Rats, mice, and relatives I

Voles and lemmings (Arvicolinae)

Class Mammalia

Order Rodentia

Suborder Sciurognathi

Family Muridae

Subfamily Arvicolinae

Thumbnail description
Generally small rodents with cylindrical, thickset bodies, and short legs and tails; eyes and ears are normally small and often inconspicuous and the head is broad and rounded

Size
3.5–24.5 in (8.5–62 cm); 0.5 oz to 4 lb (15–1,820 g)

Number of genera, species
26 genera; at least 143 species

Habitat
Forest, woodlands, scrub, grassland, mountains, rivers, and lakes

Conservation status
Critically Endangered: 3 species; Endangered: 2 species; Vulnerable: 4 species; Lower Risk/Conservation Dependent: 1 species; Lower Risk/Near Threatened: 25 species; Data deficient: 7 species; a further 42 subspecies are listed by the IUCN

Distribution
Europe, north, south, and west Asia, and North America

Evolution and systematics

The Muridae is a huge family of more than 1,326 species, the taxonomy of which has long been the subject of considerable and repeated revision. It has previously been considered to comprise a number of separate families, one of which, the Cricetidae, previously included the voles and lemmings. They have also been considered to be a family in their own right, the Arvicolidae, but are currently recognized as one of 17 subfamilies of the Muridae. The junior synonym Microtinae is sometimes used for this subfamily.

The evolutionary origin of voles and lemmings has been the subject of much deliberation. A number of fossil forms are known to have occurred in Asia and North America, but the subfamily has undergone a rapid morphological evolution in the recent past, and the genus Microtus is believed to still be rapidly adapting to fragmentations and new niches. There is very little general consensus over the taxonomy of Microtus, but at least 61 species are currently recognized and the taxonomic status of a number of isolated populations still remains unclear. Many island populations exist that are morphologically distinct from individuals of the same species residing in mainland populations. The Arvicolinae is the third largest subfamily of the family Muridae, containing at least 143 species grouped into 26 genera.

Physical characteristics

Most voles are remarkably consistent in general size, shape, structure, and body form. They are usually small (0.7–2.6 oz [20–75 g]), stocky rodents with compact bodies and short legs and tails, which are generally less than 50% of the head and body length. Most species are some shade of brown with paler ventral surfaces, although there are some exceptions. The high mountain voles (Alticola) are attractive gray, buff, or cream voles with long silky fur. Water voles (Arvicola) and round-tailed muskrats (Neofiber alleni) are similar in general structure to most voles, although considerably larger than all the other species, weighing as much as 15.8 oz (450 g).

The three species of tree vole (Arborimus) are all adapted to an arboreal lifestyle and consequently have much longer tails than the other species of vole, being up to 70–80% of the head and body length. The mole voles (Prometheomys and Ellobius) are the most aberrant of all the voles and, unlike other species, are highly adapted for a fossorial lifestyle. They have cylindrical bodies with very short tails and forward-facing incisor teeth, superficially resembling mole rats in their external morphology.

Lemmings are generally similar to the voles but, in most species, are even more thickset, with stouter, robust bodies and shorter tails. The true lemmings (Lemmus) are highly patterned

with mixtures of buff, gray, white, and brown, while the collared lemmings (Dicrostonyx) have a pure white winter pelage and also develop an enlarged third and fourth claw on the forefeet during the winter, which is unique among rodents.

The muskrat (Ondatra zibethicus) is much larger than any other members of the subfamily. They can weigh as much as 4 lb (1,820 g). Although they are superficially similar to the voles, they are adapted for an aquatic lifestyle, with a proportionally much longer tail that is flattened laterally to act as a rudder. They possess partially webbed feet, which also have fringes of hairs to assist with swimming.

Distribution

Voles and lemmings have a very widespread Holarctic distribution, being found right across temperate North America, Europe, and Asia. Lemmings occur at extreme northern latitudes right up into the Arctic Circle, and a number of vole species are endemic montane specialists. The muskrat is native to North America, although it has been widely introduced in Europe and also into parts of South America.

Habitat

Voles and lemmings occupy a huge range of habitats. Typically, they are associated with open grassland areas and are extremely numerous in the American prairies and Eurasian steppes. Some species such as the red-backed voles (Clethrionomys) or tree voles occur extensively in scrub and woodland, including northern boreal forests. A number of species are endemic to mountain regions and high mountain voles occur up to 19,690 ft (6,000 m) above sea level in the Himalayas.

