148.

Montane Vole

Microtus montanus

French: Campagnol montagnard / German: Rocky-Mountains-Wiihimaus / Spanish: Topillo de montafa

Other common names: Pahranagat Valley Montane Vole (nevadensis)

Taxonomy. Arvicola montana [sic] Peale, 1848, near Mt. Shasta, headwaters of Sacramento River, Siskiyou County, California, USA.

Fifteen subspecies are recognized.

Subspecies and Distribution.

M.m.montanusPeale,1848—SCOregon,NE&ECCalifornia,andWNevada,USA.

M.m.amosusHall&Hayward,1941—narrowrangefromNEtoSEUtah,USA.

M.m.arizonensisBailey,1898—BlueRangeofEArizonaextendingintotheGilaregionofWNewMexico,USA.

M.m.canescensBailey,1898—fromSCBritishColumbia,Canada,StoSCWashington,USA.

M.m.codiensisS.Anderson,1954—extremeSCMontanaandNWWyoming,USA.

M.m.dutcheriBailey,1898—restrictedtohigherelevationsofSSierraNevada,CCalifornia,USA.

M.m.fucosusHall,1935—restrictedtoSENevada,USA.

M.m.fususHall,1938—extremeSEUtah,W&SColorado,andNNewMexico,USA.

M.m.micropusHall,1935—SEOregon,SWIdaho,N&CNevada,andextremeWUtah,USA.

M.m.nanusMerriam,1891—WWashington,NC&WOregon,Idaho,SW&CMontana,W&SWyoming,extremeNENevada,N,WC&SWUtah,andNColorado,USA.

M.m.nevadensisBailey,1898—restrictedtothevicinityofAshMeadows,SENevada,USA.

M.m.pratincolaHall&Kelson,1951—WMontana,USA.

M.m.rioularisBailey,1898—restrictedtothetypelocalityinSWUtah,USA.

M.m.undosusHall,1935—restrictedrangeinWCNevada,USA.

M. m. zygomaticus S. Anderson, 1954 — NC Colorado, USA.

Descriptive notes. Head-body 116-151 mm, tail 24-69 mm, hindfoot 14-27 mm; weight 37-85 g. Males and females are similar in weight; adult males average 47-9 g, and adult females average c.47 g. The Montane Vole is medium-sized and morphologically variable acrossits distribution in western North America; largest individuals are found in south-western populations, and individuals in northern populations tend to be smaller. Dorsum is brown, with buffy or gray wash and black-tipped hairs; sides are paler and buffy; and venter typically is white to gray. In south-western populations, pelage is darker, and red, gray, or brown hairs lighten pelage in northern and eastern populations. Pelage color of females is more variable than that of males. Tail is relatively short, dark brown to black above and lighter gray below. Hip glands can be found on subadult males and older females, but they are largest on adult males. M? has four closed triangles, and foramina are great than 5 mm long and constricted posteriorly. Chromosomal complement of most populations is 2n = 24, FN = 44, but some Oregon populations have 2n = 22, FN = 40.

Habitat. Variety of habitats but highest abundancesin areas with high herbaceous and grass cover. In southern part of the distribution, Montane Voles are restricted to highelevation grassy meadows, but farther north, montane and intermontane areas with high grass cover are inhabited. Distribution of Montane Voles overlaps with other species of Microtus, including the California Vole ( M. californicus), the Long-tailed Vole ( M. longicaudus), the Prairie Vole (M. ochrogaster), the Meadow Vole ( M. pennsylvanicus), or the North American Water Vole ( M. richardsoni). In regions of overlap, species often segregate at different elevations or tend to occupy different habitats. Some authors suggest that less dominant or aggressive species occupy less preferable habitat when more competitive congeners are present.

Food and Feeding. In one study of stomach contents, green leaves and forbs were 85% of the diet of Mountain Voles; grasses made up less than 10%. Frequently eaten forbs were vetch ( Vicia americana, Fabaceae) and evening primrose ( Eremothera minor, Onagraceae); fungi were also eaten when green vegetation was not available. Grass is often the main food when a single species of grass, such as crested wheatgrass ( Agropyron cnistatum) or salt grass ( Distichlis spicata), both Poaceae, dominates an area.

Breeding. Breeding season of the Montane Vole typically begins after snowmelt in April-May. Depending on elevation and latitude, breeding continues through summer until September—November, with multiple litters produced. When populations are in the increasing phase of a cycle, female Montane Voles reproduce below snow. Gestation is 21 days, and litters have 2-10 young. Younger females tend to have fewer young. Females stay with their young until they are c.15 days old and then construct new underground nests of grass for each new litter. Males and females do not share nests during breeding. In Wyoming, each cycle has a periodicity of 3-4 years, and spring precipitation seems to impact litter size and population cycles. Largest litters correspond to increasing phase of the cycle, and smallerlitters are seen during declining phase.

Activity patterns. Montane Voles can be active night and day and throughout the year. During the hottest months, they shift activity to early morning and late afternoon and evening to avoid hottest temperatures.

Movements, Home range and Social organization. Montane Voles are semi-fossorial and dig burrows or use gopher burrows. Males and reproductive females are territorial toward members of the same sex. Males mark their territories with urine, feces left in runways, and anal dragging and scooting that deposits glandular secretions. Males also mark their underground tunnels by rubbing their hip glands. Male-male aggression is pronounced just after spring snowmelt when territories are being established. When densities are high, sex ratio for reproductive individuals may approach a single male for five females.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Subspecies nevadensis is of conservation concern and maybe extinct.

Bibliography. Drabek (1994), Hafner et al. (1998), Jannett (1980, 1982, 1984), Judd et al. (1980), Musser & Carleton (2005), Negus et al. (1992), Pinter (1986), Sera & Early (2003), Vaughan (1974).