Shrews may resemble mice but they are different

Shrews are one of the smallest mammals in North America and the smallest one resides in North Idaho--the pygmy shrew. The pygmy shrew weighs between two and four grams, roughly the weight of a pencil. Other shrews that reside in North Idaho include the American water shrew, masked shrew, montane shrew and vagrant shrew.

Shrews may look like mice but they are significantly different because they belong to a different order containing insectivores and they have pointed noses, small ears and tiny eyes. Like voles, identifying a shrew on the species level is difficult.

Shrews resemble mice but they have a pointed snout, small ears and tiny eyes

One unique aspect of a shrew, if you can catch one or find one dead, is that they all have reddish tips to their teeth. Shrews can also be identified by five toes on all feet whereas mice have four toes on the front feet and five toes on the hind feet.

All insectivores use senses besides sight to find food, mainly hearing, touch and smell. Shrews have many characteristics that allow them to forage for insects. 

Shrews have tiny eyes because they don’t rely on sight to find their food. Their pointed snout helps them burrow through soil to reach grubs including earthworms, insects, spiders and other small animals such as young mice, salamanders, snails and slugs. Some shrews even use echolocation like bats to find insects. 

Since their sense of smell is extremely important for finding food, a larger portion of their brain is devoted to their sense of smell. Once shrews find an insect, they catch the insect with their two enlarged, pincer-like upper front incisors that protrude forward. 

As big eaters, shrews eat at least their body weight in food each day. If they don’t eat frequently they may die of starvation so shrews store food in their nest. This voracious appetite doesn’t keep shrews from being picky eaters. Shrews prefer fresh food, even fresh stored food.

With a diet of insects, storing fresh food may seem unlikely but shrews keep their catch fresh by crushing the prey’s skull and biting off the legs. This keeps the insect alive until the shrew eats it. Shrews have sharp, pointed teeth adapted just for crunching on insect exoskeletons. 

While shrews may have a voracious appetite and a unique way of storing food, they are not on the top of many predators food list. Many shrews emit a musky odor from scent glands that resembles a skunk odor and effectively deters most predators except for owls. 

Like some mice, voles and lemmings, shrews are mainly nocturnal but will also be sporadically active during the day. They burrow in the leaf litter or humus layer to travel or travel in the burrows or runways made by voles and moles (also an insectivore). 

Like the water vole, the water shrew readily takes to water and lives around streams and ponds. The water shrew can even run on water because of the long, stiff hairs between its toes and along the sides of feet that trap air bubbles. 

Many of the shrews, mice, voles and lemmings survive the cold winter temperatures by living in the subnivian zone. This zone stays within one to two degrees of freezing regardless of the air temperature if there is adequate snow cover. 

Occasionally, tracks of these small mammals can be seen on the surface of the snow scurrying between trees or clumps of grass. However, the small mammals don’t stay on the surface long because they are more prone to predation, even if they possess a musky odor. 

Look for shorter tails on voles and lemmings

Scurrying around underground, in meadows and through leaf litter are several small, furry mammals. Last week, I wrote about the mice found in North Idaho and this week, I’ll focus on the voles and lemmings.

There are five native species of voles in North Idaho and one species of lemming: southern red-backed vole, western heather vole, meadow vole, long-tailed vole, water vole and northern bog lemming. Identifying individual vole species can be very difficult.

Voles and lemmings are grouped together in the same family and both are stocky-bodied and short-tailed with ears more or less concealed in their fur. Bog lemmings look like voles with really short tails. 

Compared to mice whose tails are almost the same length as their body, the tail of a vole is considerably shorter. The southern red-backed vole’s tail extends about 1.5 inches from its four-inch body. Voles and lemmings are also typically darker colored than deer mice.

Voles are active throughout the day because they feed on low-energy food that requires frequent eating. Voles and lemmings are primarily herbivores, foraging on fungi, seeds, nuts, berries, lichen, bark, green vegetation and roots depending on what is available in their habitat.

