By Peter Kolb

A quiet walk at dawn or dusk might yield many sounds from rustling to squeaking if you listen carefully, but we rarely see the culprits. There are at least seven species of mice, eight species of voles, and 11 species of shrews found across Montana. Do you know their names and what they do? See identifications:

  1. House mouse – Mus musculus. Although non-native to Montana, the house mouse is a worldwide invasive species. House mice have the characteristic large, mostly hairless ears, thin tails, and tiny bodies that we envision as a typical “mouse.” They are the most common species to find inside a home because they’re so adaptable to human presence, eating most food scraps. They build their nests in walls or dark attics and basements, and spend most of their time hidden from view.
    Grey looking mouse with small round ears and black eyes.
  2. Eastern Deer mouse – Peromyscus maniculatus. The Deer mouse in Montana measures approximately 6 1/2 inches long, including its tail, and varies in color from pale gray to dark reddish-brown on its back and upper tail. Its belly, legs and feet, and the underside of its tail are white. Sharp claws allow them to climb trees and houses. In addition to spending time in forests, this species is also commonly found in houses. The Deer mouse’s large, lightly-haired ears and big eyes are suited for its nocturnal habits and under-the-snow winter life. Eastern Deer mice are one of the most widespread mice in Montana. Its various subspecies are spread all over the country. Eastern Deer mice prefer to nest high up in hollow trees. They are omnivorous, preferring mainly seeds and insects.
    Grey mouse with white underbelly, long pink tail, small round ears, and black eyes.
  3. White-footed Deer mouse – Peromyscus leucopus. Found mainly in eastern Montana. Like other mice in Montana, it carries and spreads disease. Many rodents can carry disease-causing pathogens without getting sick, making them ideal carriers for these germs. For example, this mouse transmits hantavirus, which causes severe disease in humans, and the bacteria that cause Lyme disease.
    Small brown mouse with white underbelly, black eyes, and larger round ears.
  4. Meadow vole – Microtus pennsylvanicus. Often mistakenly called a “field mouse” but is actually a vole. Voles tend to be ground dwelling and are identified by their small eyes, ears and shorter tails. Eastern Meadow vole uses burrows for nesting and shelter. They create woven grass nests placed in the burrows or under logs. They prefer grassland or open forest habitats. Meadow vole is a dietary generalist eating garden plants, flowers, crops, and grasses. They are uncommon in structures like houses.
    Medium sized dark brown rodent with a short snout and small ears and eyes.
  5. Southern Red-backed vole – Clethrionomys gapperi. The Southern Red-backed vole has a blunt nose and short ears. It is approximately 6 inches (152 millimeters) long when fully grown. The wide, reddish band which distinguishes it from other voles in Montana traces over its back from the forehead to the base of a short tail. Found across most western forested sites, it is a favored prey of Pine martens in northwest Montana. Living in simple globular nests (75 to 100 mm. in diameter) lined with grass, stems, leaves or moss, it typically does not construct runways. Diet consists of plants, nuts, seeds, berries, mosses, lichens, ferns, fungi and arthropods. A favorite food is mycorrhizae mushrooms and truffles and they are credited with spreading these important fungi across the forest floor.
    Longer bodied, brown rodent with small round ears and black eyes.
  6. Montane vole – Microtus montanus. Most common from mid- to- higher elevation forests with evergreen shrub groundcover, also in timberline krummholz, and alpine tundra. Its back will be blackish-brown or black, with a gray cast to the fur. Pale, buffy sides, a whitish belly and dusky-colored feet help it blend into dry grasslands. This rodent’s ears are small enough to be hidden in its fur. Very similar to the Western Heather vole (Phenacomys intermedius) that is gray with a brown to dark-brown cast to the fur, white face, and silvery belly. Found in montane yellowpine/Douglas-fir forests with bearberry/twinflower understory where it prepares winter food caches of twigs and berries. Also does not tend to construct runways. May also be important vector of mushroom spores. Scat tends to be orange in color.
    Black rodent with brown undertones, small round ears, and black eyes.
  7. Long-tailed vole – Microtus longicaudus. Unlike other voles the tail will be nearly 3 inches long and it has large, hairy ears. Upper body color may be anywhere from a dark brown to grayish-brown, with streaks of black-tipped hairs. Sides appear more gray and the belly can be gray with a dull buffy wash or whitish.
    Grey colored rodent with light brown undertones, a short snout, small round ears, black eyes, and a long tail.
