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Home , Heather vole, Meadow vole, Montane vole, Prairie vole, Sagebrush vole, Vole

Managing in Fact Sheet No. 6.507 Natural Resources Series|Wildlife

By W.F. Andelt, S. Ahmed and K. Jones1 (6/09) Montane voles ( montanus) primarily Revised (11/15) are found in the western half of Colorado Introduction in moist meadows and valleys with thick Quick Facts grass or forb cover from 6,000 feet to above Voles are small that measure 4 • Eight of voles are found to 8 inches long and weigh 0.8 to 3 ounces timberline. in Colorado. They often are and vary in color from brown to gray. They called meadow, field or pine are pudgy, with blunt faces and small eyes, small and sometimes inconspicuous ears, mice. short legs, and a short (the long-tailed • Voles are small that is an exception) and scantily haired tail. cause damage by girdling Eight species of voles are found seedling and mature trees widely throughout various ecosystems of in orchards, shelterbelts and Colorado, in heavy ground cover of grasses, 3 forests. They also damage field grass-like , and litter. Figure 3: distribution. crops and frequently construct Southern red-backed voles (Myodes gapperi) Long-tailed voles (Microtus longicaudus) are runways in lawns. are found in moist and well-developed common over the mountains and high coniferous forests. They are most abundant • Damage by voles can plateaus of the western half of Colorado. in lodgepole pine (Pinus contorta) stands, be reduced by habitat They are most abundant in streamside usually between 8,000 and 11,000 feet. meadows in marshy to dry grassy areas. modification, exclusion, repellents, trapping, and poison grain baits.

Figure 1: Southern red-backed vole Figure 4: Long-tailed vole distribution.3 distribution.3 Mogollon voles (Microtus mogollonensis) Meadow voles (Microtus pennsylvanicus) are found in the very southern part of primarily occur from north to south central Colorado, in Las Animas and Montezuma Colorado and along the South Platte Counties. They occur in ponderosa pine River. They tend to live in or near damp (Pinus ponderosa) woodland or savannah, marshy areas or wet meadows and riparian pinon (Pinus edulis Engelm)–juniper corridors. (Juniperus monosperma and Juniperus scopulorum) woodlands or montane shrublands.

© Colorado State University Extension. 11/95. Revised 11/15. extension.colostate.edu

Figure 2: 3 distribution.3 Figure 5: Mogollon vole distribution.

* Original publication by W.F. Andelt, Colorado State University Extension wildlife specialist and associate professor; and S. Ahmed, former graduate student; fishery and wildlife biology. Reviewed (11/2015)2 Prairie voles (Microtus ochrogaster) are found Damage to crops, such as alfalfa, in grasslands and along streams and Biology, Reproduction pasture grasses, clover, potatoes, carrots, irrigated lands in eastern Colorado. and Behavior beets and turnips is common and Voles are active day and night most evident when voles are at high throughout the year and do not population levels. Runways and hibernate. They usually live between systems constructed in agricultural two and six months. Their home ranges fields can divert irrigation water. Voles usually are less than one-fourth acre often damage lawns and golf courses and vary with season, food supply and by constructing runways and population density. Voles construct systems. many surface runways and underground Vole damage to trees and shrubs is Figure 6: distribution.3 with numerous burrow entrances. characterized by girdling and patches of A single burrow may contain several irregular patterns of gnaw marks about Sagebrush voles (Lemmiscus curtatus) occupy adults and young. 1/16 to 1/8-inch wide. Gnawed stems the driest of all vole habitats in Colorado. Population densities of voles vary may have a pointed tip. Do not confuse Often found in sagebrush habitat, they from species to species. Large population vole damage with damage by rabbits, occur between 5,000 and 9,000 feet in fluctuations that range from 14 to which includes stems clipped at a smooth western and north central Colorado. 500 voles per acre are common. Their 45-degree angle and wider gnaw marks. numbers generally peak every three to Stems browsed by deer usually have a five years. Population is influenced by rough jagged edge. Voles also girdle the dispersal, food quality, climate, , roots of trees and shrubs. physiological stress, and genetics. Other signs of damage by voles Voles have three to six young per include 1) 1 to 2 inch-wide runways litter and three to 12 litters per year. Their through matted grass and ; gestation period ranges from 20 to 23 2) visual sightings; 3) circling days and they breed almost year around, overhead and diving into fields; and 4) Figure 7: distribution.3 although most reproduction occurs in spongy soil from burrowing activity. Trees spring, summer and fall. Females may that appear to suffer from disease or Western heather voles (Phenacomys become pregnant at three weeks of age. infestation may be suffering from intermedius) are found from 7,000 to unseen vole damage. above treeline of central Colorado. They Methods to prevent and control occupy a variety of habitats but are most Ecological Value damage are: habitat modification, abundant along streams. Voles, like many small rodents, are exclusion, repellents, trapping, and an important food source for many poison grain baits. Voles are classified as predators. A variety of predators feed on non-game wildlife in Colorado and may voles including , , , be captured or killed when they create a , and several species nuisance or cause property damage. of and hawks. Caution must be taken when using rodenticides. Zinc phosphide, a restricted use pesticide, is one control method for voles, however, it is extremely toxic and care must be taken to avoid risks to children, pets, and non- Figure 8: Western target wildlife species. Carefully read and distribution.3 follow the label for any rodenticide.

