John M. O’Brien Agricultural Programs Coordinator Nevada Department of Agriculture VOLES Reno, Nevada 89510 Fig. 1. Pine vole, Microtus pinetorum (left), and prairie vole, M. ochrogaster (right). Identification Damage Prevention and Toxicants Voles, also called meadow mice or Zinc phosphide. Control Methods field mice, belong to the genus Exclusion Anticoagulants (registered in most Microtus. Voles are compact rodents states). with stocky bodies, short legs, and Recommended to protect trees, orna- short tails. Their eyes are small and Fumigants mental plants, and small areas. their ears partially hidden. Their Habitat Modification Not usually effective. underfur is generally dense and Trapping covered with thicker, longer guard Eliminating ground cover reduces hairs. They usually are brown or gray, populations. Mouse snap traps. though many color variations exist. Soil cultivation destroys burrows and Live traps (Sherman or box-type There are 23 vole species in the United reduces cover. traps). States. This chapter provides range Frightening Shooting maps, descriptions, and habitat charac- teristics for seven species that are Not effective. Not practical or effective. widespread or cause significant eco- Repellents nomic damage. Tentative identification of a particular animal may be made Effectiveness uncertain. using this information. For positive identification, use a field guide or con- tact an expert. PREVENTION AND CONTROL OF WILDLIFE DAMAGE — 1994 Cooperative Extension Division Institute of Agriculture and Natural Resources University of Nebraska - Lincoln United States Department of Agriculture Animal and Plant Health Inspection Service Animal Damage Control B-177 Great Plains Agricultural Council Wildlife Committee Prairie Vole (Microtus ochrogaster). The prairie vole is 5 to 7 inches (13 to 18 cm) in total length (nose to tip of tail). Its fur is gray to dark brown and mixed with gray, yellow, or hazel- tipped hairs, giving it a “peppery” appearance. Underparts are gray to yellow-gray. It is the most common vole in prairie habitats. Meadow Vole (M. pennsylvanicus). The meadow vole is the most widely distributed Microtus species in the United States. Its total length is 5 1/2 to 7 1/2 inches (14 to 19 cm) and its fur Fig. 2. Distribution of the prairie vole in North Fig. 3. Distribution of the meadow (light) and is gray to yellow-brown, obscured by America. California voles (dark) in North America. black-tipped hairs. Northern subspe- cies may also have some red in their fur. Its underparts are gray, at times washed with silver or buff. The tail is bicolored. Long-tailed Vole (M. longicaudus). The long-tailed vole can be distin- guished from other Microtus species by its tail, which comprises 30% or more of its total length of 6 to 8 1/2 inches (15 to 21 cm). The long-tailed vole has gray to dark brown fur with many black-tipped hairs. The underparts are gray mixed with some white or yel- low. The tail is indistinctly to sharply bicolored. Fig. 4. Distribution of the long-tailed vole in Fig. 5. Distribution of the pine (light), montane Pine or Woodland Vole (M. pine- North America. (medium), and Oregon voles (dark) in North America. torum). The pine vole is a small vole. Its total length is 4 to 6 inches (10 to 15 cm). Its brown fur is soft and dense. to 20 cm) in total length. Its fur is humans, such as orchards, wind- The underparts are gray mixed with tawny olive to cinnamon brown with breaks, and cultivated fields, especially some yellow to cinnamon. The tail is brown to black overhairs. The under- when vole populations are high. Char- barely bicolored or unicolored. parts are grayish. The tail is bicolored. acteristic habitat descriptions for the seven described species follow. Montane (or Mountain) Vole (M. montanus). The montane vole is 5 1/2 Range Prairie Vole. The prairie vole, as the to 8 1/2 inches (15 to 20 cm) in total name suggests, is the most common length. Its fur is brown, washed with Figures 2, 3, 4, and 5 show the approxi- vole of the Great Plains grasslands. It gray or yellow, and mixed with some mate ranges of these species. is found in a variety of habitats, such black-tipped hairs. Its feet are usually as old fields, marshlands, and grass silver-gray and its body underparts prairies. When in association with the are whitish. The tail is bicolored. Habitat meadow vole, it is generally in drier habitats. Oregon Vole (M. oregoni). The Oregon Voles occupy a wide variety of habi- vole is 5 1/2 to 6 1/2 inches (14 to 16 Meadow Vole. The meadow vole is tats. They prefer areas with heavy cm) in length. Its fur is gray to brown found in the northern United States ground cover of grasses, grasslike or yellow-brown. Underparts are and Canada. It prefers wet meadows plants, or litter. When two species are darkish, washed with yellow to white. and grassland habitats. When in asso- found together in an area, they usually The tail is indistinctly bicolored. ciation with the montane vole or occupy different habitats. Though prairie vole, it is generally in moister voles evolved in “natural” habitats, California Vole (M. californicus). The habitats. California vole is 6 to 8 1/2 inches (15 they also use habitats modified by B-178 Long-tailed Vole. The long-tailed entrances. A single burrow system (10,000/ha) in some instances during a vole is found in a wide variety of habi- may contain several adults and young. 