Water voles and the muskrat are associated with freshwater aquatic habitats, both rivers and still-water lakes. Water voles will even occur in brackish estuarine lagoons and coastal marshes. Lemmings are associated with extreme northern latitudes, occurring in taiga and tundra regions.

Behavior

Voles are both diurnal and nocturnal, and a number of foliage-feeding species such as many of the meadow voles (Microtus) are known to be active on successive cycles of feeding and resting of around four hours duration, both day and night. Species that feed on a higher proportion of seed and insects, such as the red-backed voles (Clethrionomys), tend to have more nocturnal activity patterns. Many of the montane species are mainly diurnal. Lemmings are often active both day and night, with much of the activity in the winter occurring underneath the safety of a thick cover of snow.

A variety of social systems are known in voles and lemmings. One common system that occurs in many species is comprised of mutually exclusive female territories and larger overlapping male territories that vary in location and size in response to receptive females. However, in the field vole (Microtus agrestis) it is the males whose territories are strongly defended and exclusive, while the females have widely overlapping home ranges. Some species of meadow vole are believed to be highly monogamous, and the social systems and the degree of territoriality or tolerance almost certainly vary with density in many of the cyclic species.

Muskrats are territorial, but will live as extended families for periods, sharing the same lodge. When young muskrats do finally disperse, they often move very short distances and establish their own lodges within feet (meters) of the parental territory. The long-clawed mole vole (Prometheomys schaposchnikowi) is reported to live in small groups comprising several reproductive individuals, all sharing the same burrow system along with youngsters. Lemmings often defend just a very small core area that they are using at any one time, which is much smaller than their actual home range, most of which is not territorial.

Some vole species occur at very high densities and, in extreme circumstances, can be as numerous as 1,000–3,000 per 2.5 acres (1 ha). Some meadow vole and red-backed vole species have cyclic populations with peaks every three to five years and, at these peaks, can almost reach plague proportions. Lemmings are also renown for such population peaks, at which time populations of Lemmus can become very transient and large-scale migrations occur. Conversely, at population troughs, densities are so low that the species can be very difficult to locate or are apparently absent from large regions. These large-scale migrations are the origin of the myth of hordes of lemmings committing suicide by throwing themselves from cliffs.

Many populations undergo localized extinctions and recolonizations, so dispersal is an important feature of vole and lemming social systems. Most species disperse as juveniles during the summer or autumn months as they get driven away by the female. Some species such as water voles have much more unusual systems of dispersal, which take place in the spring and involve reproductive over-wintered adults, including pregnant females. This can result in rapid recolonization by even a small number of animals.

Feeding ecology and diet

Most species of voles and lemmings are highly herbivorous. Many are foliage eaters and consequently consume

larges quantities of leaves in order to meet their energetic demands. Meadow voles that feed on the cellulose-rich foliage of grasses can eat as much as their own body weight each day. Their activity cycles often reflect a constant cycle of eating to fill the stomach, followed by several hours of rest and digestion before commencing the cycle of feeding again. Some species are much more cosmopolitan in their diet and redbacked voles feed on a variety of leaves, seeds, and insects.

High mountain voles (Dinaromys) and snow voles (Chionomys) make large food stores of dried foliage and stems. This

is cut and left to dry before being transported to burrows and rock crevices to provide food during the winter months when fresh foliage is scarce. Lemmings feed largely upon mosses and lichens, especially the wood lemming (Myopus schisticolor), which is almost totally reliant upon just one or two species of moss. Much of this feeding during the winter occurs under-neath the cover of snow.

The tree voles are highly arboreal and known to eat large quantities of pine needles, with which they also construct their arboreal nests. The fossorial mole voles consume a variety bulbs and tubers and, in some parts of their range, they can be so numerous as to be a pest of root crops. Among the most carnivorous of all the species is the muskrat that feeds on substantial amounts of aquatic crustaceans, bivalve mollusks, and small vertebrates.

Reproductive biology

Voles and lemmings are renown for their huge reproductive rates and populations can reproduce exceedingly quickly; consequently, many species occur at very high densities and are also very important for sustaining many predator populations. The density of many predators has been shown to reflect direct changes in the vole and lemming populations of an area. Meadow voles can exceptionally produce as many as 17 young in a single litter, although average litter size is normally much less. Often northern populations have a larger litter size than southern populations of the same species.

The young of all species are born blind and naked, although development is usually very rapid and weaning can occur as quickly as two weeks after birth. The young are often reproductive themselves before they are one month old.