Voles eat a variety of grasses, forbs and agricultural and garden crops. They also Damage and Control Figure 9: Vole damage on lilac. Notice eat bark and roots on trees and shrubs, Voles can cause extensive damage to small, irregular marks, all under especially during fall and winter. While forests, orchards and ornamental plants what was the line. they prefer young, succulent trees and by girdling trees and shrubs. They prefer plants, they can change their diet to meet the bark of young trees but will attack their nutritional needs. any tree, regardless of age, when food is ` scarce. Monitor orchards frequently so control measures can be implemented before appreciable damage occurs. Most damage occurs in the winter when voles move through their grass runways under the protection of snow. The greatest damage seems to coincide with years of heavy snowfall. This barrier should project 18 inches above the ground and 3 to 6 inches below the surface. Vegetable and flower beds may also be protected in this manner.

Repellents Only a few repellents (including Thiram™ and Hot Sauce or capsaicin) are Figure 10: Vole runways in lawn after manufactured to protect trees, shrubs snow melted in spring. and vegetable crops from voles. Little data are available on the effectiveness Figure 14: Examples of vole holes. They of repellents to deter vole damage. will often burrow near a rock, but not However, in one study, Thiram™ was always. reported to reduce damage to apple stems by 78 percent. A 20 percent solution of chicken eggs in water has Habitat Modification been effective in reducing deer and elk High vole populations cannot become browsing and may reduce damage by established without food and lack of voles. predation by predators. Elimination Thiram™ is manufactured by various Figure 11: Vole hole and runway in clay of weed ground cover and tall grasses companies and sold under various trade soil. by frequent and close mowing, tilling, names. Thiram™ products are labeled for or herbicide application is the most protecting most of the following from successful and longest lasting method to voles: tree seedlings, shrubs, ornamental reduce vole damage to orchards. This will plantings, nursery stock, and fruit trees. diminish the amount of available habitat Most labels limit the use of Thiram™ on and reduce their numbers. Prunings left fruit trees to the dormant season. in orchards prevent proper mowing and Capsaicin (the “heat” in spicy provide a temporary food source, which peppers) is labeled for use on may lead to damage by voles. Planting ornamental trees and shrubs, fruit and short grasses that do not mat or lodge, nut trees, fruit bushes and vines, and such as buffalo grass, blue grama, or nursery stock to protect them from Figure 12: Vole hole and runway in snow. dwarf fescues, will provide little protective vole damage. Limit application to Note the oval-shaped OPEN hole. cover and may reduce vole numbers. fruit-bearing plants before fruit sets or Meadow voles are active during the after the fruit is harvested. Hot sauce day within their runways under thick also is registered for use on beans, grass and vegetation. Summer removal of corn, cucumbers, melons, peas, brussel vegetation (2 feet radius around fruit tree sprouts, squash, peppers, tomatoes, trunks) provides some protection because cabbage, and cauliflower before voles avoid exposed areas. edible portions and/or heads begin to Damage to lawns can be reduced form. Capsaicin may burn the leaves by close mowing in the fall before snow on plants. Spray a few leaves first and arrives and by mowing and removing tall check for damage before spraying the grassy cover near lawns. To repair damage whole . to lawns from runway construction, rake, Another product that is available fertilize and water the affected area. Close that is labeled for voles is Ricinis communis mowing and weed management in grassy oil (Castor Oil). Though its effectiveness Figure 13: Examples of vole holes. They borders adjacent to agricultural crops