Managing Voles in Colorado Fact Sheet No. 6.507 Natural Resources Series|Wildlife By W.F. Andelt, S. Ahmed and K. Jones1 (6/09) Montane voles (Microtus 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 rodents that measure 4 • Eight species 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 vole • Voles are small mammals 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 plants, and litter. Figure 3: Montane vole 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: Meadow vole 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 tunnel 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 burrow population density. Voles construct systems. many surface runways and underground Vole damage to trees and shrubs is Figure 6: Prairie vole distribution.3 tunnels 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, predation, 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 burrows; gestation period ranges from 20 to 23 2) visual sightings; 3) hawks circling days and they breed almost year around, overhead and diving into fields; and 4) Figure 7: Sagebrush vole 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. insect 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 coyotes, foxes, bobcats, be captured or killed when they create a weasels, snakes and several species nuisance or cause property damage. of owls 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 heather vole 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 tooth marks, all under especially during fall and winter. While forests, orchards and ornamental plants what was the snow 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 plant. to lawns from runway construction, rake, Another product that is available fertilize and water the affected area.