Tundra Voles have the northernmost distribution of any North American species of Microtus. They are widespread in northern latitudes in Eurasia, too, where they are known as Root Voles, and probably migrated to North America across the Bering land-bridge during the Pleistocene. They prefer moist meadow habitats, particularly near lakes, streams, and marshes. Tundra Voles are active year-round. In the fall, they store food—grass seeds and other plant materials—for winter. Many northern predators depend on this species, including weasels, Wolverines, Arctic Foxes, falcons, gulls, and owls.

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Mammal Species of the World

Microtus oeconomus is a Holarctic species, with a wide range extending from north-west Europe in the west to Alaska in the East. In North America, restricted to Alaska and northwest Canada. In Europe, its main range extends from eastern Germany and northern Fennoscandia through Poland, Belarus, and northern and central European Russia; isolated relict populations are found in the Netherlands, southern Norway and northern Sweden, the Finnish coast, and Austria, Slovakia and Hungary (van Apeldoorn 1999, Shenbrot and Krasnov 2005). In China found in northern Xinjiang and northern Nei Mongol. In Mongolia found in northern areas including Mongol Altai, Hangai, Hövsgöl Hentii and Ikh Hyangan mountain ranges, and Mongol Daguur Steppe (Sokolov et al., 1985).

Microtus oeconomus (pronounced e-KON-uh-mus), commonly known as the tundra or root vole, is one of only four Holarctic rodents and the only species of Microtus that is found on all northern continents. In the Nearctic, it is found from the extreme northern edge of British Columbia northward to the Arctic coast, and from western Northwest Territories, through Yukon Territory and nearly all of Alaska. It has the northernmost distribution of any Microtus species in North America, with occurrences to around 71°N in Alaska. In the Palearctic, tundra voles occupy a somewhat broader range, extending from Scandinavia and the Netherlands in the west, throughout northern Europe and Asia to Siberia in the east, and south as far as Mongolia.

Biogeographic Regions: nearctic (Native ); palearctic (Native )

Other Geographic Terms: holarctic

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Tundra and taiga of Holarctic; Scandinavia and the Netherlands to borderlands of Bering Sea, including Sakhalin and Kurile islands, and south to eastern Germany, Ukraine, southern Kazakhstan, Mongolia, and the Ussuri region; St. Lawrence Island in the Bering Sea; Alaska through Yukon Territory to western Northwest Territories and extreme northwestern British Columbia (Musser and Carleton, in Wilson and Reeder 1993).

Microtus oeconomus is a medium-sized vole and varies in color dorsally from darker brown or grayish to lighter shades of cinnamon, rusty brown, or ocher. All color variations display a mixture of black-tipped hairs in the dorsal pelage. Sides are somewhat paler and the ventral surface is much lighter, from buff or ash gray to white. The tail is slightly to strongly dichromatic, being darker above and paler below. There is a fair amount of color variation in the species, which can often be related to habitat and geography. Tundra voles are generally lighter colored in more open habitats, and have yellow or grayish tones in tundra or forested habitats, respectfully.

Tundra voles display sexual size dimorphism, with adult males roughly 30% larger than females. The size and weight of the species is also variable relative to latitude and geography, especially so in the Palearctic. Individuals in populations at higher latitudes are generally larger and have proportionally smaller tails as a possible adaptation to colder temperatures. In addition, insular subspecies are generally larger than continental counterparts. Weight ranges from 25 to 80 g, with an average around 50 g. Total length ranges from 118 mm in the Old World, to 226 mm in the larger subspecies found in the New World. The tail is relatively short, generally being less than 30% of the total length. The name Microtus means “small ear” and refers to the short ears hidden in pelage that are a characteristic common to members of the genus. The dental formula for M. oeconomus follows the basic pattern for all Microtus: incisors 1/1, canines 0/0, premolars 0/0, molars 3/3.

Microtus oeconomus maintains a relatively high basal metabolic rate (compared to most rodents) of 12.5 mL O2 per gram of body mass per hour. This is due primarily to the high thermoregulatory demands of small endothermic mammals in cold environments.

Range mass: 25 to 80 g.

Average mass: 50 g.

Range length: 118 to 226 mm.

Average basal metabolic rate: 12.5 cm^3 oxygen/hour.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

Average basal metabolic rate: 0.566 W.

Length: 23 cm

Weight: 80 grams

Length:
Range: 152-225 mm

Weight:
Range: 25-80 g

Type for Microtus oeconomus
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Sex/Stage: Female; Adult
Preparation: Skull; Remainder in Fluid
Collector(s): J. Dawson
Year Collected: 1865
Locality: Plover Bay, Bering Strait, Chukotskiy, Russia, Asia

Habitat and Ecology

Systems

• Terrestrial

Microtus oeconomus inhabits the tundra and taiga biomes and prefers mesic sedge meadows with abundant cover. It is commonly found along the edges of lakes and streams where this and similar habitats occur. Although this habitat usually occurs in relative lowlands, tundra voles are also found in wetter areas of mountainous regions at elevations of up to 2,500 meters. In the Palearctic, M. oeconomus is found in a broader range of habitats, commonly inhabiting mixed forest, taiga, and forest-steppe biomes with similar conditions. Habitat is most strongly selected on the basis of food quality and amount of cover provided.

