderately long (6 1/2-inch [16.5-cm]) semi-bushy tail. Ears are tall and conspicuous, with some exceptionally long hairs at the tips. The fur is brownish gray and dusky, with a flecked or mottled and grizzly appearance. Fur markings vary with subspecies.
The rock ground squirrel is a large-sized, heavy-bodied, ground squirrel (10 1/2 inches [26.7 cm] long) with a moderately long (8-inches [20.3-cm]) bushy tail. Large prominent ears extend above the top of the head. The fur is grayish, brownish gray, or blackish and is mottled with light gray or whitish specks or spots; coloration varies with subspecies. This ground squirrel resembles the California ground squirrel in many ways, but is somewhat larger and has a longer and bushier tail. The ranges of the rock and the California ground squirrels do not overlap; hence the two squirrels cannot be confused with one another.
Range and Habitat
The Belding occupies the northeastern part of California, extending northward into eastern Oregon and eastward into the southwestern portion of Idaho. It also ranges into the north-central portion of Nevada. It is the most numerous and troublesome squirrel in Oregon and northeastern California.
The California ground squirrel's range extends along the far west coast from northern Mexico northward throughout much of California, the western half of Oregon, and a moderate distance into south-central Washington. This species is absent from the desert regions of California. It is the most serious native rodent pest in California, especially the subspecies S. b. fisheri and S. b. beecheyi, which occupy the Central Valley and the coastal region south from San Francisco.
The rock squirrel's range covers nearly all of Arizona and New Mexico. It extends eastward into southwestern Texas and northward into southern Nevada, and covers approximately two-thirds of Utah and Colorado. More than half of its range extends south into Mexico.
The large ranges of these three species cut across highly varied habitat. The habitat discussed here is more or less typical and the one most often associated with economic losses.
Belding ground squirrels live mainly in natural meadows and grasslands but are adaptive to alfalfa, irrigated pastures and the margins of grain fields. They may occupy meadows in forested areas at higher elevatins, but they avoid forests or dense brushlands.
California ground squirrels occupy grasslands and savannah-like areas with mixtures of oaks and grasslands. They avoid moderate to heavily forested areas or dense brushlands. They generally prefer open space, but they are highly adaptable to disturbed environments and will infest earthen dams, levees, irrigation ditch banks, railroad rights-of-way, and road embankments, and will readily burrow beneath buildings in rural areas. They thrive along the margins of grain fields and other crops, feeding out into the field.
Rock squirrels inhabit rocky areas, hence their name. They live in rocky canyons or on rocky hillsides in arid environments, but they adapt to disturbed environments and will live along stone walls and roadside irrigation ditches, feeding out into cultivated fields.
Fun Facts & Trivia
All species of ground squirrels dig burrows for shelter and safety. The burrow systems are occupied year after year and are extended in length and complexity each year. Each system has numerous entrances which are always left open and never plugged with soil. The California and rock ground squirrels are more colonial in their habits. A number of squirrels occupy the same burrow system. The Belding ground squirrel is somewhat less colonial and its burrows are more widely dispersed.
Ground squirrels are rapid runners and good climbers. Of the three species, the California and rock ground squirrels are the most prone to climbing. When scared by humans or predators, ground squirrels always retreat to their burrows.
Ground squirrels are hibernators. Most or all of the adult population goes into hibernation during the coldest period of the year. Squirrels born the previous spring may not go into complete hibernation during the first winter. In hot arid regions they may estivate, which is a temporary summer sleep that may last for a few days to a couple of weeks.
Male California and Belding squirrels generally emerge from hibernation 10 to 14 days prior to the females. The reverse is reported for rock squirrels. Gestation is 28 to 32 days, and the young are born in a nest chamber in the burrow system. The young are born hairless with their eyes closed. They are nursed in the burrow until about 6 to 7 weeks of age (about one-third adult size), when they begin to venture above ground and start feeding on green vegetation. Only 1 litter is produced annually.
The litter size of the California ground squirrel averages slightly over 7, while that of the rock and Belding squirrels average 5 and 8, respectively. The rodent's relatively slow annual reproductive rate is compensated by a relatively long life span of 4 to 5 years.