Most species experience a receptive period within hours of giving birth (postpartum estrus), at which time they are mated and conceive, so females are routinely suckling young and pregnant with their next litter simultaneously.

The tree voles have a much slower reproductive process than that seen in other voles and lemmings. The gestation period is normally around 28 days, although it can be extended up to nearly 50 days if the female is suckling a previous litter. Litters of only one to three young are born and the young are routinely not weaned until around 30–35 days old.

One of the most amazing aspects of reproduction within the group is the genetic determination of sex seen in some lemming and vole species. The wood lemming produces three different genotypes of female, each of which produces different sex ratios of offspring. Some females produce the normal 1 male: 1 female ratio, while the other two genotypes produce either a 1 male: 3 female ratio or all-female litters, respectively.

Conservation status

While some species of voles and lemmings are undoubtedly among the most numerous of small mammals, there are others that are highly threatened. In 2002, the IUCN considered nine species to be threatened, including three, that are Critically Endangered (Microtus evoronensis, M. mujanensis, and Dicrostonyx vinogradovi). A further 26 species are considered Near Threatened or Conservation Dependent, so despite the high reproductive rate and extreme abundance of some species, a quarter of all the vole and lemming species are considered to be threatened or Near Threatened. Many local populations of other species are also declining, and a further 42 subspecies are listed by the IUCN.

Habitat loss is the key factor contributing to the decline of most voles and lemmings. The loss of natural steppe and prairie habitats to agriculture has affected many species, and some of the more specialized genera such as tree voles or water voles have also lost significant habitat to logging or wetland drainage and development. The water voles have also been significantly affected by the introduction of American mink (Mustela vison) to Europe. Some species such as the northern water vole (Arvicola terrestris) and root vole (Microtus oeconomus) have been the subject of successful conservation breeding and reintroduction programs carried out by zoos in Europe.

Significance to humans

Voles and lemmings are highly significant within their environments. Some species can be significant pests of agriculture, especially in the cyclic species when densities become very high during population peaks. They are pests of arable crops and also forestry and orchards by removing bark from the bases of trees or destroying the roots. The fossorial species also cause extensive damage to root crops. They can significantly affect stocking densities of grazing animals by directly competing for forage and damaging pastures. Some species are also important wild reservoirs of livestock or zoonotic diseases, uch as plague and tularaemia.

The muskrat is a very important fur-bearing species, widely hunted for its pelt, but also kept and farmed, which has resulted in the escape or release and establishment of the species in Europe, Asia, and South America. Several other species such as the mole voles, water voles, and collared lemmings are also locally hunted for their fur. Lemmings are important species of myth and legend among a number of indigenous peoples from northern latitudes.

Species accounts

List of Species

Muskrat

Ondatra zibethicus

taxonomy

Ondatra zibethicus (Linnaeus, 1766), eastern Canada. Sixteen subspecies have been recognized, although not all may be valid.

other common names

None known.

physical characteristics

Head and body length 15.5–24.5 in (40–62 cm); weight 1.1–4 lb (550–1,820 g). Upperparts are dark brown, underparts are light grayish brown.

distribution

United States and Canada; introduced to parts of Europe, Asia, and South America.

habitat

Always found around water, lakes, rivers marshes, and brackish lagoons.

behavior

Muskrats either dig burrows in the bank or build large floating lodges of vegetation. They are known to sometimes live as extended family groups.

feeding ecology and diet

Aquatic vegetation, invertebrates, and small vertebrates.

reproductive biology

Litters of 4–8 young are born after a gestation period of 25–30 days. As many as five or six litters a year may be produced.

conservation status

Not threatened; generally widespread and numerous. The status of the Rio Grande muskrat (O. zibethicus ripensis) is unclear and this subspecies may be threatened.

significance to humans

A very important fur-bearing species that is widely hunted and farmed. It has become a major pest in some regions where it has escaped or been released.

