Leonard R. Askham Professor Emeritus FRANKLIN, Department of Horticulture and Landscape Architecture Washington State University RICHARDSON, Pullman, Washington 99164-6414 COLUMBIAN, WASHINGTON, AND TOWNSEND Fig. 1. Franklin ground squirrel, Spermophilus franklinii GROUND SQUIRRELS Damage Prevention and Repellents Fumigants Control Methods None are registered. Aluminum phosphide. Toxicants Exclusion Gas cartridge. Zinc phosphide. Limited usefulness. Trapping Chlorophacinone. Cultural Methods Box traps. Diphacinone. Flood irrigation, forage removal, crop Burrow-entrance traps. rotation, and summer fallow may Note: Not all toxicants are registered Leghold traps. reduce populations and limit for use in every state. Check regis- Shooting spread. tration labels for limitations within each state. Limited usefulness. PREVENTION AND CONTROL OF WILDLIFE DAMAGE — 1994 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 B-159 Great Plains Agricultural Council Wildlife Committee Identification deposition of fat necessary for hiberna- tion. Most store large quantities of The Franklin ground squirrel (Spermo- food in burrow caches. Some species, philus franklinii, Fig. 1) is a rather drab like the Franklin, eat a greater amount grayish brown. Black speckling gives a of animal matter, including ground- spotted or barred effect. Head and nesting bird eggs. Insects and other body average 10 inches (25.4 cm) with animal tissue may comprise up to one- a 5- to 6-inch (12.7- to 15.2-cm) tail. fourth of their diet. Adults weigh from 10 to 25 ounces (280 to 700 g). General Biology, The Richardson ground squirrel (S. richardson) is smaller and lighter Reproduction, and colored than the Franklin. Some are Behavior dappled on the back. The squirrel’s Fig. 2. Range of Franklin (dark) and Townsend body measures about 8 inches (20.3 ground squirrels (light) in North America. Ground squirrels construct and live in cm) with a tail of from 2 to 4 inches (5 extensive underground burrows, to 10 cm). Adults weigh from 11 to 18 sometimes up to 6 feet (2 m) deep, ounces (308 to 504 g). with many entrances. They also use and improve on the abandoned bur- The Columbian ground squirrel (S. rows of other mammals such as prairie columbianus) is easily distinguished dogs and pocket gophers. Most return from others in its range by its distinc- to their nests of dried vegetation tive coloration. Reddish brown within the burrows at night, during (rufous) fur is quite evident on the the warmest part of summer days, and nose, forelegs, and hindquarters. The when they are threatened by preda- head and body measure 10 to 12 tors, such as snakes, coyotes, foxes, inches (25.4 to 30.5 cm) in length with weasels, badgers, and raptors. a 3- to 5-inch (7.6- to 12.7-cm) tail. An average adult weighs more than 16 The squirrels generally enter their bur- ounces (454 g). rows to estivate, escaping the late sum- mer heat. They hibernate during the The Washington ground squirrel (S. coldest part of the winter. Males usu- washingtoni) has a small smoky-gray Fig. 3. Range of Richardson (light), Columbian (medium), and Washington ground squirrels ally become active above ground 1 to 2 flecked body with dappled whitish (dark) in North America. weeks before the females in the spring, spots. The tail is short with a blackish sometimes as early as late February or tip. This squirrel is similar to early March. A few may be active Townsend and Belding squirrels Range above ground throughout the year. except the latter have no spots. Head Breeding takes place immediately after and body are about 6 to 7 inches long Ground squirrels are common emergence. The young are born after a (15.2 to 18 cm); the tail 1.3 to 2.5 inches throughout the western two-thirds of 4- to 5-week gestation period with 2 to long (3.4 to 6.4 cm); and adults weigh 6 the North American continent. Most 10 young per litter. Generally only 1 to 10 ounces (168 to 280 g). are common to areas of open sage- litter is produced each year. Densities brush and grasslands and are often The Townsend ground squirrel’s (S. of the ground squirrel populations can found in and around dryland grain townsendi) head and body range in range from 2 to 20 or more per acre (5 fields, meadows, hay land, and irri- length from 5.5 to 7 inches (14 to 18 to 50/ha). gated pastures. Details of each species cm). It has a short bicolored tail about range, which overlap occasionally, are 1.3 to 2.3 inches (3 to 6 cm) long, and shown in figures 2 and 3. weighs approximately 6 to 9 ounces Damage and Damage (168 to 252 g). The body is smoky-gray Identification washed with a pinkish-buff. The belly Food Habits and flanks are whitish. High populations of ground squirrels Ground squirrels eat a wide