will is not known, it is labeled as safe around will often burrow near a rock, but not reduce the habitat for voles and should children and pets. always. reduce damage. If suitable, plant crown Predator odors, such as the urine vetch (a legume unpalatable to voles) in from red foxes and coyotes, also may be orchard and field boundaries to reduce effective vole repellents. These odors vole populations. are not commercially manufactured, but and urines can be purchased Exclusion from some trapper supply houses. To protect against vole damage, Repellents are relatively expensive and encircle young trees and shrubs with provide short-term protection. They 1/4-inch mesh hardware cloth or 3-inch may wash off during rain and must be diameter Vexar™ plastic-mesh cylinders. reapplied periodically. Trapping • Always locate rodenticides so To prebait, scatter 4 or 6 pounds Use snap traps to that off target species cannot (see label instructions) of untreated oat remove small populations of voles access them (i.e. children, pets, groats, rolled oats or barley (see label from backyard lawns. Place traps wildlife). Use enclosed bait instructions) per acre, two to four days perpendicular to runways with the boxes, make sure rodenticide is before placing a toxic bait. Prebaiting trigger end in the runway and bait with deposited deep enough in the encourages consistent acceptance of small amounts of rolled oats or peanut tunnel or locate them in locked bait. butter. Set traps in the fall before most areas inaccessible to children, When hand baiting around trees, damage occurs. Trapping is not practical pets or wildlife place 1 teaspoon (4 grams) of bait for controlling voles in large areas or on • Never store rodenticides near at two to four locations around each large populations. food items (, pet or tree in surface trails or at the mouth of livestock) holes leading to underground burrow • Follow the label instructions on systems. In non-crop areas, hand baiting Rodenticide Safety carcass surveillance generally consists of placing 1 teaspoon When dealing with any problem, of bait around each active burrow or utilize all management techniques to Poison Grain Baits runway. The most successful control is resolve the problem and do not rely Rodenticides usually are a short- achieved when the bait penetrates the solely on rodenticides. Set realistic goals term solution to damage by voles. grass cover to reach the runways. To such as minimizing the rodent number Habitat modification usually is more broadcast bait, spread 4 to 10 pounds on your property by using exclusion successful than rodenticides for of bait per acre with a cyclone seeder methods, eliminating desirable habitat eliminating damage in orchards. or by hand. Bait also can be spread with or food sources (you’ll never eliminate Two percent zinc phosphide is a trailbuilder. A trailbuilder usually is all voles). When using any rodenticide the most commonly used grain bait pulled by a tractor, creates a burrow in always read and follow the label and for managing voles in Colorado. Zinc the ground and deposits 1 teaspoon guidelines and be sure you understand phosphide is extremely toxic and of bait at 4 to 5 feet intervals. Two to them prior to use to minimize off target care must be taken to avoid risks to 3 pounds of bait per acre usually is (i.e. raptors, , and ) poisoning. children, pets and non-target wildlife. recommended. Rodenticides are meant to kill rodent Zinc phosphide baits are available Zinc phosphide baits are limited for species but will also kill other species if in pellet form (Bell Laboratories’ ZP use only on voles of the Microtus. improperly used. Rodent Bait AG, Chempar’s Ridall Some of the zinc phosphide products • Positively identify the pest and Zinc) on oats (Bell Laboratories’ ZP and/or usages are limited to meadow determine all techniques that can be Rodent Bait AG, USDA/APHIS/ADC voles. used to deter the pest such as habitat Zinc Phosphide on steam-rolled oats) To minimize hazards to birds, do modification