Gray-tailed vole

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Gray-tailed vole
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Subfamily: Arvicolinae
Genus: Microtus
Subgenus: Mynomes
Species: M. canicaudus
Binomial name
Microtus canicaudus
Miller, 1897
See text.
Distribution of the gray-tailed vole

The gray-tailed vole, Microtus canicaudus, also known as the gray-tailed meadow vole and the gray-tailed meadow mouse, is a rodent in the genus Microtus, which are small eared "meadow voles" of the family Cricetidae. First collected in 1895, it is endemic to the Willamette Valley, Oregon and Clark County, Washington in the Pacific Northwest region of North America. Voles are small mammals and the gray-tailed vole is considered medium sized among voles. Historically, they were found among the prairies of the valley. They remain common, while much of these areas have been converted for agricultural purposes. For unclear reasons, populations densities of voles in an area may widely fluctuate from season to season and year to year. They are preyed upon by owls, hawks, and carnivorous mammals. Parasites include fleas and ticks. They build underground burrows and complex tunnel networks, sometimes shared with other burrowing animals in their area. Relatively little is known about their behavior in the wild, because they are elusive and unlikely to enter traps. Much of what is known about their behavior derives from laboratory studies.

Taxonomy[edit]

The scientific name of the gray-tailed vole is 'Microtus canicaudus. The generic name, Microtus, derives from the Greek words μικρός meaning "small" + οὖς "ear."[2] In Latin, the species name canicaudus derives from canens meaning "gray" and cauda meaning "tail."[2] The gray-tailed vole was first described in 1897 in the Proceedings of the Biological Society of Washington by Gerrit S. Miller.[3] The type specimen was collected in McCoy, Oregon on December 1, 1895 by B.J. Bretherton.[3][4] Miller's initial examination included the type specimen and eleven others.[3] Two from his collection had been obtained in Beaverton.[3] The remaining specimens, collected in McCoy, were part of the US National Museum Biological Survey, under C. Hart Merriam.[3] The gray-tailed voles is monotypic across its geographic range.[5] However, there are some variances described between specimens obtained on either side of the Columbia River.[5] They appear to be sibling species to the Montane vole (Microtus montanus) or to Townsend's vole (Microtus townsendii).[6]

The vole was classified as a geographic race or subspecies of the Montane vole by Hall and Kelson in 1951.[4][6] Laboratory analyses including electrophoresis and karyotype evaluations subsequently confirmed that they are two separate species.[1] The karyotypes of the Montane vole and the gray-tailed vole are dissimilar in terms of homology in 6 of 22 autosomal arms.[4] The quantity and distribution of heterochromatin among both X chromosomes and autosome is different as well.[4] The two species are allopatric, but not contiguously so.[7]

Description[edit]

Illustration of a related Microtus species

The gray-tailed vole is a medium sized vole, which are small mammals.[4] The pelage, or fur, on the back is yellowish-brown or yellowish-gray.[4] They have a short tail, which is black or brown above and more grayish below.[4] The pelage of the young is gray on the underside, with a darker "sooty" gray on the back.[8] The feet of the young are dusky and they have a gray tail, with a black stripe.[8] They are similar in size and overall appearance to the Montane vole.[9] However, the pelage has a more yellowish coloring and the tail is grayer than that of the Montane vole.[9] The type specimen measured 135 mm (5.3 in)in total length.[10] The tail vertebrae measured 33 mm (1.3 in) and the hind foot measured 20 mm (0.79 in).[10] Average typical adults are 141 mm (5.6 in) in total length, with a 35 mm (1.4 in) long tail.[9] The feet measure 20 mm (0.79 in) and the ears 12 mm (0.47 in).[9] They have an upper and lower incisor, and three upper and lower molars on each side, for a total of 16 teeth.[11]

Gray-tailed voles are sympatric with Townsend's vole (Microtus townsendii) and they share many similarities.[4] They can be distinguished based on appearance, because Townsend's vole has darker colorings, a relatively longer tail, and differences in the structure of the bony palate.[4] In comparison with the Montane vole, gray-tailed voles also differ in some aspects of the hard palate structure, more specifically, the incisive foramina.[4] It also shares its geographic range with the creeping vole (Microtus oregoni).[4] The gray-tailed vole has a sturdier build, larger eyes, and some differences in the upper molars[4]

Distribution and habitat[edit]

Prairie land in the Willamette Valley, now plowed over for agricultural use
Prairie in the Willamette Valley, converted for agricultural use.

