Meadow Vole - Reproduction

Reproduction

Gestation lasts 20 to 23 days. Neonates are pink and hairless, with closed eyes and ears. Fur begins to appear by three days, and young are completely furred except for the belly by seven days. Eyes and ears open by eight 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 two and 10 months.

Typical meadow vole litters consist of four to six young, with extremes of one 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. Litter size was positively correlated with body size, and is not significantly different in primaparous and multiparous females. Primaparous females had fewer young per litter than multiparous females. Litter size was constant in summer breeding periods at different population densities. Female meadow voles reach reproductive maturity earlier than males; some ovulate and become pregnant as early as three weeks old. Males are usually six to eight weeks old before mature sperm are produced. One captive female produced 17 litters in one year for a total of 83 young. One of her young produced 13 litters (totalling 78 young) before she was a year old., !-- not this species If breeding began in April, an estimated 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. The average meadow vole lifespan is less than one month because of high nestling and juvenile mortality. The average time adults are recapturable in a given habitat is about two months, suggesting the average extended lifespan (i.e. how much time adult meadow voles have left) is about two months, not figuring in emigration. Mortality was 88% for the first 30 days after birth,. and postnestling juveniles had the highest mortality rate (61%), followed by young adults (58%) and older age groups (53%). Nestlings were estimated to have the lowest mortality rate (50%). Estimated mean longevity ranges from two to 16 months. The maximum lifespan in the wild is 16 months, and few voles live more than two years.

Meadow vole populations fluctuate annually and also tend to reach peak densities at two- to five-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, their population densities may reach 150 per acre in marsh habitat (more favorable for meadow voles than old fields). 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. A threshold density of cover is thought to be 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.