and exclusion and on corn (Hopkin’s Zinc Phosphide not apply zinc phosphide bait to bare • Decide what your threshold limit is. Bait). One study indicated that ground, areas without vegetation, or Set realistic goals such as minimizing pelleted zinc phosphide baits provide in piles. Also, do not apply to crops rodent numbers. Do not expect to greater control of voles than zinc destined for use as food or feed. Zinc totally eliminate them phosphide placed on oats or corn. phosphide can be applied to orchards • Choose the most effective, least toxic Most of these baits are labeled for and groves only during the dormant rodenticide use in orchards and groves, nurseries, season after harvest. • If you choose to use a rodenticide, ornamental and non-bearing fruit The best time of year to use zinc • Read and follow the label trees, grapevine yards, and non-crop phosphide baits on lawns is during fall • Abide by any limitation of use areas such as lawns, ornamentals, before snow cover. Application of bait (i.e. use only between Nov. 1 golf courses, and parks. The labeled during spring, after snow melt, usually is and March 30) and other label method of application varies ineffective. restrictions somewhat among manufacturers. Unpredictable rain and snowfall • Wear proper protective clothing However, most of these products will severely limit the lifespan of baits and equipment are labeled for hand baiting, exposed on orchard floors. During wet • Don’t smoke or eat while mixing, broadcast baiting, and/or trailbuilder periods, place baits in jars, metal cans, applying a rodenticide, and wash baiting in orchards and groves, bait stations, polyvinyl-chloride tubes, thoroughly after application nurseries, and ornamental and or under tar paper, shingles, and split • Mix and apply only the quantity non-bearing fruit trees. In grapevine automobile tires. Unfortunately, baits you need yards, these products are labeled placed under these objects and directly • Reference: EPA Citizen’s Guide for broadcast baiting. The Chempar on the ground absorb moisture and to Pesticide Safety http://www. product also is labeled for hand generally do not persist more than two epa.gov/oppfead1/Publications/ baiting. In non-crop areas, these weeks. Cit_Guide/citguide.pdf products are labeled for hand baiting • Always store rodenticides away in conjunction with a prebait. from pets, children and wildlife Because zinc phosphide is toxic to References , store it away from 1W.F. Andelt, Colorado State University and pets. Zinc phosphide can be Extension professor emeritus, absorbed in small amounts through department of fish, wildlife and human skin. Wear rubber gloves to conservation biology; S. Ahmed, avoid contact with the chemical and former graduate student; fishery and take extra care to avoid breathing zinc wildlife biology. 02/03. Reviewed by phosphide dust. Product labels will K. Jones, Extension County Director, contain additional precautions. (4-H/Natural Resources/Agriculture) Anticoagulant baits (warfarin and Chaffee/Park County. 6/09. bromadilone) can also be effective in managing voles. For anticoagulants 2S. Bokan, Small Acreage Coordinator to be effective, it may take multiple Boulder County, K. Crumbaker, Ag applications. Anticoagulants are and Natural Resources Agent Larimer slower acting agents and take 5 - 15 County, T. Hoesli, Extension County days to affect voles. As with zinc Director Grand County, D. Lester, phosphide, place the baits in secure Extension County Director, Park County bait boxes to reduce accidental and and I. Shonle, Extension County secondary poisoning. Always read Director Gilpin County, 11/15 and follow the product label. Fumigants usually do not work for 3 Distribution Maps: Armstrong, David control of voles because their burrows M., James P. Fitzgerald, and Carron A. are too shallow and complex. Meaney. 2011. Mammals of Colorado 2nd ed. Colorado: Denver Museum of & Science and University Press of Colorado.

Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.