Door to Nature: Mice, Voles and Shrews

It’s been a lackluster winter for outdoor sports and snow enthusiasts. We have had very few good snowfalls and rain turning everything to ice in between, making conditions poor for cross-country skiing and snowshoeing.

However the white-footed deer mice, meadow voles and short-tailed shrews are doing well. Some of the more recent snows of an inch or less revealed the pathways of the shrews and voles as they tunneled under the snow on their way to find seeds near the bird feeders.

Wisconsin’s smallest mammal is the American pygmy shrew. Adults weigh about one-fourteenth of an ounce and are slightly less than two inches long. Like all other shrews in this state they do not hibernate. In fact their rate of metabolism is so rapid that they remain active in search of food much of the day and night.

About the only really good look at a shrew we ever get is when one is caught in a mousetrap. Most often it turns out to be the common or cinereus (meaning ashen, due to its color) shrew. Their body length is around 3 to 4 inches with a tail of about 1.5 inches.

This dead short-tailed shrew has a pointed snout, furry tail and very tiny ears.

Occasionally we find one dead in the morning on the sidewalk in the front yard. This is how we came across a little short-tailed shrew recently. Very likely some predator, such as a weasel or even a cat, caught the shrew and killed it. A gland on the side of the shrew’s body secretes a vile-tasting substance apparently making the animal very unpalatable.

Most shrews conceal themselves during daylight hours. Consequently few people ever see them. When they do get a glimpse at one, or catch one in a mousetrap, they will usually call it a mole because of its long, pointed, streamlined snout. Moles have considerably wider forefeet than shrews.

All shrews of this state belong to the order Insectivora. Their food includes insects and their larvae as well as mice, salamanders, mollusks, earthworms, frogs, slugs, snails, nuts, seeds and berries.

Their reputation of being ferocious and bloodthirsty is true. A victim, such as a mouse, receiving venomous bites from the shrew, suffers a sudden lowering of blood pressure, slowing of the heart and inhibition of breathing. They usually are incapacitated in less than one minute.

Shrews, pugnacious and aggressive, are slaves to their fantastic appetites. Their very fast pulse, approximately 700 beats per minute, reflects their accelerated rate of digestion and food use. Their front teeth are slightly hooked inward providing them with a firm grip of their victims.

This animal’s enemies, natural and unnatural, include the fox, house cat, owl and weasel. I presume that, unless the predator is extremely hungry, far more shrews are killed than are eaten.

The animal considered to have always been the most abundant mammal in the deciduous forests of Wisconsin and has a home range of only one-quarter of an acre is the white-footed mouse, also called the deer mouse.

A number of years ago this seven-and-a-half-inch dynamo showed us who was boss in our garage. Roy had been storing dried corn cobs in a burlap bag to use for his hanging squirrel feeders. We learned, after my car had an oil change and new filter, that the air cleaner had been completely filled with corn kernels. Then when Roy went to start his old Ford tractor, parked in the next stall, he found the little squirts had completely filled the muffler and tailpipe with corn. Well it didn’t take long to find a better place to store the corn cobs!

Most people living in wooded areas are bound to eventually have confrontations with white-footed mice. A dozen or more species and around 50 subspecies have been studied and identified in North America. At least three distinctly different races live in Wisconsin and their ranges do overlap.

Their body length of 7½ inches includes a tail that is around 3½ inches long, brown above and cream-colored below. Very likely this long, wiry tail, covered with transverse ridges, aids the agile animal in climbing and perhaps jumping.

The meadow voles are very active at night and a thin snow cover can reveal the tunneling paths they make in search of food.

Shiny, beady-black eyes, funnel-like ears and long sensitive whiskers characterize the white-footed mouse. Cinnamon-rufous above and white below, it surely is a beautiful little animal.

Their hind legs are longer and stronger than their front legs, and their hind feet are also longer and larger. Surely this aids them in climbing, one of their well-documented accomplishments. In fact they prefer to nest in rotten, hollowed-out trees where their entrance may be several feet above ground.

These mice have become important vectors in the spread of Lyme disease. The larvae of the deer tick, which are the first stage of development in spring, need a blood meal and that is usually on the white-footed mouse. If the mouse has been infected with the disease the tick larvae will pick it up and continue to carry it into the adult stage when they are found in autumn of the following year on the wild deer population.

What mice lack in size they make up for in numbers. Females mature at about a month of age and can conceive at around ten weeks or less. Young are born between 23 and 28 days after mating and one female can produce as many as four broods between April and November.

The meadow vole, sometimes called a field mouse, is different from a mouse in having shorter ears and tails. Their tails are furry unlike the naked tails of the deer mice. They can have 3 to 10 young per litter and may produce several litters per year. Most voles don’t live more than 12 months.

They are “fast food” for weasels, bobcats, foxes and owls. They can have quite a network of runways in open fields, are active throughout the year and usually feed at night. In summer they eat cut grass, clover, alfalfa and grain. In winter they tunnel under the snow to gnaw the bark of trees and shrubs.

As much as some people dislike mice, they are a link to many wild “food chains,” benefitting people by eating numerous weed seeds and insects, especially insects in their egg and larval stages. It has also been determined that mice inadvertently plant a lot of wildflowers while consuming some of the seeds. Unfortunately they can cause plenty of problems for orchards and farms.

If hawks and owls had their say, surely they would place mice and voles near the top of the list of our state’s most important mammals.

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