Species accounts

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.

Lemmus Lemmus

H Lagurus lagurus H Lemmus lemmus H Ondatra zibethicus

H Arvicola terrestris H Prometheomys schaposchnikowi

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 Populations

H Clethrionomys glareolus H Arborimus longicaudus H Microtus ochrogaster

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 underneath 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.

Alticola Argentatus

H Alticola argentatus H Myopus schisticolor

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. ♦

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