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Home , Ground squirrel

CALIFORNIA GROUND

Integrated Pest Management for Home Gardeners and Landscape Professionals

The California , Sper- The burrows may be 5 to 30 feet or mophilus beecheyi (Fig. 1), is one of the more in length and may go 2 to 4 feet most troublesome pests to homeown- below the soil surface. Often there is ers and gardeners. It is found in nearly more than one opening in a burrow all regions of California except for the system. Ground live in colo- Owens Valley southward into the nies that may include several dozen desert regions. in a complex of burrows. More than one squirrel may live in a burrow. IDENTIFICATION Ground squirrels are easily identified Ground squirrels are active during the as they forage aboveground near their day, mainly from mid-morning burrows. The ground squirrel’s body through late afternoon, especially on measures 9 to 11 inches and its semi- warm, sunny days. Ground squirrels bushy tail adds another 5 to 9 inches in have two periods of dormancy during length. The fur is brownish gray and the year. During winter months most speckled with off-white along the back; ground squirrels hibernate, but some the sides of the head and shoulders are young may be active at this time, espe- light gray to whitish. One subspecies cially in areas where winters are not that occupies most of northern Califor- severe. During the hottest times of the nia has a dark, triangular-shaped patch year most adults go into a period of Figure 1. California ground squirrels. on its back between the shoulders; this inactivity, called estivation, that may patch is missing from other species. last a few days to a week or more. Dur- While ground squirrels are similar in ing these periods, the burrow appears tion, they feed almost exclusively on appearance to tree squirrels and may open at the entrance but the squirrel green grasses and herbaceous plants. climb trees, when frightened they will plugs it with soil near the . When annual plants begin to dry and always retreat to a burrow, whereas produce seed, squirrels switch to tree squirrels will climb a tree or tall Ground squirrels breed once a year, seeds, grains, and nuts, and begin to structure and never use a burrow. averaging seven to eight per litter. store food. Ground squirrels usually Timing of breeding varies with loca- forage close to their burrows. Their BIOLOGY AND BEHAVIOR tion: in southern California breeding home range typically is within a 75- Ground squirrels live in a wide variety begins in December, in the Central yard radius of their burrow. of natural but usually avoid Valley in February through April, and thick chaparral, dense woods, and wet somewhat later in the mountain DAMAGE areas. Populations may be particularly ranges. Aboveground activity by Ground squirrels damage many food- high in grazed rangelands and in areas adults is at a maximum at the height of bearing and ornamental plants. Par- disturbed by humans such as road or the breeding season. The young are ticularly vulnerable are grains and nut ditchbanks, fence rows, around build- born in the burrow and grow rapidly; and fruit trees such as almond, apple, ings, and in or bordering many crops. by about 6 weeks of age they usually apricot, orange, peach, pistachio, emerge from the burrow. At 6 months prune, and walnut. Ground squirrels Ground squirrels live in a burrow sys- of age they resemble adults. will enter gardens and devour veg- tem where they sleep, rest, rear young, etables in the seedling stage. They may store food, and avoid danger. The bur- Ground squirrels are primarily herb- damage young shrubs, vines, and trees row openings are about 4 inches in ivorous. Their diet changes with the by gnawing bark, girdling trunks, eat- diameter, but can vary considerably. season. After emergence from hiberna- ing twigs and leaves, and burrowing

PEST NOTES Publication 7438 University of California Agriculture and Natural Resources Revised January 2002 January 2002 California Ground Squirrel

around roots. Ground squirrels will erty may be controlled in any legal gnaw on plastic sprinkler heads and manner by the owner or tenant; tree irrigation lines. They also eat the eggs squirrels, on the other hand, are classi- of ground-nesting birds and may limit fied as game animals and have a hunt- attempts to attract quail to the yard. ing season.