The habitats that voles occupy in North Idaho include damp forests with fallen logs, mountain meadows, clear-cuts, bogs, alpine areas, grassy areas, brushy areas, and along streams and ponds. 

Meadow voles are the most common vole in North Idaho and the most widespread vole in North America. Signs of meadow voles, like most other voles, are more common than seeing the vole itself.

Predators can find voles, lemmings and mice beneath the snow

Meadow voles create runways through grassy areas and leave piles of cut stems along the runways. The runways are especially visible after the snow melts since voles remain active in the subnivian zone (insulated layer between the ground and snow). Their globular nests of grass constructed in the subnivian zone are also revealed when the snow melts.

Meadow voles make air holes (roughly one-inch in diameter) up to the snow’s surface to allow carbon dioxide to escape from their subnivian tunnels. These air holes don’t have tracks leading up to them on the surface but meadow voles do travel on the snow’s surface and leave tracks. 

One aptly-named vole is the water vole which swims well and burrows into banks above and below the water level. Look for water voles along streams and ponds through alpine and subalpine meadows.

Less common than voles are bog lemmings. The northern bog lemming has almost no tail (it is three-quarters-of-an-inch long) and its body is nearly four inches long.

Northern bog lemmings are found in bogs, wet meadows, alpine tundra or openings in forests. Bog lemmings create runways on the surface like meadow voles and they dig shallow burrows underground. They also live in the subnivian zone in the winter.

Despite the differences between mice, voles and lemmings, they share the same rung on the food chain as an important food source for many predators, including weasels, foxes, owls, raptors, bobcats and coyotes. On the other hand, shrews have very few predators because of a special characteristic which will be revealed in next week’s column covering the last small, furry mammal. 

Small, furry critters include more than mice

Signs of the smallest mammals are more frequently seen than the animal itself unless you happen to see one scurry across the road. Mice, voles, lemmings and shrews are some of the smallest mammals in Idaho. 

While they all seem to be small, furry critters, there are significant differences between mice, voles, lemmings and shrews. One major difference is that shrews are insectivores while mice, voles and lemmings are rodents--two different orders in the classification system.

Mice exhibit a slender build with prominent ears, large eyes and well-developed whiskers. Voles and lemmings are relatively thick-bodied with small ears, snub nose, short tail and beady eyes. Shrews resemble mice but have pointed noses, small ears and tiny eyes.

Mice, voles and lemmings are rodents along with beavers, porcupines, squirrels, chipmunks and rats. All rodents share the characteristic of a prominent pair of incisors in the front of both the upper and lower jaws which supports their mainly herbivorous diet. 

The trails of mice, voles, lemmings and shrews are often seen more in winter than the animals themselves

There are two native species of mice in North Idaho: the American deer mouse and the western jumping mouse. The house mouse is an introduced species also found in Idaho and throughout the United States. 

The American deer mouse is a small- to medium-sized mouse that is nocturnal and active year-round. They range in color from dark-brown to orange-brown on their back with paler sides and a white belly. Their tail is equal to or slightly shorter than their body length (averaging 3.5 inches). 

Deer mice occupy almost every habitat because they eat a variety of food-- seeds, fruit, insects and subterranean fungi-- and store extra in caches. The woodland form of the American deer mouse capitalizes on food found in trees since it can climb well. 

Deer mice nest in hollow logs, underground burrows, birds’ nests, mattresses and among rocks. 

House mice share many characteristics with deer mice but the house mouse’s tail is less hairy and its coat more gray. House mice tend to have a pale or gray belly unlike the white belly of deer mice. 

House mice are also nocturnal and can climb well. They are most well-known for eating human food, soap, grain in agricultural areas and other items in buildings. House mice are less likely to be found in the woods and instead are found in agricultural areas, roadsides and in buildings in rural and urban areas. 

Another small rodent found in North Idaho is the western jumping mouse and is different enough from the other mice to be classified in its own family. Jumping mice have the same contrasting belly as the American deer mouse but its tail has a small tuft of fur at the tip.

