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

Muridae Evolution

Distribution

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

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 Microti-nae 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 pat-

Lemmings Digestive System
A northern collared lemming (Dicrostonyx groenlandicus) in winter pelage showing elongated claws for digging in the snow. (Photo by Tom McHugh/Photo Researchers, Inc. Reproduced by permission.)

terned 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 (Clethri-onomys) 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 (Mi-crotus) 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.

Southern Bog Lemming
A meadow vole (Microtus pennsylvanicus) eating strawberries. (Photo by Dwight R. Kuhn. Bruce Coleman, Inc. Reproduced by permission.)
Meadow Bog Grasses
A northern bog lemming (Synaptomys borealis) in tall grass. (Photo by Gary Meszaros/Photo Researchers, Inc. Reproduced by premission.)

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 (Mi-crotus 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 scha-poschnikowi) 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 re-colonizations, 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

Collared Lemming Summer

A northern collared lemming (Dicrostonyx groenlandicus) in defensive position, claws ready to scratch. (Photo by Tom McHugh/Photo Re- A Norway lemming (Lemmus lemmus) foraging in the grass. (Photo by searchers, Inc. Reproduced by permission.) Tom McHugh/Photo Researchers, Inc. Reproduced by permission.)

A northern collared lemming (Dicrostonyx groenlandicus) in defensive position, claws ready to scratch. (Photo by Tom McHugh/Photo Re- A Norway lemming (Lemmus lemmus) foraging in the grass. (Photo by searchers, Inc. Reproduced by permission.) Tom McHugh/Photo Researchers, Inc. Reproduced by permission.)

Norway Rat Burrow
A field vole (Microtus agrestis) eats grass in its burrow. (Photo by Ernest A. Janes. Bruce Coleman, Inc. Reproduced by permission.)

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 red-backed voles feed on a variety of leaves, seeds, and insects.

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

Mouse Eating Seeds Underground
The bank vole (Clethrionomys glareolus) harvests seeds, berries, and nuts and stores them in underground caches. (Photo by Ernest A. Janes. Bruce Coleman, Inc. Reproduced by permission.)

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 underneath 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.

Brown Lemming
A brown lemming (Lemmus sibiricus) in sedge. (Photo by Tom McHugh/Photo Researchers, Inc. Reproduced by permission.)
Weaned Vole

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. mujanen-sis, 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 agricul ture, 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.

Lemmus Sibiricus

1. Northern water vole (Arvicola terrestris); 2. Norway lemming (Lemmus lemmus); 3. Red tree vole (Arborimus longicaudus); 4. Muskrat (Ondatra zibethicus); 5. Prairie vole (Microtus ochrogaster). (Illustration by Brian Cressman)

Steppe Lemmings

1. Silvery mountain vole (Alticola argentatus); 2. Steppe lemming (Lagurus lagurus); 3. Wood lemming (Myopus schisticoloi); 4. Bank vole (Clethri-onomys glareolus); 5. Long-clawed mole vole (Prometheomys schaposchnikowi). (Illustration by Brian Cressman)

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Responses

  • emppu riihij
    How long is the digestive system in meters?
    6 years ago
  • DOREEN
    How much do snow voles weigh lbs?
    6 years ago
  • ali yusef
    Are lemmings bigger than mice?
    4 years ago

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