Burrowing can be quite destructive. Note that the Burrows and mounds make it difficult (S. mohavensis) and the San Joaquin to mow, and they present hazards to (Ammospermophilus machinery, pedestrians, and livestock. nelsoni) are classified as threatened by Burrows around trees and shrubs can the U.S. Fish and Wildlife Service and damage and desiccate roots, and some- are protected. Although neither of times topple trees. Burrows beneath these relatively small squirrels is likely buildings and other structures some- to be misidentified as the much larger Figure 3. Box trap. times necessitate repair. California ground squirrel, their ranges could overlap in some areas. The en- Ground squirrels can harbor diseases dangered San Joaquin kit fox (Vulpes “References”), contact your county harmful to humans, particularly when macrotis mutica), several endangered agricultural commissioner for addi- squirrel populations are dense. A major species of kangaroo rats, the riparian tional information. concern is bubonic plague transmitted brush rabbit (Sylvilagus bachmani to humans by fleas carried on the squir- riparius), riparian wood rat (Neotoma MANAGEMENT rels. Ground squirrels are susceptible to fuscipes riparia), as well as some endan- The selection of control procedures is plague, which has wiped out entire gered amphibians and reptiles, are also heavily influenced by the unique life colonies. If you find unusual numbers found within California ground squir- cycle and behavior of the ground of squirrels or other dead for rels’ range and could be impacted by squirrel. For example, baiting with no apparent reason, notify public some squirrel control techniques. Be- treated grain is effective in summer health officials. Do not handle dead fore using pesticides for ground squir- and fall because squirrels primarily squirrels under these circumstances. rel control, read the product label to feed on seeds during this period. Fumi- determine if any restrictions exist on gation is most effective in spring when LEGAL STATUS AND LEGAL control within the ranges of soil is moist, which helps seal gasses in CONSIDERATIONS these and other endangered and pro- the burrow system. Fumigating at this Ground squirrels are classified as non- tected animals. Also, if the kit fox is time also is more effective because game by the California Fish found in your county (for a range map, squirrels are removed before they can and Game Code. Nongame mammals see the California Department of Pesti- reproduce. Figure 2 shows the yearly injuring growing crops or other prop- cide Regulation’s Web site listed in activities of the California ground squirrel and times when baiting, trap- ping, and fumigation are most effective. winter spring summer fall Major activity periods Trapping adult Traps are practical for control when reproduction squirrel numbers are low to moderate. juveniles Live-catch traps are not recommended because they present the problem of Major food sources how to dispose of the live animals. green forage Because ground squirrels carry dis- seeds eases and are agricultural pests, the best time for control California Fish and Game Code speci- fumigation fies that it is illegal to release them elsewhere without a written permit. baiting trapping There are several types of traps that kill ground squirrels, including box traps, Conibear traps, and tunnel traps. Figure 2. The best time for a specific type of control depends on the activity periods Box traps (Fig. 3) should be placed on and food sources of the ground squirrel. the ground near squirrel burrows or

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and squirrel. With this type of trap, leaving the trap baited but unset has little effect on trapping success.

Inspect traps at least once a day and remove dead squirrels. Do not handle the carcasses without protective gear. Use a plastic bag slipped over each hand and arm as a glove. Once the squirrel is removed from the trap, hold the with one hand and turn the bag inside out while slipping it off your arm and hand. If possible, keep small children and pets out of the area while traps are in use. In kit fox areas, Figure 4. To use a Conibear trap, dig a spring all Conibear traps before night- slice of soil from the entrance so the fall and reset them the following trap will fit flush to the edges of the morning. burrow entrance.

