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. Prebait- Grain baits may be more acceptable crops discourage ground squirrels ing means exposing squirrels to during the spring when the amount of somewhat. Squirrels, however, usually untreated grain bait several days green vegetation is limited. Pelletized adapt by building the major part of before using toxic grain. Conditioning baits using alfalfa or grass as a major their burrows at the margins of fields, the squirrels to eating this new food constituent may be preferred later in where they have access to the crop. improves the likelihood of their eating the season. During the early part of the season a lethal dose of toxic grain. Prebaiting It is important to test the acceptance of they begin foraging from the existing often improves bait acceptance and, a bait before a formal baiting program burrow system into the field until their therefore, control. The major disad- begins. Place clean (untreated) grains comfort escape zone is exceeded. vantage is the cost of labor and materi- by several active burrows. Use only When this zone is exceeded and as the als for prebaiting. grains acceptable to the animals as a litters mature in the colony, tunnels bait carrier. If none of the grains are will be extended into the feeding area. Zinc phosphide is classified as a consumed, the same procedure can be Late in the summer or fall, tillage will Restricted Use Pesticide and as such, repeated for pelletized baits. Several destroy these tunnels but will not dis- can only be purchased or used with formulations may need to be tried turb or destroy the original system at proper certification from the state. Cer- before an acceptable bait is selected. the edge of the field. tification information can be obtained

B-161 If control with one bait is unsuccessful, Most are only effective in tight, com- unsatisfactory or undesirable. Jaw rebaiting with another toxicant may pact, moist soils over 60o F (15o C). The traps (No. 1 or No. 0), box or cage produce the desired results. This is gas dissipates too rapidly in loose dry traps, and burrow entrance traps may particularly important when zinc soils to be effective in any extensive be used. phosphide is used. Follow-up treat- burrow system. Ground squirrel bur- Place leghold traps where squirrels ments with an anticoagulant will often row systems are often complex with will travel over them when entering control the remaining animals. several openings and numerous inter- and leaving their burrows. Conceal the connecting tunnels. The cost of using Bait placement is critical. Bait should trap by placing it in a shallow excava- gas cartridges may be more than eight be scattered adjacent to each active tion and covering it with 1/8 to 1/4 times the cost of using toxic baits. burrow in the amount and manner inch (0.3 to 0.6 cm) of soil. Be certain specified on the label. It should not be Fumigants registered for ground squir- that there is no soil beneath the trap placed in the burrow, because it will rel control include aluminum phos- pan to impede its action. No bait is either be covered with soil or pushed phide and gas cartridges. Cartridges necessary. out of the hole by the squirrels. may contain several combustible ingre- Box or cage traps may be set in any Ground squirrels are accustomed to dients. areas frequented by ground squirrels. foraging above ground for their food When using aluminum phosphide, Place them solidly on the ground so and are suspicious of anything placed place tablets at multiple entrances at that they will not tip or rock when the in their tunnel systems. All active bur- the same time. Insert the tablets as far squirrel enters. Never place the trap rows must be baited. Incomplete cov- back into the burrows as possible. directly over a hole or on a mound. erage of the colony will result in poor Water may be added to the soil to Cover the floor of the trap with soil control success. improve activity. Never allow alumi- and bait it with fresh fruit, vegetables, Where broadcast applications are not num phosphide to come into direct greens, peanut butter, or grain. Experi- allowed, baits can be placed in spill- contact with water, because the two ment to find the best bait or combina- proof containers. Old tires have been together can be explosive. Crumpled tion of baits for your area and time of extensively used in the past but are paper should be placed in the hole to year. Wire the door of the trap open bulky, heavy, and time-consuming to prevent the fumigant from being for 2 to 3 days and replenish the bait cut apart and move. Furthermore, bait pushed out of the hole by the animals daily to help overcome the squirrel’s can easily be pushed out by the ani- or being covered by loose soil. Plug the trap shyness and increase trapping mals and the tires can ruin a good burrow opening with soil to form an success. sickle bar or header if not removed air-tight seal. Monitor the area for Burrow entrance traps may also be from a field before harvest. Corru- escaping gas and plug holes as needed. useful. See Thirteen-lined Ground gated plastic drain pipe of different When using gas cartridges, punch five Squirrels for a description of this type diameters cut into 18- to 24-inch (46- to or six holes in one end of each gas car- of trap. 61-cm) lengths provide an inexpensive, tridge and loosen the contents for light-weight, and easy-to-use alterna- more complete combustion before use. Shooting tive. Insert and light a fuse. Gently slide the Shooting may provide relief from Bait stations should be placed in the cartridge, fuse end first, as far back ground squirrel depredation where field at about 50-foot (15-m) intervals a into the burrow opening as possible very small colonies are under constant week or so before treatments are to and immediately seal the hole with shooting pressure. It is, however, an begin. Once the animals use the sta- soil. Do not cover or smother the car- expensive and time-consuming prac- tions frequently, baiting can begin. Not tridge. Follow all label instructions. tice. Hunting licenses may be required all bait stations will be used by the Phosphine gas is toxic to all forms of in some states. squirrels at the same time or with the animal life. Inhalation can produce a same frequency. Each station should sensation of pressure in the chest, diz- Other Methods be checked every 24 hours and con- ziness, nausea, vomiting, and a rapid sumed or contaminated baits replaced Gas exploding devices for controlling onset of stupor. Affected people or ani- until feeding stops. When the desired burrowing rodents have not proven to mals should be exposed to fresh air level of control has been achieved, the be effective. Propane/oxygen mixtures and receive immediate medical atten- bait stations should be removed from injected for 45 seconds and then tion. Never carry a container of alumi- the field and the old bait returned to ignited only reduced the population by num phosphide in an enclosed vehicle. the original container or properly dis- about 40%. Vacuum devices that suck posed. rodents out of their burrows are Trapping currently being developed and tested. Fumigants No reliable data, however, exist at this Traps are best suited for removal of time to confirm or deny their efficacy. Fumigants are best suited to small small populations of ground squirrels acreages of light squirrel infestations. where other control methods are

