| Creeping vole | |
|---|---|
 | |
| Microtus oregoni photographed atWind River Experimental Forest | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Rodentia |
| Family: | Cricetidae |
| Subfamily: | Arvicolinae |
| Genus: | Microtus |
| Subgenus: | Pitymys |
| Species: | M. oregoni |
| Binomial name | |
| Microtus oregoni (Bachman, 1839) | |
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| Distribution of the creeping vole | |
| Synonyms[3] | |
List
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Thecreeping vole (Microtus oregoni), sometimes known as theOregon meadow mouse, is a smallrodent in the familyCricetidae. Ranging across thePacific Northwest of North America, it is found inforests,grasslands,woodlands, andchaparral environments. The small-tailed, furry, brownish-graymammal was first described in the scientific literature in 1839, from a specimen collected near the mouth of theColumbia River. The smallest vole in its range, it weighs around 19 g (11⁄16 oz). At birth, they weigh1.6 g (1⁄16 oz), are naked, pink, unable to open their eyes, and the ear flaps completely cover the ear openings. Although not always common throughout their range, there are no major concerns for their survival as a species.
The animal was described in 1839 byJohn Bachman.[4] The original scientific name wasArvicola oregoni with a common name of the Oregon meadow mouse.[4] Thetype specimen was an older male collected November 2, 1836 near the mouth of theColumbia River in Oregon.[4] The specimen had been submitted to Bachman for review byJohn Kirk Townsend.[4] Subsequent authorities state that it was collected atAstoria, Oregon, which is at the mouth of the Columbia River.[5] In 1857, Baird placedArvicola oregoni in a section Chilotus of the subgenusArvicola of the genusArvicola.[6] In 1874, PNAS paper, Coues reclassified Chilotus as a subgenus and refers to the animal asArvicola (Chilotus) oregonus.[7][8] Miller subsequently reclassified the animal in the genusMicrotus and maintained the subgenusChilotus.[9] This was the first reference to the animal under its current scientific nameMicrotus oregoni.[5] It was subsequently reclassified to the subgenusMynomes,[3] though theAmerican Society of Mammalogists lumps that subgenus's species in with subgenusPitymys.[10]
| Skull dimensions[5] | ||
|---|---|---|
| Minimum | Maximum | |
| Basal length | 20.9 mm (0.82 in) | 23.4 mm (0.92 in) |
| Nasal length | 6.7 mm (0.26 in) | 7.3 mm (0.29 in) |
| Zygomatic breadth | 14 mm (0.55 in) | 14.9 mm (0.59 in) |
| Mastoid breadth | 11 mm (0.43 in) | 12.6 mm (0.50 in) |
| Upper molar alveolus | 5.5 mm (0.22 in) | 6.1 mm (0.24 in) |
On average, creeping voles weigh around19 g (11⁄16 oz) with a reported range of14.5 to 27.5 g (1⁄2 to 1 oz)[5] The average length is around 140 mm (5.5 in), with a range of around 129 to 154 mm (5.1 to 6.1 in)[5] Compared to other voles within their geographic range, they are the smallest.[5] They have smaller eye opening (around 2 mm (0.079 in) in diameter) compared to other voles that share the same geographic range (sympatric) or have adjacent ranges (parapatric).[5] There are other distinguishing features of the roots and enamel of themolar teeth that help in differentiation.[5] Unlike other voles in the range, only the creeping vole and the (much larger) water vole have five plantar tubercles on the hindfeet.[5]
They arePentadactyl, although thepollex is reduced in size and lack a claw.[5] They walk with their feet planted firmly on the ground (plantigrade locomotion).[5] The foot pads have a moderate amount of fur.[5]
The fur markings are plumbeous to a dark brown or black.[5] There are sometimes yellowish hair markings as well.[5] The underside fur markings tend to be lighter beige to whitish.[5] The tail may be gray to black and often lighter below.[5]
Creeping voles have a relatively short tail, measuring less than 30% their total body length.[5] They have short ears, which are nearly hairless, though a few black hairs present.[5] They protrude just slightly from the fur around the head.[5] They have eightmammae, with two pairs present in each of the pectoral and inguinal regions.[5]
The skull of the creeping vole has a low, flat profile, with a long and slender snout.[5] Thezygomatic arches are somewhat delicate.[5] Theincisive foramen is short and wide, but not so much as to be a distinguishing feature.[5] They have small molars.[5]
Creeping voles are found inBritish Columbia inCanada and inWashington,Oregon andnorthern California, in theUnited States.[1] They are found as far north asPort Moody, British Columbia and as far south asMendocino City, California.[5] The western range in Washington extends east toMount Aix,Lake Chelan, and Signal Peak.[5] The range in Oregon extends east to the north base ofThree Sisters and toCrater Lake.[5] There are variable reports as to their occurrence in theWillamette Valley of Oregon.[5] In California, they are found as far east asBeswick andSouth Yolla Bolly Mountain.[5]
They are found in coniferous forests and woodlands, grasslands, and chaparral.[2] They are found at sea level through altitudes of nearly 2,400 m (7,900 ft).[5] They are more populous in areas of disturbance thanvirgin forests.[2] They are burrowing animals and will also use fallen logs, other debris, and patches of grass for cover.[2] The burrows are shallow.[2] They are found inmoist forests along the coast, but may do well in drier areas.[2]
It is suspected that ancestral voles migrated from Eurasia 1.2 million years ago.[5] However, noPleistocene-era fossils of creeping voles have been identified.[5]
Creeping voles establish nests of dry grass in protected areas, such as under logs.[1] The breeding season varies by latitude, but is mainly March to September in Oregon and British Columbia.[1] Gestation lasts around 23 days. Each litter bears three to four young and the females may produce four or five litters a year.[1] The naked, pink newborn young weigh around1.6 g (1⁄16 oz).[11] Their eyes are closed and skin flaps cover the ear openings.[11]
Creeping voles are primarily nocturnal, though they are sometimes active during the day.[1] They are herbivorous, probably eatingforbs and grasses, as well asfungi.[1]
Creeping vole females have XO sex chromosomes, while males have XY. Evolutionary geneticists have investigated these sex chromosomal features of creeping voles. A models for the evolution of creeping vole sex chromosomes was published by researchers from the University of Edinburgh in 2001.[12] Recently, it was discovered the Y chromosome has been lost, the male-determining chromosome is a second X that is largely homologous to the female X, and both the maternally inherited and male-specific sex chromosomes carry vestiges of the ancestral Y. This is quite unusual in mammals, as the XY system is fairly stable across a number of mammal species.[13]
Although it is not widely distributed and not always common, the creeping vole is listed as "Least Concern" by the IUCN Red List.[1] The justifications for the listing are the lack of major threats, the stability of populations, and the adaptability of the animal to environmental changes.[1] Treatment of Douglas-fir plantations with herbicides in British Columbia did not affect creeping vole populations.[1] No conservation concerns are raised, since there are thought to be sufficient areas of protected habitat within its range.[1]NatureServe lists the species as secure within its range.[2]
Footnotes:
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