Fumigation 3” Fumigation is a relatively safe method runways. Bait these traps with wal- of control. As with any pesticide, read nuts, almonds, oats, barley, or melon and follow label instructions with par- rinds. Place the bait well behind the ticular regard for nontarget species and Figure 5. A bait box. trigger or tied to it. Bait the traps but safety factors. With some fumigants, do not set them for several days so the flames may be produced, creating a squirrels become accustomed to them. fire danger. Do not use such fumigants which are designed for fumigating After the squirrels are used to taking where a significant fire hazard exists, burrowing rodents. Other types of the bait, rebait and set the traps. such as near buildings, dry grass, or fumigation cartridges are also available other flammable materials. To avoid at retail outlets. Fumigation is most To reduce hazards to children, pets, the accumulation of fumes in enclosed effective in spring or other times when poultry, and nontarget wildlife, place areas, never fumigate beneath build- soil moisture is high, which helps to box-type traps in a covered box with a ings or in burrows that may open un- contain the gas within the burrow sys- 3-inch diameter entrance. Put the box der occupied buildings. tem. Do not fumigate in summer or near active burrows with signs of re- when the soil is dry because the gas cent diggings. Inactive burrows will be Be aware of the signs of nontarget spe- more readily diffuses into small cracks filled with leaves, old straw, or have cies inhabiting inactive ground squirrel present in dry soil. Do not fumigate cobwebs across the entrance. burrows. Kit foxes will use an old bur- during because the squirrel row, enlarging the opening, often cre- plugs its burrow with soil, preventing The Conibear trap (No. 110) with a 41⁄2- ating a keyhole-shaped entrance. fumes from reaching the nest chamber. by-41⁄2-inch jaw spread is also an effec- Active pupping dens may be littered The plug cannot be seen by examining tive kill trap (Fig. 4). The wire trigger with prey remains, droppings, and the burrow entrance. can be baited but is usually left un- matted vegetation, and show signs of baited. Place the trap directly in the fresh paw prints. The Treat all active burrow systems when burrow opening so the squirrel must (Athene cunicularia) is another potential fumigating. When using a USDA gas pass through it, tripping the trigger. It occupant of abandoned ground squir- cartridge, puncture the end with a nail may be necessary to partially fill in the rel burrows. Only fumigate active or screwdriver at the points marked burrow entrance around the outer ground squirrel burrows; county agri- and rotate the nail to loosen the mate- edges of the trap with soil to prevent cultural commissioners can provide rial inside. Insert the fuse into the cen- the squirrel from slipping around the additional information on how to rec- ter hole. Place the cartridge in the outside of the trap. Closing all other ognize these. Do not treat a burrow if burrow as far as possible and light the burrows with soil may hasten success you suspect a nontarget animal is fuse. With a shovel handle or stick, by directing the squirrel to the remain- present. push the lighted cartridge down the ing open burrow with the trap. Attach burrow and quickly seal the opening the Conibear trap to a stake to prevent Many county agricultural commission- with soil, tamping it down. Fill in con- a scavenger from carrying off the trap ers’ offices sell USDA gas cartridges, nected burrows if smoke is seen escap-