Jumping mice have extremely long, narrow tails and exceptionally long, hind feet that allow them to leap six to ten feet in a single bound when alarmed. They are less likely to be seen since they are mainly nocturnal and hibernate. 

The jumping mouse hibernates for eight to ten months of the year. In the fall, jumping mice eat enough grass seeds, fruit, fungi and insects to accumulate a layer of fat for the winter. However, only about one-third of jumping mice survive hibernation. 

The best place to catch a glimpse of western jumping mice is along streams through mountain meadows. 

North Idaho’s three species of mice live in a variety of habitats but shouldn’t be mistaken for voles and lemmings, which I’ll cover in next week’s column.

Being green in winter isn’t easy

Compared to the Midwest, the forests of North Idaho are filled with more conifers than deciduous trees. Conifers keep our forests green through winter as do their evergreen counterparts hugging the ground. 

Evergreen plants, including conifers, can photosynthesize during winter despite the cold temperatures

While not as bright and vibrant as deciduous plants that steal the show in the summer, evergreen plants peaking through the snow keep the forest floor green in winter. One of the most obvious is Oregon-grape with its pointy leaves. A few other evergreen plants growing in the region include kinnikinnick, Labrador tea, bog cranberry, creeping snowberry, white and pink mountain-heather, crowberry and prince’s pine.

Unlike deciduous plants that lose their leaves in the fall, evergreen plants (as the name implies) stay green by keeping their leaves year-round. Every single leaf isn’t kept every year. Some conifers retain their needles for two to three years before shedding them. 

For the most part, evergreen plants keep their leaves to conserve energy. Often evergreen plants grow in areas where nutrients are sparse, so growing an entire set of leaves every year is costly. 

Evergreen plants are more prevalent at higher latitudes and higher elevations because the growing season is shorter. Growing all new leaves every year has to be advantageous for the plant instead of keeping the leaves year-round. 

White mountain-heather is an evergreen plant that grows at high elevations

For deciduous plants, one of the advantages of shedding leaves is the reduced chance of damage from snow and ice. An early snowfall when the leaves are still on deciduous trees exemplifies the damage that can occur when the branches become too heavy with snow and ice. 

Conifers possess a unique shape that allows for snow-shedding and their leaves (needles) are also smaller than deciduous leaves and catch less snow. 

A benefit of keeping leaves year-round is that evergreen plants can continue to photosynthesize during the winter. However, the rate of photosynthesis is significantly slower in the winter than in the summer. 

Photosynthesis is the process of using light energy to convert carbon dioxide and water into sugar and oxygen. Light and carbon dioxide are available in the winter but water is less available. 

Water is a key factor for evergreen plants in winter. Water doesn’t move as quickly from the roots to the leaves in winter and less water is available from the soil. Often evergreen plants rely on water stored in the stems for photosynthesis. Some plants can even obtain snow meltwater through their leaves or thinnest bark. 

With precious water in the leaves, evergreen plants have to be careful not to loose it and they have several adaptations to prevent water loss. Water loss happens because water vapor moves from areas of high concentration (inside leaves) to areas of low concentration (air). 

Most evergreen plants have a waxy coating on their leaves to reduce water loss and also to protect new growth from ultraviolet radiation. Without a waxy coating the leaves would dry out quickly. 

Oregon-grapes have a waxy coating on their leaves to prevent water loss

Evergreen leaves also have tight stomatal closures which are holes in the leaves that allow for air exchange (carbon dioxide in and oxygen out). 

Other ways evergreen plants reduce water loss are by having dense foliage to reduce air movement and by having a fuzzy underside on leaves to create a zone of insulation. Both reduce the concentration gradient immediately outside the leaf and, therefore, help reduce water loss. 

Even if photosynthetic rates are slow in winter, evergreen plants can take advantage of spring warmth and increasing sunlight to jumpstart their growing season. For low-lying evergreen plants, spring and late fall may be the only time deciduous vegetation doesn’t overshadow them and block their sunlight.