Part 17

The most notable recent outbreak of this kind in the United States took place in the Humboldt Valley, Nevada, where, during the winters from 1906 to 1908, they swarmed over the cultivated parts of the valley and completely destroyed 18,000 acres of alfalfa, even devouring the roots of the plants. During this outbreak the mice in the alfalfa fields were estimated to number as high as 12,000 to the acre.

Whenever field mice become over-abundant notice appears to go out among their natural enemies, and in extraordinary numbers hawks, owls, crows, ravens, sea gulls, coyotes, foxes, bobcats, weasels, and other animals appear to prey upon them.

At no season of the year are they free from their foes, for they remain active throughout the winter, and most species apparently lay up no winter store of food. They travel to winter feeding places through series of tunnels under the snow, and it is mainly at this season that they do the most serious damage to orchards and shrubbery.

In the far North at the beginning of winter they gather in large numbers about the fur-trading stations and other habitations, where they persistently invade the food supplies.

Some of the northern mice, however, gather stores of food for winter. A species living along the coast of the Bering Sea and elsewhere on the Arctic tundra of Alaska accumulates a quart or more of little bulbous grass roots, which are delicious when boiled. They are hidden in nests of grass and moss among the surface vegetation, and before the first snowfall I have seen the Eskimo women searching for them by prodding likely places with a long stick. The roots thus taken from the mice are kept to be served as a delicacy to guests during winter festivals.

=THE PINE MOUSE= (=Pitymys pinetorum= and its relatives)

(_For illustration, see page 522_)

The pine mice form a small group of species peculiar to North America and closely related to the field mice. They are similar in form to the common field mice of the Eastern States, but are usually smaller, with much shorter tails and shorter, finer, and more glossy fur.

Most of the pine mice are limited to the wooded region of the States between the Atlantic coast and the eastern border of the Great Plains, and from the Hudson River valley and the border of the Great Lakes south to the Gulf coast. Strangely enough, one species lives in a restricted belt covered with tropical forest along the middle eastern slope of the Cordillera, which forms the eastern wall of the Mexican tableland, on the border between the States of Vera Cruz and Puebla.

Pine mice occupy the borders of thin forests and brushy areas, from which they work out into the open borderlands, especially in orchards or other places where there are scattered trees amid a rank growth of weeds. Instead of making their runways among growing vegetation on the surface of the ground like field mice, they live in little underground tunnels or burrows which extend in all directions through their haunts. These tunnels are closely like those of the common mole except that they are smaller and have frequent openings to the surface, through which the owners make short excursions for food. They often utilize the tunnels of moles when conveniently located for their purposes.

The tunnels are often so near the surface that the ground is slightly uplifted or broken as by a mole, or they are made under the fallen leaves and other small decaying vegetable matter covering the ground under the trees. Occasionally, when the surface soil becomes dry and hard, the burrows are deeper, so that no surface indications can be discovered. On account of the similarity of their burrows the depredations of pine mice are commonly attributed to moles.

Several inches below the surface pine mice excavate oval chambers to be used for nests or for storage purposes. The nest chambers have several entrances from ramifying tunnels and are filled with short fine pieces of grass, making a warm nest-ball. Here the several litters of young are born each year. Pine mice are less prolific than field mice, however, and the litters contain only from one to four young.

The food chambers are larger than the nest chambers, and when full of stores are kept closed with earth. In these are stored short sections of green or dry grasses, bulbous grass roots, and short sections of other edible roots. One such store contained about three quarts of the fleshy roots of a morning glory cut into short sections.

Pine mice obtain much of their food from the bark about the bases and roots of trees, including both coniferous and deciduous species. They kill many small trees and shrubs by girdling, or by cutting the roots below the surface, and in this way frequently inflict severe damage in orchards and nurseries. Owing to their underground habits they are much more dangerous to orchards than field mice. They also do much damage by burrowing along rows of potatoes and other root crops, upon which they feed.

Both pine mice and field mice are serious pests to agriculture and only by vigilant care can they be prevented from steadily reducing the returns from farm and orchard. A mouse appears so insignificant an enemy that the general inclination among farmers is to ignore it, but both field and pine mice exist in such enormous numbers and are so generally distributed that the aggregate annual losses from them are great.

