Microtus montanus
(Montane Vole)

Description:
Montane voles is about the same size as the meadow vole, but it is lighter on top; brownish to grayish-brown sometimes mixed with buff or gray which gives it a grizzled appearance. The ventral side is silvery gray. It has a bicolored tail that is about 2.5 times as long as the hind foot. It is not easy to distinguish from the meadow vole. Total length is 5.3 to 7.6 inches (132-190 mm), tail length is 1.4 to 2.3 inches (35-58 mm), and they weigh 1.2 to 3.2 ounces (34-90 g).

Range:
From southwestern British Columbia, south through western U.S. to Arizona and New Mexico.

Habitat:
The montane vole seems to prefer slightly drier habitat than the meadow voles and where they co-occur, the montane vole favors drier habitat. They are found in alpine meadows in their southern range, and in mountain valleys in the northern part of their range. They generally prefer wet meadows and cropland (especially fields and pastures of grass and legumes along fence rows), and grassy areas by streams and lakes. In Idaho, are typically found in moist, mountain meadows and high valleys, but also in shrub steppe (especially crested wheatgrass).

Diet:
Eats grasses and sedges, and leaves, stems, and roots of wide variety of forbs. In Idaho, diet includes grass shoots, seeds, bulbs, tree bark, shrubs, and agricultural crops.

Ecology:
Like the meadow vole, they live in runways and burrows in dense grass. These runways can often be observed by looking carefully at ground level in dense grassy habitat. They are active throughout year, and tend to by diurnally active. Populations may fluctuate dramatically, as their populations exhibit a 3 to 4 year population cycle between highs and lows. In a Utah study, peak population density reached 375-560 per 2.5 acres (1 ha). Utah researchers have also found that a specific chemical factor in their spring food (vegetation) stimulates reproduction. Social organization changes according to population density. Males and females both maintain territories. The male territory is larger and excludes other males but includes several females. The female maintains a small territory, and during estrus she will drive away other females but not males or her young. During periods of low population densities, the female moves to a new territory after her litter is weaned, leaving her young behind. During high population densities the female forces her young to disperse, causing extremely high mortality for the inexperienced young. An Idaho study suggested that cattle grazing may negatively impact populations. This species is important prey to many avian and mammalian predators.

Reproduction:
The primary breeding season is from March to November, but it is capable of breeding year-round, depending on population density. Females can breed shortly after giving birth, and young females can breed at an age of only 3 weeks. A female usually produces 2 to 3 litters per year. Average litter size is about 6 (in northwestern Wyoming, litter size peaked at 3 to 4 year intervals). Again, an incredible reproductive potential exists in this species, but very high mortality rates keep the population in check. Its longevity is probably similar to the meadow vole.

Conservation:

Status:	Unprotected nongame species
Global Rank:	G5
State Rank:	S5

Important State References:
Smolen, M.J. and B.L. Keller. 1979. Survival, growth, and reproduction of progeny from isolated high and low density populations of Microtus montanus. J. Mammal. 60:265-279.