variety of may pose a serious pest problem. The Other species not described here food. Most prefer succulent green veg- squirrels compete with livestock for because they cause few economic etation (grasses, forbs, and even brush) forage; destroy food crops, golf problems are Idaho (S. brunneus), when available, switching to dry courses, and lawns; and can be reser- Uinta (S. armatus), Mexican (S. mexi- foods, such as seeds, later in the year. voirs for diseases such as plague. Their canus), Spotted (S. spilosoma), Mohave The relatively high nutrient and oil burrow systems have been known to (S. mohavensis), and roundtail (S. content of the seeds aids in the weaken and collapse ditch banks and tereticaudus) ground squirrels. B-160 canals, undermine foundations, and Some research has been conducted on from your local Cooperative Extension alter irrigation systems. The mounds the effect of tall vegetation on ground or state department of agriculture of soil excavated from their burrows squirrel populations and movements. office. Zinc phosphide can be absorbed not only cover and kill vegetation, but The data, while sketchy, indicate that in small amounts through the skin. damage haying machinery. In addi- the squirrels may move out of tall veg- Rubber gloves should be worn when tion, some ground squirrels prey on etation stands to more open grass handling the bait. the eggs and young of ground-nesting fields. The addition of raptor (hawk, Use only fresh bait. Spoiled or con- birds or climb trees in the spring to owl, and kestrel) nest boxes and taminated baits will not be eaten by feed on new shoots and buds in perches around the field border or ground squirrels. Old bait may not be orchards. throughout the colony may reduce sufficiently toxic to be effective. If zinc colony growth, but is not a reliable phosphide baits are more than a few Legal Status damage control method. months old they should not be used, Ground squirrels generally are unpro- Toxicants particularly if they have not been stored in air-tight, sealed containers, tected. However, species associated Zinc phosphide and anticoagulants are with them, such as black-footed fer- because they decompose with humid- currently registered for ground squir- ity in the air. rets, weasels, wolves, eagles, and other rel control. Since pesticide registrations carnivores may be protected. Local vary from state to state, check with Chlorophacinone and diphacinone are laws as well as specific label restric- your local extension, USDA-APHIS- two anticoagulant baits that have been tions should be consulted before initi- Animal Damage Control, or state registered in some states for ground ating lethal control measures. department of agriculture for use limi- squirrel control and have been found tations. Additional restrictions may be to be quite effective. Both are formu- Damage Prevention and in effect for areas where endangered lated under a number of trade names. Control Methods species have been identified. Death will occur within 4 to 9 days if a continual supply of the bait is con- Exclusion Zinc phosphide has been used for sev- sumed. If baiting is interrupted or a eral years to control ground squirrels. sufficient amount is not maintained Exclusion is impractical in most cases It is a single-dose toxicant which, during the control period, the toxic because ground squirrels are able to when used properly, can result in mor- effects of the chemicals wear off and dig under or climb over most simple tality rates as high as 85% to 90%. If, the animal will recover. barriers. Structures truly able to however, the targeted animals do not exclude them are prohibitively expen- consume enough bait for mortality to Baiting should not begin until the sive for most situations. Sheet metal occur, they become sick, associate their entire population is active, 2 to 3 collars are sometimes used around tree illness with the food source they have weeks after the first adults appear. If a trunks to prevent damage to the base just consumed, and are reluctant to re- portion of the population is in hiberna- of the trees or to keep animals from turn to the bait. This is called “bait shy- tion or estivation, only the active ani- climbing trees to eat fruit or nut crops. ness.” Repeated baiting with the same mals will be affected. bait formulations is generally unsuc- Bait selection should be based on the Cultural Methods/Habitat cessful, particularly when tried during animal’s feeding habits, time of year, Modification the same year. and crop type. Ground squirrel feed- Flood irrigation of hay and pasture Prebaiting may increase bait accep- ing habits vary with the time of year. lands and frequent tillage of other tance with treated grain baits.