Volume VII, No. 1, Fall 1979




UNTO THE LEAST OF GOD'S CREATURES

PRAIRIE MEADOW MICE

by Melinda Stewart and Donna Scott


Wee, sleekit, cowrin', tim'rous beastie, O, what a panic's in thy breastie!

These lines from Robert Burns' poem, "To a Mouse," seem to describe the furry brown creature as it crouched, exhausted, in its strange surroundings. It had searched and searched for a way back to the freedom of fields, thick with succulent plants and flowers. Now it sat in the corner, its dark beady eyes full of panic.

This prairie meadow mouse had just come from one of its feeding grounds and was running to the safety of its tunnel when we chased it down. Later, we took it from its native habitat and put it in a box, foreign to its understanding. Now it cowered, its senses full of smells it had never smelled, sights it had never seen and sounds it had never heard.

It didn't know what its role was in its new environment. The mouse recognized nothing now that it could associate with its life before today. Its inability to understand what had happened and wondering what would happen increased by the second.

Once again man had tampered with nature by disturbing a small but significant part of the cycle of life. Though this mouse was one of the least of God's creatures, he had an important role in the balance of nature.

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One part of the mouse's role stimulates new plant growth by its practice of cutting grass to eat. Before the pioneers settled the plains, the prairie grass was kept thinned by fires. As settlers arrived, they stopped the fires, and soon the grass and roots became thick, making plowing difficult. The meadow mice helped by cutting down the grass and by loosening the soil with their tunnels. By making tunnels, the mice also continuously mix wastes and their food stores with the soil. In this way the nutrients from the food they eat are quickly returned to the soil. The body of the mouse itself is an important link in the food chain cycle--from the grass it eats to its flesh and through the bodies of the larger animals which prey on it back to the soil.

The prairie meadow mice are large eaters, eating their own weight in greens every twenty-four hours. Usually they eat tender stems, leaves, roots, tubers, flowers, seeds, fruits or grasses, sedges, shrubs, vines and bark, but in times of low food supply, they will eat insects, snails, crayfish and even other mice. Succulent plants are their common food and because of this they probably don't require water.

In their runs they pile grass stems that they have cut close to the ground and hauled down to get the seed. Sometimes they store their food in hollow stumps, but most frequently in their tunnels in storage chambers near the nests. A storage chamber may contain up to two gallons of roots, bulbs and tubers.

The mice clip the stems, clearing a path from the safety of their burrows to new feeding grounds. Green plants constitute the majority of the mouse's diet. Either it eats the stems then or takes them to the storage bin in its underground nest to save until weather makes food scarce. Should fate await it on some excursion, another mouse or shrew may find and feed upon the storage. If not found, sooner or later decomposers begin to break down the storage and return it to the soil.

Many larger animals feed upon these vegetarians. An owl, with its soft, close fitting feathers makes very little noise as it approaches an unsuspecting mouse and grabs it in its strong talons. Returning to a roost it tears the mouse apart with its sharp beak and swallows it. The strong enzymes in the owl's stomach begin to eat away at the mouse's carcass, first dissolving the meat and insides, then compressing the indigestible bones and hair into an oval shaped pellet which it regurgitates and lets drop to the ground.

An unfortunate mouse is often captured by the sharp teeth of a coyote Whose principal food is mice. Through the process of digestion, coyote droppings fall to the ground and are broken down by various bacteria, thus returning to the soil the food one root absorbed before a mouse ate the plant, a coyote or owl ate the mouse and the bacteria ate the droppings.

Thus the mouse is an important food source in nature and its population levels influence the population levels of other animals, including game species. Because mice are such an easy and common prey, their availability reduces predation on game species like rabbits and quail and on domesticated animals.

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Other predators of mice are hawks, foxes, domestic cats and dogs, bobcats, oppossums, shrews, raccoons, badgers, minks, striped and spotted skunks, weasels, snakes, crows, bullfrogs and turtles. Mice are small enough that predators either swallow them whole or kill them by crushing the head.

