Microtus pennsylvanicus (Ord, 1815)

Nomenclature

The eastern meadow vole, scientifically named Microtus pennsylvanicus (Ord, 1815), is sometimes referred to as the field mouse or meadow mouse.

General Distribution

It is a North American vole species found in eastern Canada and the United States, with its range extending further south along the Atlantic coast.

Taxonomic History

The western meadow vole, Florida salt marsh vole, and beach vole were previously classified as regional variants or subspecies of M. pennsylvanicus, but all are now recognized as separate species.

Activity Pattern

Eastern meadow voles are active year-round, most often at night.

Burrow Use

They dig burrows that they use to store food for winter, and where females give birth to their young.

Conspecific Behavior

While these animals typically live close to one another, they are aggressive toward conspecifics, a trait that is especially noticeable in males during the breeding season.

Economic Impact

Eastern meadow voles can cause damage to fruit trees, garden plants, and commercial grain crops.

Detailed Geographic Range

The eastern meadow vole occurs throughout eastern North America, ranging from Labrador and New Brunswick south to South Carolina and the extreme northeastern part of Georgia, and west through Tennessee to Ohio.

Range Replacement

West of Ohio, it is replaced by the western meadow vole.

Island Subspecies

Several subspecies, including the beach vole (M. p. breweri) and the extinct Gull Island vole, live on eastern islands.

Optimal Habitat

Optimal habitat for the eastern meadow vole is moist, dense grassland with large amounts of plant litter.

Habitat Selection Drivers

Habitat selection is mainly shaped by the relative ground cover of grasses and forbs, soil temperature, moisture, sodium, potassium, and pH levels, humidity, and interspecific competition.

Soil Moisture Preference

Eastern meadow voles are most commonly found at sites with high soil moisture.

Sympatric Habitat Partitioning

When they share habitat with prairie voles (Microtus ochrogaster) or montane voles, they are often restricted to wetter microsites.

Massachusetts Habitat Density Correlates

In eastern Massachusetts, eastern meadow vole density in a mosaic of grassy fields and mixed woods was positively correlated with lower vertical woody stem density and lower shrub cover.

Massachusetts Cover Preference

Density was highest on plots with more forbs and grasses and less woody cover; when grassy cover was not available, eastern meadow voles preferred woody cover over sparse vegetation.

West Virginia Habitat Occurrence

In West Virginia, eastern meadow voles were only captured in seedling stand forested habitats.

Long-Distance Dispersal Evidence

In Pennsylvania, three subadult eastern meadow voles were captured at least 1.6 miles (2.6 km) from the nearest notable suitable habitat for the species, suggesting they are adapted for long-distance dispersal.

Ohio Patch Shape Study Design

In Ohio, researchers investigated the effects of patch shape and proportion of edge by mowing strips between study plots.

Study Plot Dimensions

The square plots were 132 feet per side (40 m x 40 m), while rectangular patches measured 52.8 feet by 330 feet (16 m x 100 m).

Patch Shape Density Results

Eastern meadow vole density did not differ significantly between square and rectangular habitat patches, and edge effects were not detected for patches of this size, indicating the species is edge-tolerant.

Patch Shape Behavior Impact

Habitat patch shape did impact dispersal and space use behaviors: in rectangular patches, home ranges had a similar size to those in square patches but were elongated.

Home Range Defense

Eastern meadow voles generally stay within their home ranges and defend at least part of their home ranges from other members of the species.

Home Range Characteristics

Home ranges overlap and have irregular shapes.

Home Range Size Drivers

Home range size depends on season, habitat, and population density: ranges are larger in summer than in winter, ranges in marshes are larger than those in meadows, and ranges are smaller when population density is higher.

Home Range Size Range

Home ranges vary in size from 0.08 to 2.3 hectares (0.32–0.9 acres).

Sex-Specific Home Range Traits

Females have smaller home ranges than males, but are more territorial than males; often, juveniles from one litter are still in the adult female's home range when the next litter is born.

Female Territoriality Effects

Female territoriality tends to determine density in suboptimal habitats; the amount of available forage may determine female territory size, and thus reproductive success.

Gestation Period

Gestation for the eastern meadow vole lasts 20 to 23 days.

Newborn Morphology

Newborn voles are pink and hairless, with closed eyes and closed ears.

Juvenile Development First Week

Fur starts to grow by three days of age, and young are fully furred except for the belly by seven days.

