Meadow Vole

Microtus pennsylvanicus

Description:

The Meadow Vole (Microtus pennsylvanicus), sometimes called the Field Mouse or Meadow Mouse, is a North American vole found across Canada, Alaska and the northern United States. Its range extends further south along the Atlantic coast. One subspecies, the Florida Salt Marsh Vole (M. p. dukecampbelli), is found in Florida, and is classified as endangered. It is also found in Chihuahua, Mexico. The Meadow Vole is active year-round, usually at night. It also digs underground burrows where it stores food for the winter and females give birth to their young. Although these animals tend to live close together, they are aggressive towards one other. This is particularly evident in males during the breeding season. It can cause damage to fruit trees, garden plants and commercial grain crops. The meadow vole has the widest distribution of any North American species of Microtus. It ranges from Labrador west to Alaska and south from Labrador and New Brunswick to South Carolina and extreme northeastern Georgia; east through Tennessee, Missouri, north-central Nebraska, the northern half of Wyoming, and central Washington to Alaska; south through Idaho into north-central Utah. It is excluded only from the extreme polar regions. A disjunct subset of its range occurs from central Colorado to northwestern New Mexico. Meadow voles are most commonly found in grasslands, preferring moister areas, but are also found in wooded areas. In eastern Washington and northern Idaho meadow voles are found in relative abundance in sedge (Carex spp.) fens but not in adjacent cedar (Thuja spp.)-hemlock (Tsuga spp.), Douglas-fir (Pseudotsuga menziesii), or ponderosa pine (Pinus ponderosa) forests. Meadow voles are also absent from fescue (Festuca spp.)-snowberry (Symphoricarpos spp.) associations. It was speculated that moisture is a major factor in habitat use; possibly the presence of free water is a deciding factor. In southeastern Montana meadow voles were the second most abundant small mammal (after deer mice (Peromyscus maniculatus)) in riparian areas within big sagebrush (Artemisia tridentata)-buffalo grass (Buchloe dactyloides) habitats. Meadow voles are listed as riparian-dependent vertebrates in the Snake River drainage of Wyoming. Raphael compiled 11 studies on small mammals; meadow voles were reported in only 3 of 29 sites in subalpine forests of the central Rocky Mountains. Davis suggested in 1939 that meadow vole range extensions were likely to be related to irrigation practices. Meadow voles are now common in hayfields, pastures, and along ditches in the Rocky Mountain states. In Pipestone National Monument, Minnesota, meadow voles were present in riparian shrublands, tallgrass prairie, and other habitats. In east-central Ohio meadow voles were captured in reconstructed common cattail (Typha latifolia) wetlands. In Virginia meadow voles were least abundant in eastern redcedar (Juniperus virginiana) glades and most abundant in fields with dense grass cover. Meadow voles are active year-round. Meadow voles are active day or night, with no clear 24-hour rhythm in many areas. Most changes in activity are imposed by season, habitat, cover, temperature, and other factors. Meadow voles have to eat frequently, and their active periods (every 2 to 3 hours) are associated with food digestion. In Canada meadow voles are active the first 3 hours after dawn and during the 2- to 4-hour period before sunset. Most of the nonactive period is spent in the nest. Gestation lasts 20 to 23 days. Neonates are pink and hairless, with closed eyes and ears. Fur begins to appear by days, and young are completely furred except for the belly by 7 days. Eyes and ears open by 8 days. Weaning occurs from 12 to 14 days. Young born in spring and early summer attain adult weight in 12 weeks, but undergo a fall weight loss. Young born in late summer continue growing through the fall and maintain their weight through the winter. Maximum size is reached between 2 and 10 months. Typical meadow vole litters consist of 4 to 6 young, with extremes of 1 and 11 young. On average 2.6 young are successfully weaned per litter. Litter size is not significantly correlated with latitude, elevation, or population density. Fall, winter, and spring litters tend to be smaller than summer litters. Reich found that litter size was positively correlated