Creeping vole

The animal was described in 1839 by John Bachman.^[4] The original scientific name was Arvicola oregoni with a common name of the Oregon meadow mouse.^[4] The type specimen was an older male collected November 2, 1836 near the mouth of the Columbia River in Oregon.^[4] The specimen had been submitted to Bachman for review by John Kirk Townsend.^[4] Subsequent authorities state that it was collected at Astoria, Oregon, which is at the mouth of the Columbia River.^[5] In 1857, Baird placed Arvicola oregoni in a section Chilotus of the subgenus Arvicola of the genus Arvicola.^[6] In 1874, PNAS paper, Coues reclassified Chilotus as a subgenus and refers to the animal as Arvicola (Chilotus) oregonus.^[7][8] Miller subsequently reclassified the animal in the genus Microtus and maintained the subgenus Chilotus.^[9] This was the first reference to the animal under its current scientific name Microtus oregoni.^[5] It was subsequently reclassified to the subgenus Mynomes,^[3] though the American Society of Mammalogists lumps that subgenus's species in with subgenus Pitymys.^[10]

 

On average, creeping voles weigh around 19 g (11⁄16 oz) with a reported range of 14.5 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 the molar 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 are Pentadactyl, although the pollex 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 eight mammae, 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] The zygomatic arches are somewhat delicate.^[5] The incisive 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 in British Columbia in Canada and in Washington, Oregon and northern California, in the United States.^[1] They are found as far north as Port Moody, British Columbia and as far south as Mendocino City, California.^[5] The western range in Washington extends east to Mount Aix, Lake Chelan, and Signal Peak.^[5] The range in Oregon extends east to the north base of Three Sisters and to Crater Lake.^[5] There are variable reports as to their occurrence in the Willamette Valley of Oregon.^[5] In California, they are found as far east as Beswick and South 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 than virgin 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 in moist 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, no Pleistocene-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 around 1.6 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 eating forbs and grasses, as well as fungi.^[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]