Northern water vole

Arvicola terrestris

taxonomy

Arvicola terrestris (Linnaeus, 1758), Uppsala, Sweden. As many as 40 subspecies have been recognized, although many are probably not valid.

other common names

None known.

physical characteristics

Head and body length 7–15 in (18–38 cm); weight 2.5–15.8 oz (70–450 g). Upperparts are light to dark brown, underparts are buffy to slate gray.

distribution

Northwestern and central Europe, and Asia.

habitat

Aquatic forms adjacent to rivers, lakes, marshes, and lagoons; the fossorial form occurs in dry pastures and occasionally woodland.

behavior

Two clear and very different ecological forms exist: a large aquatic form and a much smaller fossorial form. Almost all aspects of ecology differ between these two. The fossorial forms live at high density and are cyclic, while the aquatic populations occur at much lower densities and do not exhibit cycles.

feeding ecology and diet

Foliage, roots, and tubers.

reproductive biology

Litters of 4–8 young are produced after a gestation period of around 21 days. Weaning is very early at 14–18 days.

conservation status

The aquatic forms are declining and locally highly threatened, while the fossorial forms are often numerous pests. Captive breeding and reintroduction has occurred in threatened populations.

significance to humans

Hunted for fur across some parts of its range, can also be a pest to root crops and fruit trees.

Prairie vole

Microtus ochrogaster

taxonomy

Microtus ochrogaster (Wagner, 1842), Indiana, United States. Seven subspecies have been recognized.

other common names

None known.

physical characteristics

Head and body length 5–7 in (13–18 cm); weight 1–2 oz (35–50 g). Upperparts dark brown to black, underparts light tan.

distribution

United States across the central prairies and an isolated population in the coastal southeast.

habitat

Dry open grassland.

behavior

A very important prey species across the prairies. They occupy tunnel systems at or around ground level and are active day and night. Populations are cyclic every three or four years.

feeding ecology and diet

Foliage and roots.

reproductive biology

Monogamous. Litters of 2–4 young are born after a gestation period of around 21 days.

conservation status

Not generally considered threatened; in fact, it may be a very numerous species in many areas. The isolated population in Louisiana may be Extinct.

significance to humans

An important species for sustaining the prairie ecosystem.

Red tree vole

Arborimus longicaudus

taxonomy

Arborimus longicaudus (True, 1890), Oregon, United States. Two subspecies are recognized, one of which, A. longicaudus silvicola, is sometimes considered a separate, distinct species.

other common names

None known.

physical characteristics

Head and body length 6.5–8 in (16–20.5 cm); weight 1–2 oz (30–50 g). Upperparts reddish brown or cinnamon, underparts whitish to gray.

distribution

United States along the Pacific coast of Oregon.

habitat

Old coniferous forests.

behavior

Mainly nocturnal and arboreal. Living high up in trees and constructing large stick and needle nests in the branches.

feeding ecology and diet

Fir needles, predominantly Douglas fir (Pseudotsuga menziesii).

reproductive biology

Litters of 1–3 young are born after a gestation of around 28 days, although implantation is delayed if the female is already lactating with a previous litter.

conservation status

Not threatened yet, although populations are declining due to logging of their habitat.

significance to humans

None known.

Norway lemming

Lemmus lemmus

taxonomy

Lemmus lemmus (Linnaeus, 1758), Lappmark, Sweden. No subspecies are recognized.

other common names

None known.

physical characteristics

Head and body length 3–7 in (8–17.5 cm); weight 0.5–4.5 oz (20–130 g). Fur color is brown to black.

distribution

Scandinavia.

habitat

Open tundra and subarctic bogs.

behavior

Mainly nocturnal and populations are highly cyclic undergoing mass migrations in peak years; active year-round, often under-neath the cover of snow. Ecologically, a very important prey species in the tundra.

feeding ecology and diet

Mosses, lichens, bark, and some grasses.

reproductive biology

They have very fast reproductive rate and can produce litters of up to 13 young after only a 16-day gestation. Up to six litters can be produced during the summer.

conservation status

Not threatened.

significance to humans

A familiar animal of Scandinavian myths and legends.

Wood lemming

Myopus schisticolor

taxonomy

Myopus schisticolor (Lilljeborg, 1844), Gulbrandsdal, Norway. Five subspecies are recognized.

other common names

None known.

physical characteristics

Head and body length 3.5–5.5 in (9–13.5 cm); weight 0.5–1.5 oz (20–45 g). Upperparts are dark grayish black with a reddish brown area along the center back. Underparts are paler.

distribution

From Scandinavia across to the Pacific coast of Russia.

habitat

Old coniferous forests.

behavior

Mainly nocturnal, living in runs among deep forest litter and moss. Populations are known to be cyclic.

feeding ecology and diet

Mosses, lichens, and some grasses during the summer.

reproductive biology

Sex ratio is chromosomally manipulated; only around 25% of the population is male. Females occur of three different genotypes, one of which only gives birth to female offspring. Litters of up to six young are produced every 25 days.

conservation status

In 2002, considered by the IUCN to be Lower risk/Near Threatened.

significance to humans

None known.

