Voles are small rodents that measure 4 to 8.5 inches long and weigh 0.8 to 3 ounces and vary in color from brown to gray. They are pudgy, with blunt faces and small eyes, small and sometimes inconspicuous ears, short legs, and a short (the long-tailed vole is an exception) and scantily haired tail.
Eight species of voles are found widely throughout various ecosystems of Colorado, in heavy ground cover of grasses, grass-like plants, and litter.
- Eight species of voles are found in Colorado. They often are called meadow, field or pine mice.
- Voles are small mammals that cause damage by girdling seedling and mature trees in orchards, shelterbelts and forests. They also damage field crops and frequently construct runways in lawns.
- Damage by voles can be reduced by habitat modification, exclusion, repellents, trapping, and poison grain baits.
Biology, Reproduction and Behavior
Voles are active day and night throughout the year and do not hibernate. They usually live between two and six months. Their home ranges usually are less than one-fourth acre and vary with season, food supply and population density. Voles construct many surface runways and underground tunnels with numerous burrow entrances. A single burrow may contain several adults and young.
Population densities of voles vary from species to species. Large population fluctuations that range from 14 to 500 voles per acre are common. Their numbers generally peak every three to five years. Population is influenced by dispersal, food quality, climate, predation, physiological stress, and genetics.
Voles have three to six young per litter and three to 12 litters per year. Their gestation period ranges from 20 to 23 days and they breed almost year around, although most reproduction occurs in spring, summer and fall. Females may become pregnant at three weeks of age.
Damage and Control
Voles can cause extensive damage to forests, orchards and ornamental plants by girdling trees and shrubs. They prefer the bark of young trees but will attack 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.
Damage to crops, such as alfalfa, clover, potatoes, carrots, beets and turnips is common and most evident when voles are at high population levels. Runways and tunnel systems constructed in agricultural fields can divert irrigation water. Voles often damage lawns and golf courses by constructing runways and burrow systems.
Vole damage to trees and shrubs is characterized by girdling and patches of irregular patterns of gnaw marks about 1/16 to 1/8-inch wide. Gnawed stems may have a pointed tip. Do not confuse vole damage with damage by rabbits, which includes stems clipped at a smooth 45-degree angle and wider gnaw marks. Stems browsed by deer usually have a rough jagged edge.Voles also girdle the roots of trees and shrubs.
Other signs of damage by voles include: 1) 1- to 2-inch-wide runways through matted grass and burrows; 2) visual sightings; 3) hawks circling overhead and diving into fields; and 4) spongy soil from burrowing activity. Trees that appear to suffer from disease or insect infestation may be suffering from unseen vole damage.
Methods to prevent and control damage are: habitat management, exclusion, repellents, trapping, and poison grain baits. Voles are classified as non-game wildlife in Colorado and may be captured or killed when they create a nuisance or cause property damage.
Habitat Management. Elimination of weed ground cover and tall grasses by frequent and close mowing, tilling, or herbicide application is the most successful and longest lasting method to reduce vole damage to orchards. This will diminish the amount of available habitat and reduce their numbers. Prunings left in orchards prevent proper mowing and provide a temporary food source, which may lead to damage by voles. Planting short grasses that do not mat or lodge, such as buffalo grass, blue grama, or dwarf fescues, will provide little protective cover and may reduce vole numbers.
Meadow voles are active during the day within their runways under thick grass and vegetation. Summer removal of vegetation (2 feet of trunks of fruit trees) provides some protection because voles avoid exposed areas.
Damage to lawns can be reduced by close mowing in the fall before snow arrives and by mowing and removing tall grassy cover near lawns. To repair damage to lawns from runway construction, rake, fertilize and water the effected area. Close mowing and weed control in grassy borders adjacent to agricultural crops will reduce the habitat for voles and should reduce damage. If suitable, plant crown vetch (a legume unpalatable to voles) in orchard and field boundaries to reduce vole populations.
Important predators of voles are: short-tailed shrews, badgers, coyotes, foxes, bobcats, barn owls, great horned owls, long-eared owls, short-eared owls, barred owls, screech owls, and some snakes. Predators will not likely keep an orchard vole-free, but they can help reduce the vole population. Orchardists should tolerate predators and protect them if they do not constitute a pest problem.
Exclusion
To protect against vole damage, encircle young trees and shrubs with 1/4-inch mesh hardware cloth or 3-inch diameter Vexar plastic-mess cylinders. 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.