1957 to 1958 irruption. tats (for example, sagebrush grass- Voles may breed throughout the year, Many voles are excellent swimmers. lands, forests, mountain meadows, but most commonly in spring and The water vole, in fact, escapes preda- and stream banks) in the western summer. In the field, they have 1 to 5 tors by swimming and diving. The United States and Canada. litters per year. They have produced climbing ability of voles varies. The Pine Vole. The pine vole is found in up to 17 litters per year in a laboratory. long-tailed vole, for example, is a good the eastern United States. It inhabits a Litter sizes range from 1 to 11, but usu- climber (Johnson and Johnson 1982) variety of habitats such as deciduous ally average 3 to 6. The gestation while the pine vole is a bit clumsy in and pine forests, abandoned fields, period is about 21 days. Young are this regard. and orchards. Heavy ground cover is weaned by the time they are 21 days Voles are prey for many predators (for characteristic of these habitats. old, and females mature in 35 to 40 example, coyotes, snakes, hawks, owls, days. Lifespans are short, probably Montane Vole. The montane vole is and weasels); however, predators do ranging from 2 to 16 months. In one found primarily in mountainous not normally control vole populations. population, there was 88% mortality regions of the western United States. during the first month of life. It is found in alpine meadows, dry Damage and Damage grasslands, and sagebrush grasslands. Large population fluctuations are Identification It avoids forests. When in association characteristic of voles. Population with the meadow vole, it is generally levels generally peak every 2 to 5 in drier habitats. years; however, these cycles are not Voles may cause extensive damage to predictable. Occasionally during popu- orchards, ornamentals, and tree Oregon Vole. The Oregon vole is lation irruptions, extremely high vole plantings due to their girdling of seed- most often found in forested areas of densities are reached. Dispersal, food lings and mature trees. Girdling dam- northern California, Oregon, and quality, climate, predation, physiologi- age usually occurs in fall and winter. Washington where there is an under- cal stress, and genetics have been Field crops (for example, alfalfa, clo- story of forbs and grasses such as in shown to influence population levels. ver, grain, potatoes, and sugar beets) burned or clear-cut areas. Other factors probably also play a part. may be damaged or completely California Vole. The California vole destroyed by voles. Voles eat crops Population densities are variable. inhabits the chaparral woodland and also damage them when they Smolen and Keller (1987) list densities shrubland of California. It is found in build extensive runway and tunnel of long-tailed vole populations. A Cali- both wet and well-drained areas. systems. These systems interfere with fornia population ranged from about 2 crop irrigation by displacing water and to 7 voles per acre (5 to 16/ha) and a causing levees and checks to wash out. Food Habits New Mexico population ranged from Voles also can ruin lawns, golf courses, Voles eat a wide variety of plants, around 8 to 49 voles per acre (20 to and ground covers. 121/ha). Cole and Batzli (1979) found most frequently grasses and forbs. In Girdling and gnaw marks alone are late summer and fall, they store seeds, that prairie vole populations averaged 15 per acre (38/ha) in prairie, 52 per not necessarily indicative of the pres- tubers, bulbs, and rhizomes. They eat ence of voles, since other animals, such bark at times, primarily in fall and acre (128/ha) in bluegrass, and 99 per acre (244/ha) in alfalfa. Another vole as rabbits, may cause similar damage. winter, and will eat crops, especially Vole girdling can be differentiated when their populations are high. population ranged from 1 to 14 per acre (2 to 35/ha) over 3 years in west- from girdling by other animals by the Occasional food items include snails, non-uniform gnaw marks. They occur insects, and animal remains. ern mixed prairie. Variability in meadow vole population density was at various angles and in irregular reported by Taitt and Krebs (1985).