with body size, and is not significantly different in primaparous and multiparous females. Another report stated that primaparous females had fewer young per litter than multiparous females. Litter size was constant in summer breeding periods at different population densities. One captive female meadow vole produced 17 litters in 1 year for a total of 83 young. One of her young produced 13 litters (totalling 78 young) before she was 1 year old. If breeding began in April, it was estimated that 100 pairs of montane voles (Microtus montanus) in 40 acres could create a density of 8,900 voles by September. Patterns of mortality apparently vary among meadow vole populations. According to Banfield the average meadow vole lifespan is less than 1 month because of high nestling and juvenile mortality. The average time that adults are recapturable in a given habitat is about 2 months, suggesting that the average extended lifespan (i.e. how much time adult meadow voles have left) is about 2 months, not figuring in emigration. Getz reported mortality of 88 percent for the first 30 days after birth. Golley reported that postnestling juveniles had the highest mortality rate (61%), followed by young adults (58%) and older age groups (53%). He estimated that nestlings had the lowest mortality rate (50%). Estimated mean longevity ranges from 2 to 3 months to 10 to 16 months. Banfield reported that the maximum lifespan in the wild is 16 months, and Johnson and Johnson stated that few voles live more than 2 years. Meadow vole populations fluctuate annually and also tend to reach peak densities at 2- to 5-year intervals, with population declines in intervening years. Breeding often ceases in January and starts again in March. Over the course of a year, meadow vole populations tend to be lowest in early spring; the population increases rapidly through summer and fall. In years of average population sizes, typical meadow vole population density is about 15 to 45 meadow voles per acre in old-field habitat. In peak years meadow vole population densities may reach 150 meadow voles per acre in marsh habitat (more favorable for meadow voles than old fields). Fritzell stated that peak meadow vole abundance can exceed 1,482 meadow voles per acre (600/ha) in northern prairie wetlands. Meadow voles in optimal habitats in Virginia (old fields with dense vegetation) reached densities of 983 per acre (398/ha); populations declined to 67 per acre (27/ha) at the lowest point in the cycle. Different factors influencing population density have been assigned primary importance by different authors. Reich listed the following factors as having been suggested by different authors: food quality, predation, climatic events, density-related physiological stress, and the presence of genetically determined behavioral variants among dispersing individuals. Normal population cycles do not occur when dispersal is prevented; under normal conditions dispersers have been shown to be behaviorally, genetically, and demographically different from residents. Birney and others hypothesized that there is a threshold density of cover needed for meadow vole populations to increase. Above the threshold amount the quantity of cover influences the amplitude and possibly the duration of the population peak. Local patches of dense cover could serve as source populations or reservoirs to colonize less favorable habitats with sparse cover. Meadow voles form extensive colonies and develop communal latrine areas. They are socially aggressive and agonistic; females dominate males and males fight amongst themselves. As with many other small mammal species, M. pennsylvanicus plays important ecological roles. The meadow vole is an important food source for many predators such as snakes, owls, hawks, and carnivorous mammals. The meadow vole also disperses mycorrhizal fungi. It is a major consumer of grass and disperses grass nutrients in its feces. After disruptive site disturbances such as forest or meadow fires, the meadow vole's activities contribute to habitat restoration. The meadow vole prefers open, non-forest habitats and colonizes such open areas created by fire or other clearing disturbances. Very few meadow voles are found in forest or woodland areas. In newly opened areas, the meadow vole is quite abundant. In these new open areas, the vole quickly becomes a food source for predators.