  8. Western Jumping mouse – Zapus princeps. The Western Jumping mouse prefers being near water, including springs and streams. Ideal habitat includes riparian, herbaceous wetlands, grasslands, mountain meadows, and marshes but found in most forest settings as well, especially disturbed (harvested or bettle killed areas. They rely on dense (>25% herbaceous), tall grasses (9-13 in/24-35 cm) for cover. Western Jumping mice eat insects, grass and forb seeds, and the stems and leaves of herbaceous plants. They do not cache food but hibernate, losing as much as 18 percent of their body weight from the previous year. Its hind legs are longer and stronger than its front legs, and it can travel with long jumps like a kangaroo.
    Brown and black rodent with long back legs, small round ears, and black eyes.
  9. Western Harvest mouse – Reithrodontomys megalotis. Unlike other mice in Montana, the Western Harvest mouse is a strict herbivore and does not typically consume insects. Instead, it feeds primarily on fruit, grasses, and seeds. Its range extends from southwest British Columbia, southeast Alberta continuously to west Texas, northeast Arkansas, northwest Indiana, southwest Wisconsin, and the interior of Oaxaca Mexico. The harvest mouse has brownish fur with buff sides, a white belly, and an indistinct white stripe on the fur along the spine. It may look like the common house mouse, but its front teeth have grooves, whereas the house mouse does not.
    Small, skinny rodent with brown fur, white underbelly, small sound ears, and black eyes.
  10. Masked shrew – Sorex cinereus. There are 11 shrew species across Montana, the most common are the masked shrew and Dusky shrew. Shrews are unique and are not in the rodent family, but related to hedgehogs and moles and prefer to be carnivorous but will eat seeds and fruits. They have a fantastically high metabolic rate and must eat their own body weight or more every day. Many use a form of echo location from high pitched squeaks. They may have 2–5 litters of 2–8 offspring a year, which helps their species survive as their average lifespan is only a little more than a year. The masked shrew is considered medium-sized for its species with adults averaging 3 inches in length. Shrews have black-tipped front incisor teeth and powerful scent glands that can have adverse effects on domestic house cats and dogs that usually vomit them up after eating them. This is why they are commonly found dead in backyards but not eaten. Birds, snakes and other native predators will eat them.
    Brown rodent with white underbelly, long skinny snout, miniature black eyes, and short ears flush with it's head.
  11. Vagrant shrew – Sorex vagrans. At elevations below 5000 feet, usually found in Douglas-fir, lodgepole pine, western larch, grand fir, and western red cedar forests. They eat insects, other shrews, vegetable matter, and insect larvae. Apparently they will also eat plant seeds, carrion, and some mushrooms.
    Black rodent with grey underbelly, skinny snout, small short ears, and miniature black eyes.
  12. Dusky shrew, Montane shrew – Sorex obscurus. Found in western Montana, high-altitude spruce-fir forest, alpine tundra, or as low as 3000 feet in mid-altitude forests. Occurs along streams and rivers east of the Continental Divide and in isolated mountain ranges in central Montana.
    Round brown rodent with skinny snout, small ears, and miniature eyes.
  13. Western Pygmy shrew – Sorex eximius. The smallest mammal found in Montana, it is about half the size of the Masked shrew. They may spend their entire lives in several square meters of land area. Like other shrews, they never hibernate and utilize tunnels in the soil and grass created by other fauna. Previously the Western Pygmy shrew was called the Pygmy shrew (S. hoyi). However, recent analysis of the genetic structure of this species has provided support for splitting it into several species with the Western Pygmy shrew occurring in Montana. Their limited-distance-travel probably predisposes them to develop unique genetics across landscapes due to genetic drift and isolation.
    Very small brown rodent with a tiny head and short tail.
  14. Western Water shrew – Sorex navigator. A large, semiaquatic, blackish-gray shrew with a long, bicolored tail and large hind feet, fringed with short, stiff hairs. Total length is 5.5 to 6.3 inches including a 2.4 to 3.1 inch tail. The dense fur is glossy, blackish-gray above and paler or silvery beneath. Scats of Western Water shrews are quite distinctive, black and granular in structure, being full of remains of invertebrate exoskeletons. They are often deposited in middens on the banks of streams, in surface burrows, at burrow entrances, in the lee of rocks at the stream edge, or even sometimes quite prominently on the tops of stones.
    A black rodent covered in water with a skinny snout and black eyes.

Photo credits: Photos were obtained from a variety of sites such as the Montana Natural Heritage Program – Field guide (mtnhp.org), U.S. Forest Service, and those taken personally by Peter Kolb. Southern Red-backed vole photo credit: Ryan Stephens, University of New Hampshire. Information was also obtained from a variety of sources, but mainly from the Montana Field Guide. Information on some mice, voles and shrews can vary and is limited to very specific research papers.