Range elevation: 0 to 2,500 m.

Habitat Regions: temperate ; polar

Terrestrial Biomes: tundra ; taiga ; forest ; mountains

Wetlands: bog

Comments: Moist to wet tundra; tundra areas around streams, lakes, marshes; muskeg, among logs and roots of conifers. Sometimes in thick grass in drier areas. Makes shallow burrows and runways through vegetation. May use frost cracks as extensions of runway system. Nests are in shallow burrows or under debris.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Tundra voles are strictly vegetarian and preferentially feed on sedges (Carex sp. and Eupharium sp.) that grow in their favored habitat of wet, marshy tundra. Sedges make up around 70 to 80% of their diet, with the remainder comprising herbs, mosses, lichen, and small woody shrubs. These percentages vary seasonally, and a 30% decrease in sedge consumption is common in winter, with mosses and lichens becoming a relatively major component of the diet. Other plant foods that are preferred when available include Equisetum sp., Dryas integrifolia, Salix sp. and various grasses.

In the fall, Microtus oeconomus creates large caches of stored seeds and rhizomes to supplement its winter diet. Native peoples of North America occasionally sought out these caches in order to obtain large quantities of desired foods, such as licorice root.

Plant Foods: leaves; roots and tubers; wood, bark, or stems; bryophytes; lichens

Foraging Behavior: stores or caches food

Primary Diet: herbivore (Folivore )

Comments: Eats mainly green grasses and sedges in summer. Stores rhizomes (especially knotweed and licorice root) and grass seeds for later use (Whitaker 1980).

Populations of Microtus oeconomus experience cyclical fluctuations, reaching peak densities of 70 to 80 voles per hectare. As explained above, during these peak density years, tundra voles provide a large food base for many predator species. When present in such large numbers, they can also significantly alter the biological production of the tundra ecosystem through their foraging activities. Tundra voles share their habitat preferences with several similar species (e.g., M. longicaudus, M. pennsylvanicus, M. agrestis and M. xanthognathus) but generally either avoid competition through niche specialization, or out-compete the other species, as in the case of M. agrestis.

Tundra voles are host to a variety of internal and external parasites. Endoparasites include cestodes (Echinococcus sp., Paranoplocephala sp., and Taenia sp.), nematodes (Heligmosomoides sp.), and trematodes (Quinqueserialis nassalli). Ectoparasites include fleas (Siphonaptera sp.), lice (Polyplax sp.), and ticks (Ixodes angustus).

Commensal/Parasitic Species:

• cestodes (Echinococcus, Paranoplocephala, and Taenia)
• nematodes (Heligmosomoides)
• trematodes (Quinqueserialis nassalli)
• fleas (Siphonaptera)
• lice (Polyplax)
• ticks (Ixodes angustus)

Microtus oeconomus is an important prey source for many carnivores. During cycles of peak density, they have been known to comprise the majority of the diet for species such as the arctic fox (Vulpes lagopus) in Alaska. Other known terrestrial predators of M. oeconomus include weasels, martens, red foxes, and wolverines. In addition, numerous avian species prey on tundra voles, including owls, falcons, hawks, jaegers, gulls, and shrikes.

Known Predators:

• weasels (Mustela)
• martens (Martes)
• red foxes (Vulpes vulpes)
• arctic foxes (Vulpes lagopus)
• wolverines (Gulo gulo)
• owls (Strigiformes)
• falcons (Falco)
• hawks (Accipitridae)
• jaegers (Stercorarius)
• gulls (Larus)
• shrikes (Laniidae)

Anti-predator Adaptations: cryptic

Populations may fluctuate, with periodically high densities. Density generally in the range of 4-50/ha. Summer home ranges of sexually active adult males do not overlap, average about 3900 sq m; home ranges of females (average about 1100 sq m) generally overlap with each other and with home range of one adult male (Lambin et al. 1992).

Olfaction is presumably the most important and well-developed sense in Microtus oeconomus. Scents are commonly used by the species to identify familiar or unfamiliar individuals and to determine their age, sex, reproductive condition, diet, or social status. Conspicuous hip and preputial glands used for scent production are located on both sexes of adult tundra voles. The glands are largest in males and older individuals, and are only present in females at higher latitudes. Scent marking behaviors such as scratching or rubbing are also displayed by M. oeconomus. Hearing is well-developed in tundra voles and they may occasionally use vocalizations for communication, although little is known about this behavior.

Communication Channels: acoustic ; chemical

Other Communication Modes: scent marks

Perception Channels: visual ; acoustic

There is insufficient research on Microtus oeconomus for a definitive lifespan to be established. However, relatively few adults survive much longer than one year in the wild, and the maximum age for other species of Microtus is commonly around two years.

Range lifespan

Status: wild: 2 (high) years.

Typical lifespan

Status: wild: 1 (high) years.

Average lifespan

Status: captivity: 1.8 years.