The gray-tailed vole is endemic to the Willamette Valley, Oregon and Clark County, Washington.[4] The geographic range within the state of Oregon extends from Scappoose, Oregon and Gresham in the north, south through the Willamette Valley, to around Eugene.[4] Reports of the species east of the Cascades have been called into question.[4] Gray-tailed voles are prevalent in agricultural areas. They are found in and around pastures, hayfields, grain fields, and disturbed habitats.[4]

They previously inhabited grassy prairies of the valley.[12] These prairies had been annually burned by Native Americans.[5]

Range of gray-tailed vole and dwarf meadow mice in Oregon

In 1901, Edmund Heller visited McCoy, where the type specimen of the gray-tailed vole had been collected.[13] The account of his journey is relayed by Daniel Giraud Elliot.[13] Heller described the area around McCoy as "much the same kind of country as Beaverton, but more level and forested. The coast range is about fifteen miles distant. In some places, forests of Douglas fir occur, but the land is chiefly open and grassy. White oaks and a few yellow pine occur also, and the region I should judge was more Transition than that at Beaverton."[13] Heller had described Beaverton as "low and rolling, but hills are entirely lacking in the immediate vicinity of the town. The timbered land is covered with forests of yellow pine (Pinus jeffreyi), Douglas fir (Pseudotsuga taxifolia), white oak (Quercus zarryana), etc. The soil is chiefly black adobe except on the higher parts, where it is largely clay. The region evidently is Transition in character of its vegetation as shown by the presence of the yellow pine and white oak."[13]

In Mammals and Life Zones of Oregon, Vernon Orlando Bailey describes the Willamette Valley as part of the humid division of the Transition Zone.[14] Annual precipitation in the valley is 40 in (100 cm), with most falling in the winter.[14] The Willamette Valley is warmer and drier than the surrounding hills, less heavily forested, and better suited for agricultural use.[14] Mammals sharing the Transition Zone with the gray-tailed vole include: Roosevelt's elk, Columbian black-tailed deer, Oregon white-tailed deer, Washington rabbit, Oregon brush rabbit, silver gray squirrel, Douglas's squirrel, Townsend's chipmunk, Douglas's ground squirrel, Oregon flying squirrel, dusky wood rat, ruddy deer mouse, California red-backed mouse, red tree vole, white-footed phenacomys, Townsend's vole, Oregon creeping mouse, mountain beaver (Aplodontia rufa), jumping mice including Zapus princeps and Zapus trinotatus, Camas pocket gopher, Mazama pocket gopher, and northwest coast bobcat (Lynx rufus fasciatus).[14] Birds in the range include: Sooty grouse, Oregon ruffed grouse, band-tailed pigeon, California pygmv owl, Harris's woodpecker, northern pileated woodpecker, Lewis s woodpecker, Vaux's swift, Steller's jay, Townsend's warbler, western winter wren, California creeper, Oregon chickadee, chestnut-backed chickadee, wren tit, western golden-crowned kinglet, and black-headed grosbeak.[14]

Behavior[edit]

Gray-tailed voles are burrowing rodents.[1][15] They construct complex networks of tunnels and burrows.[1] They may also nest above ground, sheltered under wood, abandoned equipment, or other agricultural debris.[1] They are known to use the tunnel networks of the Camas pocket gopher.[15] The tunnels are built to provide shelter during wet periods, which are frequent throughout their range.[16] The burrows are interspersed with air trapped chambers.[16] In the event of tunnels flooding, they will swim to dry areas or chambers in the tunnel network.[15] If the networks completely flood, they will head for higher ground.[15][16] As many as 20-30 voles have been seen gathered on dry fence posts in flooded areas. When approached, the voles swam to safer ground nearby.[16] Where tunnels intersect, they sometimes establish middens. These may range in size from 8–15 cm (3.1–5.9 in) long by 3–5 cm (1.2–2.0 in) wide by 8–10 cm (3.1–3.9 in) deep.[16]

Gray-tailed voles are difficult to capture live in the wild.[2] They are unlikely to enter enclosure type live animal traps.[2] The most effective traps are laid inconspicuously along commonly used runways, such that the voles run directly into them.[2] Much of what is known about the voles has been obtained from observing them in captivity.[2]

Ecology[edit]