Long-clawed mole vole

Prometheomys schaposchnikowi

taxonomy

Prometheomys schaposchnikowi Satunin, 1901, Caucasus Mountains, Georgia.

other common names

None known.

physical characteristics

Head and body length 6.5–8.5 in (17–22 cm); weigth 2–3 oz (50–80 g). Upperparts grayish brown, underparts pale gray. Cinnamon tint throughout.

distribution

Caucasus Mountains, in Georgia and Turkey.

habitat

Alpine and subalpine meadows.

behavior

A burrowing, subterranean rodent that throws up heaps of soil, rather like a mole rat. They live in small groups that share a common burrow system.

feeding ecology and diet

Stems, shoots, and roots.

reproductive biology

Two litters of approximately three young are born each year.

conservation status

Not threatened.

significance to humans

None known.

Silvery mountain vole

Alticola argentatus

taxonomy

Alticola argentatus Severtzov, 1879, Kazakhstan. Nine subspecies are recognized; the taxonomic status of several is unclear.

other common names

None known.

physical characteristics

Head and body length 4.5–7.5 in (12–19 cm); weight 0.7–1.9 oz (20–55 g). Upperparts gray or brown, underparts whitish.

distribution

Central Asia in the Tien Shan mountains.

habitat

Alpine scree slopes and other rocky areas.

behavior

Both nocturnal and diurnal. It builds large nests among rocks and is also active underneath snow cover during the winter.

feeding ecology and diet

Foliage, stems, seeds, and roots. They construct food stores of cut plants that they dry in the sun before caching for the winter months.

reproductive biology

Produces 2–3 litters of around five young a year. Reproductive output varies with altitude and higher productivity tends to occur in lower altitude populations.

conservation status

Not threatened.

significance to humans

None known.

Bank vole

Clethrionomys glareolus

taxonomy

Clethrionomys glareolus (Schreber, 1780), Denmark. At least 30 subspecies have been described, but the taxonomic status of many of these is uncertain.

other common names

None known.

physical characteristics

Head and body length 5–8 in (12.5–20 cm); weight 0.5–2 oz (15–50 g). Upperparts dark gray with reddish tint, underparts dark gray to white.

distribution

Western Europe, across Russia to north Asia.

habitat

Forest, scrub, parkland, gardens, and hedgerows.

behavior

Both nocturnal and diurnal, living in burrows and climbing in low vegetation. Populations in the north of its range are cyclic, while southern ones are more stable.

feeding ecology and diet

Seeds, fruit, buds, bark, and insects.

reproductive biology

Produces litters of 3–5 young following a gestation of 16–22 days. It will breed all year if conditions are favorable and tree seed is available.

conservation status

Not threatened.

significance to humans

None known.

Steppe lemming

Lagurus lagurus

taxonomy

Lagurus lagurus (Pallas, 1773), Kazakhstan.

other common names

None known.

physical characteristics

Head and body length 3.5–5.5 in (9–14 cm); weight 0.5–1 oz (10–25 g). Upperparts light gray to cinnamon gray, underparts whitish. Black stripe along spine.

distribution

Central Asian steppes from the Ukraine to China.

habitat

Open grassland steppe, semi-deserts, and cultivated fields.

behavior

Mainly nocturnal, but occasionally diurnal also. It lives in burrow systems that can join up to cover large areas. Populations fluctuate and they can be exceedingly numerous in some years.

feeding ecology and diet

Seeds, foliage, shoots, and roots.

reproductive biology

They can produce up to five litters of young each year, with as many as 12 young in a litter. Pregnancy lasts around 20 days and the young are reproductive by 30–45 days old.

conservation status

Not threatened.

significance to humans

A serious pest of crops and grazing pastures when populations are high.

Resources

Books

Carleton, M. D., and G. G. Musser. "Muroid Rodents." In Orders and Families of Recent Mammals of the World, edited by S. Anderson and J. K. Jones Jr. New York: John Wiley and Sons, 1984.

Corbett, G. B. The Mammals of the Palaearctic Region: A Taxonomic Review. London: British Museum (Natural History), 1978.

Mitchell-Jones, A. J., et al. The Atlas of European Mammals. London: Academic Press, 1999.

Nowak, R. M. Walkers Mammals of the World. 6th ed. Baltimore and London: Johns Hopkins University Press, 1999.

Wilson D. E., and S. Ruff, eds. The Smithsonian Book of North American Mammals. Washington, DC: Smithsonian Institute Press, 1999.

Mike J. R. Jordan, PhD