Observations: Voles, in general, are short-lived and show seasonal population crashes, probably due to lack of food. These animals are estimated to live up to 1.8 years (Bernhard Grzimek 1990), but without further studies their maximum longevity cannot be determined.

Various mating systems have been observed in Microtus oeconomus, including promiscuous, multi-partner groups, polygyny, and monogamy. The mating system adopted is determined primarily by the general spacing patterns of a specific population, which are in turn influenced by factors such as habitat, season, and population densities (discussed below). In general, a slightly biased female (57%) to male (43%) ratio favors a system of polygyny in tundra voles. Accordingly, single-male polygyny and multi-male promiscuity are the most common systems observed during normal breeding season. However, facultative monogamy is adopted in isolated territories or patchy habitats with low densities and can be relatively long-lasting.

Mating System: monogamous ; polygynous ; polygynandrous (promiscuous)

Female tundra voles are polyestrous and often produce two to three litters per year. The breeding season generally lasts from late April to September during years with peak densities, and is around one to two months shorter in years of low densities. Winter breeding has been observed very rarely, and is attributed to unusually warm summers resulting in late fall re-growth.

Litter sizes of Microtus oeconomus are relatively large for the genus and usually range from four to eight offspring, with an average of 6.9. Litter size increases with age of the female, and over-wintered females are usually much more productive than spring-born females. Litters produced by northern populations of tundra voles are more female biased than those of southern populations. This bias is thought to be influenced by several factors both before and after birth, but this is not well understood. The gestation period for M. oeconomus lasts 20 to 21 days. Neonates weigh about 3 g at birth, have no external hair (except vibrissae), and are essentially poikilothermic. The newborns are very altricial and depend heavily on the mother during development. After five days the young are covered in hair and their eyes open 11 to 13 days after birth. They develop quickly and are weaned after 18 days, at which point they are fairly independent. Maximum size is reached as early as two months after weaning. Sexual maturation is reached in three weeks by females, whereas males do not usually mature until six to eight weeks. This sex-based delay in maturation serves as a defense against inbreeding in that females are almost always fertilized before their male siblings are able to mate.

Breeding interval: Female tundra voles breed several times in a year.

Breeding season: Breeding generally occurs from April to September. Very rarely, winter breeding has been observed

Range number of offspring: 4 to 8.

Average number of offspring: 6.9.

Range gestation period: 20 to 21 days.

Average weaning age: 18 days.

Average time to independence: 18 days.

Average age at sexual or reproductive maturity (female): 3 weeks.

Range age at sexual or reproductive maturity (male): 6 to 8 weeks.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous

Average birth mass: 2.43 g.

Average number of offspring: 7.

Average age at sexual or reproductive maturity (female)

Sex: female: 30 days.

Females provide the greater investment in the offspring, including nest construction, protection, and care of the young. However, increases in paternal investment in southern populations of tundra voles have been observed. It has been suggested that this is a result of longer foraging times required by southern females during lactation due to increased resource limitation at lower latitudes.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)

Females containing 3-11 embryos have been reported (Burt and Grossenheider 1976). Mating system probably is polygynous (Lambin et al. 1992).

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Species: 73
Species With Barcodes: 1

Overall, Microtus oeconomus is a relatively stable species and not currently listed as threatened or endangered on any listing. It is also categorized by the IUCN as a species of “least concern”. However, insufficient knowledge of several isolated subspecies has resulted in their categorization of “data deficient” by the IUCN. These subspecies include M. o. amakensis, M. o. elymocetes, M. o. innuitus, M. o. popofensis, M. o. punukensis, and M. o. sitkensis. Furthermore, two subspecies, M. o. mehelyi and M. o. arenicola, are categorized by the IUCN as “vulnerable” and “critically endangered”, respectively. Population declines in some subspecies have been attributed to habitat deterioration. In the case of M. o. arenicola, competition with M. arvalis has additionally contributed to population declines on some islands.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Major Threats

Conservation Actions

Tundra voles are known carriers of several diseases. Of most importance to humans is the role of Microtus oeconomus as a carrier of the bacterium (Francisella tularensis) that causes tularemia in humans. This disease is transmitted by direct contact and is fatal in about 7% of untreated human cases. Additionally, at peak densities they can compete with livestock for forage and cause damage to trees by gnawing on the roots.

Negative Impacts: injures humans (carries human disease)

Microtus oeconomus is commonly considered an ideal species for scientific research due to its adaptability to laboratory settings, quick development, and rapid population growth. Many important hypotheses have been tested using tundra voles as model species. As discussed above, tundra voles also provide an important food base for many carnivores (such as mink and foxes) that are highly valued for their fur.

Positive Impacts: research and education

Comments: Lance and Cook (1998) examined the biogeographic history of this species in Beringia and the southern coast of Alaska, based on allozymic, chromosomal, and morphologic variation. See Musser and Carleton (in Wilson and Reeder 2005) for extensive taxonomic discussion.

Microtus ratticeps or M. kamtschaticus have been proposed to be proper name for this species, but Baker et al. (2003), Musser and Carleton (in Wilson and Reeder 1993, 2005), and other authors have continued to use M. oeconomus; the nomenclatural uncertainty needs formal resolution (Musser and Carleton).