Growth and development of gray-tailed voles[16]
Male Female
Age (weeks) Weight Length Weight Length
1 6.0 g (0.21 oz) 68.7 mm (2.70 in) 5.5 g (0.19 oz) 66 mm (2.6 in)
2 11 g (0.39 oz) 97.5 mm (3.84 in) 10.3 g (0.36 oz) 92.2 mm (3.63 in)
3 16.5 g (0.58 oz) 117 mm (4.6 in) 15.2 g (0.54 oz) 114.8 mm (4.52 in)
4 21.0 g (0.74 oz) 129.5 mm (5.10 in) 19.3 g (0.68 oz) 24 mm (0.94 in)
5 24.6 g (0.87 oz) 136.9 mm (5.39 in) 21.3 g (0.75 oz) 129 mm (5.1 in)
6 26.1 g (0.92 oz) 140.9 mm (5.55 in) 22.2 g (0.78 oz) 131.1 mm (5.16 in)
7 27.6 g (0.97 oz) 144.8 mm (5.70 in) 22.1 g (0.78 oz) 132.6 mm (5.22 in)
8 28.8 g (1.02 oz) 146.9 mm (5.78 in) 22.8 g (0.80 oz) 134.3 mm (5.29 in)

Information about the reproductive habits of gray-tailed voles is based on studies of captive animals.[17] In captivity, female voles as young as 18 days, weighing only 12.5 g (0.44 oz) are capable of reproducing.[17] Litters resulting from these younger females resulted in more offspring per litter, newborns of smaller mass, with decreased rates of newborn survival. The gestation period lasts 21–23 days.[17] The newborns weigh around 2.5 g (0.088 oz). The average litter size is around 4.5.[17] It is uncertain how frequently gray-tailed voles breed.[17] Breeding likely occurs year round.[18]

Gray-tailed voles recognize relatives based on familiarity. Under laboratory conditions, familiar gray-tailed voles produced fewer litters than unfamiliar individuals,[19] and pairings of relatives show lower pup survivorship than pairings of unrelated individuals.[20] Common foods of the gray-tailed vole in nature are thought to be grasses, clover, wild onion, and false dandelion (Hypochaeris radicata).[5] Published claims that the voles are omnivorous were presented without reference or evidence.[4]

Although they are now described as common, Bailey reported them to be so scarce that few specimens were available.[12] He also described them as being present east of the Cascades, which has subsequently been decided is not the case.[12] Population densities of the gray-tailed vole fluctuate widely over the course of the year.[18][4] There is not much data available to calculate population density in the field. However, based on studies in more controlled setting, estimates range around 600 animals per hectare.[18]

Human interactions[edit]

Gray-tailed voles are have been used in laboratory research projects.[21] They have been used to study effects of mineral deficiencies, such as selenium, which is lacking in Willamette Valley soils. They have also been used in studies on feeds that have been pretreated by fermentation, grains that have been sprouted, as well as clearance of radioactive isotopes.[21]

Gray-tailed voles can become so abundant within their range that humans may take measures to control populations.[5] Trapping the voles can be challenging.[15]

Conservation status[edit]

The conservation status of the gray-tailed vole is listed as "least concern" by the IUCN (International Union for Conservation of Nature).[1] No major threats to this common species are recognized. While the range of the vole is limited (less than 20,000 km²), it thrives in agricultural environments, so land conversion to such use is not problematic.[1] This species is also listed as secure by NatureServe.[18]

References[edit]

Footnotes:

  1. ^ a b c d e f g IUCN Red List 2008.
  2. ^ a b c d e f Verts & Carraway 1987, p. 4.
  3. ^ a b c d e Miller 1897, p. 67.
  4. ^ a b c d e f g h i j k l m n o p q r Verts & Carraway 1998, p. 317.
  5. ^ a b c d e Verts & Carraway 1998, p. 318.
  6. ^ a b Musser & Carleton 2005.
  7. ^ Verts & Carraway 1998, pp. 317-318.
  8. ^ a b Bailey 1900, p. 32.
  9. ^ a b c d Bailey & 1936, pp. 205.
  10. ^ a b Miller 1897, p. 68.
  11. ^ Verts & Carraway 1987, p. 1.
  12. ^ a b c Bailey & 1936, pp. 206.
  13. ^ a b c d Elliot 1904, pp. 179-180.
  14. ^ a b c d e Bailey 1936, p. 21.
  15. ^ a b c d e Verts & Carraway 1998, p. 319.
  16. ^ a b c d e f Verts & Carraway 1987, p. 3.
  17. ^ a b c d e Verts & Carraway 1987, p. 2.
  18. ^ a b c d NatureServe 2014.
  19. ^ Boyd & Blaustein 1985.
  20. ^ Verts & Carraway 1998, pp. 318-319.
  21. ^ a b Verts & Carraway 1998, p. 1.

Sources:

Further reading[edit]

  • Wolff, J. O.; Schauber, E. M.; Edge, W. D. (August 1997). "Effects of Habitat Loss and Fragmentation on the Behavior and Demography of Gray-Tailed Voles". Conservation Biology 11 (4): 945–956. doi:10.1046/j.1523-1739.1997.96136.x.  edit

External links[edit]

Data related to Microtus canicaudus at Wikispecies