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ing. Larger burrow systems usually 200-foot intervals. Initially, inspect bait tors are not able to keep ground squir- require two or more cartridges placed stations daily and add bait as needed. rel populations below the level at in the same or connecting burrow Increase the amount of bait if all is which they become pests for the home openings. After 24 hours, check for eaten by the end of the day. Fresh bait gardener. Dogs may prevent squirrels reopened burrows and re-treat as is important; replace moldy or old bait. from entering small areas, but they needed. Do not use old, leftover bait. It may cannot control established squirrel take a number of days before squirrels populations. Toxic Baits become accustomed to the bait box and Anticoagulant baits, available at enter it. Anticoagulant bait generally Follow-up county agricultural commissioners’ requires 2 to 4 weeks or more to be For those who live next to wildlands or offices, are recommended for control- effective. Continue baiting until all other areas where squirrels are com- ling ground squirrels. To be effective, feeding ceases and no squirrels are mon, an ongoing control program will anticoagulants must be consumed in observed. While few ground squirrels be necessary. Squirrels will reinvade several feedings over a period of 5 or will die aboveground, those that do over time. Once ground squirrels have more days. These features, as well as should be picked up and disposed of been controlled, periodically monitor an antidote (vitamin K1), make antico- as described in the section above on the area for reinfestation. Check for agulant baits relatively safe for humans Trapping and in accordance with label new burrows. Start control actions as and pets. Keep pets out of treated ar- directions. Also, pick up and dispose soon as new squirrels are noticed. It is eas, check the areas daily, and remove of unused bait (according to label in- easier and less expensive to control a and dispose of any carcasses. Dogs are structions) upon completion of the small population. more likely to consume the pelletized control program. cereal-based baits than the loose grain REFERENCES baits. Pelletized baits are prohibited in Modification California Department of Pesticide kit fox areas. Ground squirrels generally are found Regulation. 1995. Protecting Endangered in open areas, although they some- Species: Interim Measures for San Joaquin Anticoagulant baits can be used in bait times use available cover. Remove Kit Fox. Sacramento: Pestic. Regis. boxes or by repeated spot baiting. Bait brush piles and debris to make an area Branch, Pestic. and Toxic Substances boxes are small structures that the less desirable to ground squirrels. This H-7506. 13 pp. For online information, squirrel must enter to eat the bait. also aids in detection of squirrels and see http://www.cdpr.ca.gov/docs/ Boxes contain sufficient bait for re- their burrows, and improves access es/espdfs/sjkfall.pdf or http:// peated feedings. They are the preferred during control operations. www.cdpr.ca.gov/docs/es/espdfs/ baiting method around homes and sjkfden.pdf other areas where children, pets, and Ground squirrels can reinvade a site by poultry are present. moving into vacant burrows. Destroy Clark, J. P. 1994. Vertebrate Pest Control old burrows by deep ripping them to a Handbook. 4th ed. Sacramento: Div. Unless a bait label specifies otherwise, depth of at least 20 inches, using a trac- Plant Industry, Calif. Dept. Food and bait boxes can be constructed from any tor and ripping bar(s). Simply filling in Agric. 350 pp. durable material and in a variety of the burrows with soil does not prevent designs. If you design a bait box, make reinvasion as ground squirrels easily Marsh, R. E. 1994. Belding’s, California, the entrance hole(s) about 3 inches find and reopen old burrows. and rock ground squirrels. In S. E. across to allow access to squirrels but Hygnstrom, R. M. Timm, and G. E. not to larger animals (Fig. 5). Construct Other Control Techniques Larson, eds. Prevention and Control of a lip to prevent bait from spilling out Shooting squirrels with a .22 rifle may Wildlife Damage. Vol. 1. Lincoln: Univ. of the box when squirrels exit. Provide provide some control but is very time- Neb. Coop. Ext. pp. B.151–158. a lock on the box or devise some other consuming. Shooting is recommended method that will make it difficult for only when it can be safely done in ru- Salmon, T. P. and R. E. Lickliter. 1984. children to open. Secure the bait box so ral locations where squirrel numbers Wildlife Pest Control around Gardens and it cannot be turned over or easily re- are very low. There are no effective Homes. Oakland: Univ. Calif. Agric. moved. A self-feeding arrangement frightening devices or repellents that Nat. Res. Publ. 21385. 90 pp. insures that the pest gets a continuous will cause ground squirrels to leave supply of bait. Never fill a bait box their burrows or avoid an area or crop. Tomich, P. Q. 1982. Ground squirrels. with more than 5 pounds of bait. In J. A. Chapman and G. A. Feldhamer, Natural Control eds. Wild Mammals of North America: Place bait boxes near runways or bur- Many predators, including hawks, Biology, Management, and Economics. rows. If squirrels are present over a eagles, rattlesnakes, and , eat Baltimore: Johns Hopkins Univ. Press. large area, space the boxes at 100- to ground squirrels. In most cases, preda- pp. 192–208.

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For more information contact the University of California Cooperative Extension or agri- cultural commissioner’s office in your coun- ty. See your phone book for addresses and phone numbers.

AUTHORS: T. P. Salmon and W. P. Gorenzel EDITOR: B. Ohlendorf TECHNICAL EDITOR: M. L. Flint DESIGN AND PRODUCTION: M. Brush ILLUSTRATIONS: Fig 1: from T. P. Salm- on. 1981. Controlling Ground Squirrels Around Structures, Gardens, and Small Farms. Univ. Calif. Div. Agric. Nat. Res. Leaflet 21179; Figs. 2, 3, 5: adapted from Salmon, T. P., and R. E. Lickliter. 1984. Wildlife Pest Control Around Gardens and Homes. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 21385. Fig. 4: Seventeenth Street Studios

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