B-162 Matschke, G. H., and K. A. Fagerstone. 1982. Economics of Damage For Additional Population reduction of Richardson’s and Control Information ground squirrels with zinc phosphide. J. Wildl. Manage. 46:671-677. Very little is known about the eco- Albert, S. W., and C.R. Record. 1982. Efficacy Matschke, G. H., M. P. Marsh, and D. L. Otis. and cost of four rodenticides for controlling 1983. Efficacy of zinc phosphide broadcast nomic consequences of ground squir- Columbian ground squirrel in western baiting for controlling Richardson’s ground rels foraging in agriculture. A single Montana. Great Plains Wildl. Damage squirrels on rangeland. J. Range. Manage. pair and their offspring can remove Control Workshop. 5:218-230. 36:504-506. about 1/4 acre (0.1 ha) of wheat or Andelt, W. F., and T. M. Race. 1991. Managing Pfeifer, S. 1980. Aerial predation of Wyoming alfalfa during one season. Water lost Wyoming (Richardson’s) ground squirrels in ground squirrels. J. Mamm. 61:371-372. Colorado. Coop. Ext. Bull. 6.505, Colorado from one canal can flood thousands of State Univ. 3 pp. Schmutz, J. K., and D. J. Hungle. 1989. acres or cause irrigation failures. The Populations of ferruginous and Swainson’s Askham, L. R. 1985. Effectiveness of two hawks increase in synchrony with ground crop loss and cost of repair can be very anticoagulant rodenticides (chlorophacinone squirrels. Can. J. Zool. 67:2596-2601. expensive. Prevention, by incorporat- and bromadiolone) for Columbian ground Schwartz, C. W., and E. R. Schwartz. 1981. The ing a rodent management plan into the squirrel (Spermophilus columbianus) control in eastern Washington. Crop Protect. 4(3):365- wild mammals of Missouri, rev. ed. Univ. total operation of an enterprise, far 371. Missouri Press, Columbia. 356 pp. outweighs the cost of added manage- Askham, L. R. 1990. Effect of artificial perches Sullins, M., and D. Sullivan. 1992. Observations ment practices. and nests in attracting raptors to orchards. of a gas exploding device for controlling Proc. Vertebr. Pest. Conf. 14:144-148. burrowing rodents. Proc. Vertebr. Pest Conf. 15:308-311. Acknowledgments Askham, L. R., and R. M. Poché. 1992. Biodeterioration of cholorphacinone in voles, Tomich, P. Q. 1992. Ground squirrels. Pages 192-208 in J. A. Chapman and G. A. Figure 1 from Schwartz and Schwartz (1981). hawks and an owl. Mammallia 56(1):145-150. Feldhamer. eds. Wild mammals of North Figures 2 and 3 adapted from Burt and Burt, W. H., and R. P. Grossenheider. 1976. A America. The Johns Hopkins Univ. Press., Grossenheider (1976) by David Thornhill. field guide to the mammals, 3d ed. Baltimore, Maryland. Houghton Mifflin Co., Boston. 289 pp. Some of the material included in this draft was Wobeser, G. A., and F. A. Weighton. 1979. A Edge, W. D., and S. L. Olson-Edge. 1990. A written by C. Ray Record in the 1983 edition of simple burrow entrance live trap for ground comparison of three traps for removal of squirrels. J. Wildl. Manage. 43:571-572. Prevention and Control of Wildlife Damage. 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. Editors Scott E. Hygnstrom Lewis, S. R., and J. M. O’Brien. 1990. Survey of Robert M. Timm rodent and rabbit damage to alfalfa hay in Gary E. Larson Nevada. Proc. Vertebr. Pest Conf. 14:116-119.

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