Voles are small rodents resembling mice measuring 4 to 8.5 inches in length weighing 0.8 to 3 ounces. Commonly called meadow mice or field mice, they are easily recognized by their short tail (about one inch long, with the long tale vole as the exception), a stocky build and small eyes. Although voles are troublesome in the garden they are an important food source for many local predators including coyote, snake, fox and owl.
The good news to gardeners is that Voles have extremely short life spans, 8 weeks to 16 months. However, that means voles have a high reproduction rate. Because of this it is important to remember if you decide to use a chemical pesticide (a short-term solutions) for vole control you will be reapplying toxic chemicals to your yard multiple times per season. These chemicals also affect other ecosystems so please read label entirely prior to application.
Voles breed throughout the year, with peaks occurring during spring and summer. Voles can produce 3 to 12 litters per year with 3 to 5 being the average. Litters range in size from 1 to 11 young per litter, with 3 to 6 being the average. Although gestation periods vary slightly among species, 21 days is the average length of gestation for voles. Young are weaned by the time they are 21 days old, and females are sexually mature within 40 days. A voles home range is usually less than 1/4 acre and vary with season, food supply and population density. 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 3 to 5 years. Factors that influence population levels include dispersal rates, food quality, climate, predation, physiological stress, and genetics.Voles occupy a wide variety of habitats, depending on the species. Generally, voles prefer areas with heavy ground cover of grasses, grass-like plants, or litter. They are active both day and night and throughout the year. Voles eat a variety of plants and animals. They frequently forage on grasses, roots, bulbs, tubers, bark, snails, and insects. To find food, voles construct tunnels and surface runways with many burrow openings. Several adults and young can live in these runway systems. This intricate network of tunnels and burrows provide voles with excellent shelter from the weather and protection from predators. Voles store seeds and other plant matter in underground chambers.
SURFACE RUNWAY SYSTEM OF THE VOLE:
So how do you know if you have voles? If you’re asking yourself this you probably don’t have a vole problem. The clearest signs of their presence are the well-traveled, aboveground runways that connect burrow openings; the runways are usually hidden beneath a protective layer of grass or other ground cover. The maze of runways leads to multiple open burrows that are each about 1 1/2 to 2 inches in diameter. The runways are easily found by pulling back overhanging ground cover.
DAMAGE CAUSED BY VOLES:
Voles can cause extensive damage. 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. Voles may eat landscape plantings such as lilies and dichondra. 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.Fortunately, voles pose no major public health problems because of infrequent contact with humans. However, they can harbor disease organisms, such as plague and tularemia. For this reason, voles should never be handled. If you have to handle a vole, or any other species of wildlife, you should wear the appropriate protective clothing (e.g., leather gloves).
Methods to prevent and control damage are habitat management, exclusion, repellents, trapping, and poison 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. Destroying old runways or burrows to deter immigration of new voles to the site is one of the most important components to vole control.
This is the best long-term solution for vole control. The elimination of weeds, ground cover, and litter around lawns and ornamental plantings can reduce habitat suitability for voles and lead to a decreased likelihood of vole damage. Additionally, soil cultivation destroys vole runway-systems and may kill voles outright. For these reasons, plots of annual plants often are less susceptible to vole damage than perennial plants.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 affected area (see a nursery associate for lawn care & fertilizing timetable).
Cylinders made of hardware cloth (available at most hardware stores) are often effective in excluding voles and protecting individual plants. The mesh size of the hardware cloth used to construct cylinders should be no larger than 1/4 inch in size. The cylinder should be buried at least 6 inches below the ground surface to ensure that voles will not burrow under the hardware cloth and gain access to the plant and should project 18 inches above the ground.
When voles are not numerous or when the population is concentrated in a small area, trapping is effective. Use a sufficient number of traps to control the population: for a small garden a dozen traps is probably the minimum number required, and for larger areas at least 50 or more may be needed. A simple, wooden mousetrap baited with a peanut butter-oatmeal mixture or apple slice is commonly used. Voles seldom stray from their runways so set traps along these routes. Look for burrows and runways in grass or mulch in or near the garden or flowerbeds. Place baited traps at right angles to the runways with trigger end in the runway. Often, no bait is needed because voles will trigger the trap as they pass over it.
Examine traps daily and remove dead voles or reset sprung traps as needed. Continue to trap in one location until no further voles are caught, then move the traps to a new location 15 to 20 feet away. Remember to destroy old runways to prevent other voles from moving in.
*Rodenticides usually are short-term solution to damage by voles. Habitat management usually is more long-term.
Two- percent zinc phosphide baits are available in pellet form. Be sure to follow label direction carefully when using any poison bait.
The best time of year to use zinc phosphide baits on lawns is during fall before snow cover. Unpredictable rain and snowfall will severely limit the life span of baits exposed to the elements. To minimize hazards to birds, do not apply zinc phosphide bait to bare ground, areas without vegetation, or in piles. Also, do not apply to crops destined for use as food or feed. Further, Zinc phosphide can be absorbed in small amounts through human skin. Wear rubber gloves to avoid contact with the chemical and take extra care to avoid breathing zinc phosphide dust.
Many predators, including coyotes, foxes, badgers, cats, and especially hawks, and owls eat voles. However, in most cases predators cannot keep vole populations below damaging levels. Many predators have a broad-based diet and readily shift to alternative prey when the number of voles declines. Predators rarely, if ever, take every last vole; thus, a residual population remains. With their astonishing reproductive potential, any remaining voles could repopulate an area in a short period. With this potential, for severe damage, a homeowner or gardener cannot afford to wait for a predator to appear, but must take immediate action to prevent the loss of valuable plantings.
As with all animals, natural constraints limit vole numbers. Because populations will not increase indefinitely, one alternative is to do nothing and let nature limit the voles. Experience has shown, however, that around homes and gardens the natural population peak is too high and damage will be above tolerable limits.
Frightening devices, electromagnetic or ultrasonic devices and flooding have all been shown to be ineffective in reducing vole damage. As well so are fumigants -because the complexity and depth of vole runways and burrows allow the fumigant to escape before voles are exposed to it.*Resources: the City of Denver, Colorado State University.