Damage Identification
Two of the three species included in this chapter, the California and the Belding, are considered serious agricultural pests where they are found in moderate to high densities adjacent to susceptible crops or home gardens. Rock squirrels overall are relatively insignificant as agricultural pests even though their damage may be economically significant to individual growers. They are all adaptive and feed on a variety of crops, depending on the ones grown in proximity to their natural habitat. Since ground squirrels are active during daylight hours, and their burrow openings are readily discernible, damage identification is generally uncomplicated.
Their burrowing activities weaken levees, ditch banks, and earthen dams, and undermine roadways and buildings. Burrows can also result in loss of irrigation water by unwanted diversions, and in natural habitats they may cause accelerated soil erosion by channeling rain or snow runoff.
Burrow entrances in school playgrounds, parks and other recreational areas are responsible for debilitating falls, occasionally resulting in sprained or broken ankles or limbs. Burrows in horse exercising or jumping arenas or on equestrian trails can cause serious injuries to horses and to their riders if thrown.
The Belding ground squirrel, under favorable conditions, reaches incredible densities, often exceeding 100 per acre (247/ha). Extensive losses may be experienced in range forage, irrigated pastures, alfalfa, wheat, oats, barley, and rye.
The California ground squirrel, where numerous, significantly depletes the forage for livestock, reducing carrying capacity on rangeland as well as irrigated pasture land. All grains, and a wide variety of other crops, are consumed in agricultural regions by this opportunistic feeder.
Rock ground squirrels consume peas, squash, corn, and grains of all kinds. They also feed on various fruit and sometimes dig up and consume planted seed. Rock squirrels are not major pests, however, because their preferred natural habitat infrequently adjoins cultivated crops.
Public Health
All three are implicated in the transmission of certain diseases to people, notably plague.
Legal Status
The three species of ground squirrels discussed in this chapter are generally regarded as pests and, as such, are not protected. Local laws or regulations should, however, be consulted before undertaking lethal control.
Be aware that several of the numerous ground squirrel species are on the threatened or endangered species lists. Any control of pest species must take into consideration the safeguarding and protection of endangered ground squirrels and other rodent species.
Damage Prevention and Control Methods
Exclusion
Limited usefulness and costly.
Habitat Modification
Flood irrigation and deep tillage may help discourage ground squirrels. Eliminate brush, rock piles, and old unused farm machinery that serve as harborage for the California ground squirrel.
Repellents
None are very effective.
Toxicants
Zinc phosphide. Anticoagulants ( diphacinone and chlorophacinone ). Cholecalciferol (state registration only for rock squirrels).
Fumigants
Aluminum phosphide. Gas cartridges.
Franklin, Richardson, Columbian, Washington, and Townsend Ground Squirrels
Identification
The Franklin ground squirrel (Spermophilus franklinii) is a 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. It has reddish brown ( rufous ) fur 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. townsendi) is smoky-gray washed with a pinkish-buff and the belly and flanks are whitish. The head and body range in length from 5.5 to 7 inches (14 to 18 cm) and 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).
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 squirrels.
Range and Habitat
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. The ranges of some species overlap occasionally.
Fun Facts
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. 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.
The squirrels generally enter their burrows to estivate, escaping the late summer heat. They hibernate during the coldest part of the winter.
Densities of the ground squirrel populations can range from 2 to 20 or more per acre (5 to 50/ha).
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. 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.
Legal Status
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.
Damage Prevention and Control Methods
Exclusion
Limited usefulness.
Habitat Modification
Flood irrigation, forage removal, crop rotation, and summer fallow may reduce populations and limit spread.
Repellents
None are registered.
Toxicants
Zinc phosphide. Chlorophacinone. Diphacinone. Note: Not all toxicants are registered for use in every state. Check registration labels for limitations within each state.
Fumigants
Aluminum phosphide. Gas cartridge.
Trapping
Box traps. Burrow-entrance traps. Leghold traps.
ACKNOWLEDGEMENTS
The above information was adapted from PREVENTION AND CONTROL OF WILDLIFE DAMAGE with permission of the editors, Scott E. Hygnstrom, Robert M. Timm, and Gary E. Larson (Cooperative Extension 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).
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