Six species of voles of the genus Microtus occur in California. They are collectively called meadow mice or voles. Two species of voles are responsible for the majority of damage. The California vole (Microtus californicus) is the most widespread vole in the state, found in the Owens and Central valleys and nearly the entire length of the coast range. The montane vole (M. montanus) inhabits northeastern California and the eastern Sierra slope. Voles do not commonly invade homes, and should not be confused with the house mouse, Mus musculus.
Voles are intriguing small mammals because some populations regularly go through cycles from low to high numbers with occasional irruptions that can send numbers soaring (up to several thousand per acre).
IDENTIFICATION
Voles are mouse like rodents somewhat similar in appearance to pocket gophers. They have a compact, heavy body, short legs, short-furred tail, small eyes, and partially hidden ears. The long, coarse fur is blackish brown to grayish brown. When fully grown they can measure 5 to 8 inches long, including the tail.
Although voles do spend considerable time aboveground and may occasionally be seen scurrying about, most of their time is spent below ground in their burrow system. 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 burrow openings that are each about 1-1/2 to 2 inches in diameter. The runways are easily found by pulling back overhanging ground cover. Fresh clippings of green grass and greenish-colored droppings about 3/16 inch long in the runways and near the burrows are further evidence of voles. With age, the droppings lose the green coloring and turn brown or gray.
BIOLOGY AND BEHAVIOR
Voles are active day and night, year-round. They are normally found in areas with dense vegetation. Voles dig many short, shallow burrows and make underground nests of grass, stems, and leaves. In areas with winter snow, voles will burrow in and through the snow to the surface.
Several adults and young may occupy a burrow system. Home-range size varies with habitat quality, food supply, and population levels, but in most cases it is no more than a few hundred square feet.
Vole numbers fluctuate from year to year; under favorable conditions their populations can increase rapidly. In some areas their numbers are cyclical, reaching peak numbers every 3 to 6 years before dropping back to low levels. Voles may breed any time of year, but the peak breeding period is spring. Voles are extremely prolific with females maturing in 35 to 40 days and having five to ten litters per year. Litter size ranges from three to six. However, voles seldom live past 12 months of age.
Voles are mostly herbivorous, feeding on a variety of grasses, herbaceous plants, bulbs, and tubers. They eat bark and roots of trees, usually in fall or winter. Voles store seeds and other plant matter in underground chambers.
Voles are poor climbers and do not usually enter homes or other buildings. Instead, they inhabit wildlands or croplands adjacent to buildings, or gardens and landscaped sites with protective ground cover. Most problems around homes and gardens occur during outbreaks of vole populations.
_______________________________________________________________________________