Sometimes we catagorize the meadow mice with other more destructive and hated members of the rodent family, such as the imported house mouse and the rat. Prairie meadow mice do cause damage, but unlike these other two, they almost never go into a barn or house to eat stored grain. Their arena is the fields and orchards. There they often eat sprouting corn, garden vegetables, corn germ and alfalfa. In the winter they may chisel the bark of young trees. It is estimated that a hundred mice per acre in one year will eat 300 pounds of alfalfa hay. They waste twice that much by cutting and pulling down the stalks to eat the grain. They can cut down as much as thirty percent of a crop during high peak population times, but even during these times, they rarely go near civilization.

Not only does the meadow mouse differ from other mice in their eating habits, they are also different in physical appearance and in activities. Different species can be identified by their skull and teeth, but there axe other more evident ways with the naked eye. Their bodies, usually about five inches long from the tip of the nose to the tip of the tail, are stockier and their fur is heavier. Their coats are usually various shades of brown, such as chestnut, chocolate and sandy, though sometimes they are black or salmon colored. The belly and legs are tan and the tail is dark.

They live in fallow fields, fields of alfalfa, bluegrass, clover and lespe-deza, in thickets, along fence rows under shocks of corn and small grain where heavy layers of dead leaves and dense grass provide cover, and in deciduous, oak-hickory, mixed hardwood and pine forest. Meadow mice are found around the world from the Arctic tundras and hot deserts to coastal marches.

Prairie meadow mice build runways to feeding grounds both on top of the ground and underneath which cover an area about the size of a tennis court floor. Runways above ground, which are one to two inches in diameter, may be a thin layer of trampled grass chewed close to the ground, stems or bare ground. They are kept clear by cropping all sprouts that grow in the path. Dirt removed from the tunnels is sometimes carried and scattered along the runway for pavement.

Little mounds of about two inches mark where the surface runways go underground. Although mice may use tunnels of other mice, shrews and moles, they dig their own tunnels with their lips tightly closed to prevent getting dirt into their mouths. Their holes are about two inches in diameter and can be recognized by piles of dirt which have been excavated from the tunnels. They are from four to twelve or more inches deep.

Although mice live together in colonies, each mouse maintains its own runaway. Territories often overlap so large numbers of individuals are packed into a small area. The mouse has a normal home range of one-fifteenth of an acre, but the males wander farther than females from their home range.

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Mice are thought to be one of the commonest mammals in the world. The species of prairie meadow mice is only one of many species.

Shown here is an opening to a tunnel and a run in the grass.

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The mice build nests both above and below ground. Above ground the nests are in clumps of vegetation or under debris. Underground the nests are from two to eighteen inches deep, seven to eight inches long, four to six inches wide and about four inches high. Woven from coarse grass and lined with fine pieces of grass and other soft material, the nests are usually ellipsiodal-shaped with one to two entrances.

Mice are generally active all day and night because they live on a four hour schedule of eating the first part and sleeping the last part, but they usually get only two or three hours of sleep in every twenty-four hours. They quite often squeak, squeal, growl or chatter when frightened or angry. They may also stamp their front and hind feet and on occasion may fight.

They are neat and clean, continually grooming their fur. They even set up a communal toilet along their runways where piles of their green pellet-like droppings are deposited. They swim voluntarily. When swimming on the surface, most of the back is exposed. When swimming underwater, air bubbles are trapped in the fur and help to keep the body from becoming wet. Some mice have been observed swimming distances of ninety feet.

In the winter meadow mice don't hibernate. They travel in their runs and tunnels and under leaves to find food on warmer days. On very bad days they use their food caches.

Perhaps one reason they are so maligned is that the meadow mouse is one of the most prolific mammals known. A female can be pregnant and nursing at the same time and she is capable of breeding at three weeks of age. Since the male doesn't reach breeding age until five weeks, the difference in their maturation age helps prevent the chances of litter mates breeding. Breeding season occurs throughout most of the year with peaks in the spring and fall. Numbers and sizes of litters are influenced by the abundance of food, temperature, amount of cover and the population of mates. The gestation period for a litter is about twenty-one days with the average litter being three to five young. Each delivery takes four to five seconds with the female helping the young by pulling with her teeth. Older and larger females average more young per litter than other females. Once a captive pair had seventeen litters one year. One of their daughters had thirteen families, seventy-eight offspring.