Weaning Timeline

Eyes and ears open by eight days, and weaning takes place between 12 and 14 days.

Spring/Summer Juvenile Growth

Young born in spring and early summer reach adult weight in 12 weeks, but lose weight in the fall.

Late Summer Juvenile Growth

Young born in late summer continue growing through the fall and keep their weight through the winter.

Maximum Age for Full Size

Maximum size is reached between two and 10 months of age.

Litter Size Range

Typical litters of eastern meadow voles contain four to six young, with a minimum of one and a maximum of 11 young per litter.

Weaning Success Rate

On average, 2.6 young are successfully weaned per litter.

Litter Size Correlates Part 1

Litter size is not significantly correlated with latitude, elevation, or population density.

Seasonal Litter Size Variation

Litters born in fall, winter, and spring tend to be smaller than summer litters.

Litter Size Correlates Part 2

Litter size is positively correlated with female body size, and does not differ significantly between first-time breeding females and females that have bred before.

First-Time Breeder Litter Size

First-time breeding females have fewer young per litter than females that have bred before.

Summer Litter Size Consistency

Litter size stays consistent during summer breeding periods across different population densities.

Sex-Specific Reproductive Maturity

Female eastern meadow voles reach reproductive maturity earlier than males; some ovulate and become pregnant as early as three weeks old.

Male Reproductive Maturity

Males usually do not produce mature sperm until they are six to eight weeks old.

Captive Reproductive Record Part 1

One captive female produced 17 litters in one year, totaling 83 young.

Captive Reproductive Record Part 2

One of her offspring produced 13 litters (totaling 78 young) before reaching one year old.

Mortality Variability

Mortality patterns vary across eastern meadow vole populations.

Average Lifespan

The average lifespan of an eastern meadow vole is less than one month, due to high mortality among nestlings and juveniles.

Adult Recapture Period

The average period that adults can be recaptured in a given habitat is about two months, which suggests the average remaining lifespan for adult eastern meadow voles is about two months, not accounting for emigration.

First Month Mortality Rate

Mortality is 88% in the first 30 days after birth.

Age-Specific Mortality Rates

Post-nestling juveniles have the highest mortality rate at 61%, followed by young adults at 58%, older age groups at 53%, and nestlings have the lowest estimated mortality rate at 50%.

Longevity Range

Estimated mean longevity ranges from two to 16 months.

Maximum Lifespan

The maximum lifespan in the wild is 16 months, and very few voles live more than two years.

Population Cycle Period

Eastern meadow vole populations fluctuate every year, and generally reach peak densities at intervals of two to five years, with population declines in the years between peaks.

Breeding Season Timing

Breeding often stops in January and restarts in March.

Annual Population Trend

Over the course of a year, eastern meadow vole populations are typically lowest in early spring, and increase rapidly through summer and fall.

Average Old-Field Density

In years with average population sizes, typical population density in old-field habitat is around 15 to 45 voles per acre.

Peak Marsh Density

In peak years, densities can reach 150 voles per acre in marsh habitat, which is more favorable for the species than old fields.

Northern Prairie Peak Density

Peak abundance can exceed 1,482 voles per hectare (600 per acre) in northern prairie wetlands.

Virginia Density Cycle Extremes

In optimal habitats in Virginia (old fields with dense vegetation), densities reached 983 voles per hectare (398 per acre); populations declined to 67 per hectare (27 per acre) at the lowest point of their population cycle.

Proposed Density Drivers

Different authors have identified different primary factors influencing population density.

Reich's Listed Density Factors

Reich listed the following factors that have been proposed by other authors: food quality, predation, climatic events, density-related physiological stress, and the presence of genetically determined behavioral variants among dispersing individuals.

Dispersal Role in Cycles

Normal population cycles do not occur when dispersal is prevented; under normal conditions, dispersers are behaviorally, genetically, and demographically different from resident voles.

Vegetation Cover Threshold

It is thought that a threshold density of vegetation cover is required for eastern meadow vole populations to increase.

Cover Effect on Population Peaks

Above this threshold, the amount of cover influences how large the population peak is and possibly how long it lasts.

Source Population Function

Local patches of dense cover can act as source populations or reservoirs to colonize less favorable habitats with sparse cover.

Social Behavior Part 1

Eastern meadow voles form extensive colonies and develop shared communal latrine areas.

Social Behavior Part 2

They are socially aggressive and agonistic; females dominate males, and males fight with one another.