Habitat:

The meadow vole has the widest distribution of any North American species of Microtus. It ranges from Labrador west to Alaska and south from Labrador and New Brunswick to South Carolina and extreme northeastern Georgia; east through Tennessee, Missouri, north-central Nebraska, the northern half of Wyoming, and central Washington to Alaska; south through Idaho into north-central Utah. It is excluded only from the extreme polar regions. A disjunct subset of its range occurs from central Colorado to northwestern New Mexico. Optimal meadow vole habitat consists of moist, dense grassland with substantial amounts of plant litter. Habitat selection is largely influenced by relative ground cover of grasses and forbs; soil temperature, moisture, sodium, potassium, and pH levels; humidity; and interspecific competition. Meadow voles are most commonly associated with sites having high soil moisture. They are often restricted to the wetter microsites when they occur in sympatry with prairie voles (Microtus ochrogaster) or montane voles. In an Iowa prairie restoration project, meadow voles experienced an initial population increase during the initial stage of vegetation succession (old field dominated by foxtail grass (Setaria spp.), red clover (Trifolium pratense), annual ragweed (Ambrosia artemisiifolia), alfalfa (Medicago sativa), and thistles [Cirsium spp.]). However, meadow vole populations reached their peak abundance during the perennial grass stage of succession from old field to tallgrass prairie. Geier and Best found meadow voles in habitat devoid of tree cover in which grasses dominated the herb layer. They listed the meadow vole as a species with low tolerance for habitat variation (i. e., a species that is intolerant of variations in habitat, is restricted to few habitats, and/or uses habitats less evenly than tolerant species). In most areas meadow voles clearly prefer habitat with dense vegetation. In tallgrass prairie at Pipestone National Monument, meadow voles were positively associated with dense vegetation and litter. Conley and others reported that variables important to meadow vole habitat in Virginia include vegetative cover reaching a height of 8 to 16 inches (20-41 cm) and presence of litter. Meadow voles appeared to be randomly distributed within a grassland habitat in southern Quebec.[29] Grant and Morris[29] were not able to establish any association of meadow vole abundance with particular plant species. They were also unable to distinguish between food and cover as the determining factor in meadow vole association with dense vegetation. In eastern Massachusetts meadow vole density on a mosaic of grassy fields and mixed woods was positively correlated with decreasing vertical woody stem density and decreasing shrub cover. Meadow vole density was highest on plots with more forbs and grasses and less woody cover; meadow voles preferred woody cover over sparse vegetation where grassy cover was not available. In West Virginia the only forested habitats in which meadow voles were captured were seedling stands. In South Dakota meadow voles prefer grasslands to Rocky Mountain juniper (Juniperus scopulorum) woodlands. In New Mexico meadow voles were captured in stands of grasses, wild rose (Rosa spp.), prickly-pear (Opuntia spp.), and various forbs; meadow voles were also captured in wet areas with tall marsh grasses. Open habitat with a thick mat of perennial grass favors voles. In west-central Illinois meadow voles were the most common small mammals on Indian grass (Sorghastrum nutans)-dominated and switchgrass (Panicum virginicus)-dominated study plots. They were present in very low numbers on orchard grass (Dactylis glomerata)-dominated plots. The most stable population of meadow voles occurred on unburned big bluestem (Andropogon gerardii)-dominated plots. In Ontario meadow voles and white-footed mice (Peromyscus leucopus) occur together in ecotones. Meadow voles were the most common small mammals in oak savanna/tallgrass prairie dominated by northern pin oak (Quercus palustris) and grasses including bluejoint reedgrass (Calamagrostis canadensis), prairie cordgrass (Spartina pectinata), big bluestem, switchgrass, and Indian grass. In Michigan strip clearcuts in a conifer swamp resulted in an increase in the relative abundance of meadow voles. Meadow voles were most abundant in clearcut strip interiors and least abundant in uncut strip interiors. Slash burning did not appear to affect meadow vole numbers about 1.5 years after treatment. In Pennsylvania three subadult meadow voles were captured at least 1.6 miles (2.6 km) from the nearest appreciable suitable meadow vole habitat, suggesting that meadow voles are adapted to long-distance dispersal. In Ohio the effects of patch shape and proportion of edge were investigated by mowing strips between study plots. The square plots were 132 feet per side (40m x 40m), and the rectangular patches were 52.8 feet by 330 feet (16m x 100m). Square habitat patches were not significantly different than rectangular patches in meadow vole density. There were no apparent edge effects in patches of this size, suggesting that meadow voles are edge-tolerant. Habitat patch shape did affect dispersal and space use behaviors. In rectangular patches home ranges were similar in size to those in square patches, but were elongated. Meadow voles tend to remain in home ranges and defend at least a portion of the home range from conspecifics. Home ranges overlap and have irregular shapes. Meadow vole home range size depends on season, habitat, and population density: ranges are larger in summer than winter, ranges in marshes are larger than ranges in meadows, and ranges are smaller at higher population densities. Home ranges vary in size from 0.08 to 2.3 acres (0.32-0.9 ha). Females have smaller home ranges than males, but are more highly territorial than males; there is often a period when juveniles from one litter are still present in the adult female's home range when the next litter is borne. Female territoriality tends to determine density in suboptimal habitats; the amount of available forage has been suggested as the determining factor in female territory size and therefore also determines reproductive success.