Microtus canicaudus

The gray-tailed vole (Microtus canicaudus) also known as the gray-tailed meadow vole or gray-tailed meadow mouse, is a rodent in the genus Microtus (small-eared 'meadow voles') of the family Cricetidae. Voles are small mammals, and this species lies roughly in the middle of their size range. First collected in 1895, it is endemic to the Willamette Valley, Oregon, and Clark County, Washington, in the Pacific Northwest region of North America. Historically, they were found in the prairie areas of the Valley and, though many of these areas have been converted for agricultural purposes, these animals remain common. For reasons that remain unclear, vole population densities in any area may fluctuate widely from season to season and year to year. They are preyed upon by owls, hawks, and carnivorous mammals, and their parasites include fleas and ticks. These voles build underground burrows and complex tunnel networks, which they sometimes share with other burrowing animals. Relatively little is known about their behavior in the wild, because they are elusive and unlikely to enter traps. The scientific name of the gray-tailed vole is Microtus canicaudus. The generic name Microtus derives from the Ancient Greek words μικρός (small) and οὖς (ear). The species name canicaudus derives from the Latin canens (gray) and cauda (tail). The gray-tailed vole was first described in 1897 by Gerrit S. Miller in the Proceedings of the Biological Society of Washington. The type specimen was collected in McCoy, Oregon, on December 1, 1895, by B.J. Bretherton. Miller's initial examination included the type specimen and eleven others. Two from his collection had been obtained in Beaverton. The remaining specimens, collected in McCoy, were part of the US National Museum Biological Survey under C. Hart Merriam. The gray-tailed vole is monotypic, but there are some differences between specimens obtained on either side of the Columbia River. It appears to be a sibling species of the montane vole (Microtus montanus) or of Townsend's vole (M. townsendii). It was classified as a geographic race or subspecies of the montane vole by Hall and Kelson in 1951, but laboratory analyses, including electrophoresis and karyotype evaluations, subsequently confirmed that they are two separate species. The karyotypes of the montane vole and the gray-tailed vole are dissimilar in terms of homology in 6 of 22 autosomal arms. The quantity and distribution of heterochromatin among both X chromosomes and autosomes is different as well. The two species are allopatric, but not contiguously so. The gray-tailed vole is a small mammal in the middle of the size range for voles in general. The fur on the back is yellowish-brown or yellowish-gray. They have a short tail, black or brown above and grayish below. The young have gray fur on the underside and a darker, 'sooty' gray on the back. The feet of the young are dusky, and they have a gray tail with a black stripe. They are similar in size and overall appearance to the montane vole, but with a more yellowish fur and a grayer tail. The type specimen measured 135 mm (5.3 in) in total length. The tail vertebrae measured 33 mm (1.3 in) and the hind foot measured 20 mm (0.79 in). Typical adults average 141 mm (5.6 in) in total length, with a 35 mm (1.4 in) tail. The feet measure 20 mm (0.79 in) and the ears 12 mm (0.47 in). On each side they have an upper and lower incisor and three upper and lower molars, for a total of 16 teeth. Gray-tailed voles are sympatric with Townsend's vole (M. townsendii), with which they share many similarities. They can be distinguished by appearance, because Townsend's vole has darker colorings, a longer tail, and differences in the structure of the hard palate. Gray-tailed and montane voles also differ in some aspects of hard palate structure, especially the incisive foramina. The gray-tailed vole shares its geographic range with the creeping vole (Microtus oregoni) as well. The gray-tailed vole has a sturdier build, larger eyes, and some differences in the upper molars. The gray-tailed vole is endemic to the Willamette Valley, Oregon, and to Clark County, Washington. Its range in Oregon extends from Scappoose and Gresham in the north, through the Willamette Valley to around Eugene. Reports of the species east of the Cascades have been called into question. Gray-tailed voles are prevalent in agricultural areas: they are found in and around pastures, hayfields, grain fields, and disturbed habitats. They once inhabited grassy prairies of the valley. These prairies were burned annually by Native Americans, with uncertain effects on vole populations. Vernon Orlando Bailey describes the Willamette Valley as part of the humid division of the Transition Zone. Annual precipitation there is 40 in (100 cm), falling mostly in the winter. The valley is warmer and drier than the surrounding hills, less heavily forested, and better suited to agricultural use. In 1901, zoologist Edmund Heller visited McCoy, where the type specimen of the gray-tailed vole had been collected. The account of his journey is relayed by Daniel Giraud Elliot, referring specifically to the terrain inhabited by the gray-tailed vole. 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.' He 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.'