When they are born the young are pink and hairless. Their eyes are closed, their ears are folded back against their heads and their weight is generally less than three-fourths of an ounce. At five days velvety fur appears on the backs of the young. In the next couple of days their teeth start coming in. When they are eight days old, their eyes open and their ears start to unfold. At two weeks the dull grey mice are weaned. The young are two inches long and weigh one ounce when they gradually change to adult coloring at eight to nine weeks old. They fully reach their adult size at three months. The life span of a meadow mouse in the wild is ten to sixteen months.

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The meadow mouse population varies from year to year. There is a fairly regular population cycle that reaches a peak every three or four years. When the population reaches these peaks, which are caused by longer breeding seasons, an increase in the number of young in a litter and more litters each season, the mice number may reach anywhere from sixty to 250 meadow mice per acre. During years of low population the number may be only fifteen to forty mice per acre. After the great abundance, and then collapse, there are only a few of the fittest left to start the next generation. There is also a super cycle when members may reach from 500 to 1,200 per acre. At such a time the whole population may attempt, to emigrate.

Detailed studies have been made of these cycles. One year at the peak of the cycle on Allen Tucker Prairie, a researcher set twelve traps in a field. When he walked around the traps in a circle, he had already caught one. In fifteen minutes he caught six meadow mice. The next year 100 traps set for ten nights caught only one mouse. These studies show that one year there can be many mice and the next they almost disappear.

Population cycles depend on a variety of factors. Some of these are natural parasites, abundance of food, predators and man's control. The parasites--mites, ticks, lice, fleas and worms--sometimes are more plentiful, cutting down the resistance of the mice. Fires, droughts, blights, sub-zero winters and other natural and man-made conditions bring a drop in food supplies.

Predators are a major factor in population cycles of the meadow mice. Their cycles and that of the mice and all wildlife interact. When the meadow mice are at a peak, then the predators have easy food and will be more numerous, as they depend more on this supply. Because of greater numbers of predators like owls, hawks, or coyotes, the mice population decreases and the predators in turn must change their diet from mice to other prey which may be more abundant. Also, as the decrease in mice starts, the decrease of the predator population starts. The predators start getting mange from malnutrition, parasites affect them more and their general health deteriorates.

Man is another factor in controlling population cycles. Clearing fields, or plowing them as Robert Burns did in his poem, destroys cover and stores for mice, leaving nests bare. Exposed to weather, predators and hunger, mice rarely survive. There are many other means man uses to cut the meadow mice population and protect his crops, such as encouraging predators like cats and dogs, setting out snap traps and poisons in orchards or hedges near cultivated fields, keeping vegetation Cut close to the ground near areas to be protected, and putting cinders or hardware cloth around individual trees to prevent mice from girdling trees.

With or without man's efforts at control, populations of meadow mice fluctuate from year to year according to the natural balance in which mice are an important link. More mice means more predators. More predators, less mice. Less mice, less predators. Less predators, more mice. Thinning the grass, working the soil and converting the nutrients the grass took from the soil to flesh and back to the soil to grow more grass, mice day after day demonstrate their importance in nature's life cycle.

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But watching us and cringing at our every movement, our mouse did not understand about nature's ways. All it knew was that it had no protection against our curiosity. To it we were no different from a hawk swooping down or a coyote pouncing on him, except, imprisoned in this strange box, we were the more terrifying, for it had no hole to escape through. In spite of our superior knowledge and our kindly intentions, in its prolonged state of shock and fear, it died. Like the poet, we disturbed natures plan--he, by destroying a mouse's nest by plowing it up in winter, and we, by taking a mouse from its nest. Both actions had the same results, and we also felt like Robert Burns when he wrote in 1785.

I'm truly sorry man's dominion
Has broken nature's social union,
And justifies that ill opinion
Which makes thee startle
At me, thy poor, earthborn companion,
An' fellow mortal!

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Copyright 1981 BITTERSWEET, INC.


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