Clean cultivation in orchards, especially for some distance immediately about the trees, is an excellent protective measure against both of these mice. The shrubbery and fruit trees of orchards, lawns, and gardens may be protected by the use of poisoned baits and traps as soon as signs of pine mice or field mice are observed.

=THE RED-BACKED MOUSE= (=Evotomys gapperi= and its relatives)

(_For illustration, see page 523_)

With the exception of the banded lemmings the red-backed mice are the most brightly colored of the smaller northern rodents. They are close relatives of the common field mice, which they about equal in size, but from which they are distinguished externally by rufous coloration, finer and more glossy pelage, larger ears, and proportionately longer tails.

The red-backed mice form a group containing a considerable number of species distributed throughout the northern circumpolar lands, except on the barren islands of the Arctic Sea. In North America they occur from the Arctic tundras north of the limit of trees southward throughout Alaska and Canada to the northern United States. With other northern species of mammals, birds, and plants they follow the high mountain ranges still farther southward to North Carolina, New Mexico, and middle California.

It is true that in the far North they are numerous on the moss-grown tundras, and in the South range above timber-line on high mountains. As a general rule, however, they are woodland animals, whether among the spruces, birches, and aspens of the North or farther south in the United States in the cool fir and aspen-clad slopes of mountains. They also frequent old, half-cleared fields, brush-grown or rocky areas, and similar places where cover is abundant.

Although so closely related to the field mice, the red-backed species are not known to become excessively abundant nor seriously to injure crops. One reason for their harmlessness in this respect may be their strong preference for forest haunts.

I once found them numerous in the grass-grown streets and yards of an abandoned mining camp in the forest at the head of Owens River, in the Sierra Nevada, of California. The mice were making free use of the congenial shelter afforded by the old log cabins, and their runways and entrances to burrows were all about under scattered boards and similar cover.

They are abroad equally by day and by night, and for this reason are better known to woodsmen than most of the small woodland animals. When foraging by day among the fallen leaves and deep green vegetation they present a most graceful and attractive sight, now moving about with quick and pretty ways, now pausing to sit up squirrel-like to eat some tid-bit held in the front paws and then on the alert to detect a suspected danger and poised in quivering readiness for instant flight.

Red-backed mice usually live in underground burrows similar to those of field mice, but generally located with more care in dry situations, the entrances sheltered by a stump, old log, root of a tree, rock, or other object. Ordinarily they do not make such well-defined runways as do many field mice, and sometimes no trace of a trail can be found leading away from their burrows. But where they travel about through small dense vegetation, under logs and about stumps and rocks they often make well-marked trails.

Their nests are bulky and formed of a mass of fine dry grass, moss, and other soft material, which is sometimes located in an underground chamber opening off the burrow and sometimes in hollow stumps and logs or under other surface shelters. But little is known about the home life of these mice except that they are prolific, and between April and October have several litters containing from three to eight young in each.

They feed upon a great variety of seeds, fruits, roots, and succulent vegetable matter and lay up stores for winter in underground chambers or in hollow logs and similar places above ground.

With the coming of winter they gather about cabins and other habitations in their territory and become as persistent as house mice in searching out and raiding food supplies of all kinds. When the more appreciated kinds of food fail they resort to gnawing the bark from roots and bases of trunks of small deciduous trees of various kinds.

During my sledge journeys in the region about Bering Strait I found the skins of many red-backed mice among the Eskimo children. The small boys kept them with lemming skins as evidences of their prowess with miniature dead-fall traps and blunt-pointed arrows, and the little girls kept them as prized robes for the dolls carved by their fathers from wood or walrus ivory.

=THE RUFOUS TREE MOUSE= (=Phenacomys longicaudus= and its relatives)

(_For illustration, see page 523_)

The genus Phenacomys, to which the rufous tree mouse belongs, includes a number of species closely similar in size and external appearance to some of the well-known field mice. The structure of their teeth, however, shows that they form a distinct group of animals.

So far as known, the living members of the genus are confined to the Boreal parts of North America, where they range from the Atlantic to the Pacific in Canada, and southward along the mountains to New Hampshire, New Mexico, and northern California. The discovery of fossil representatives of the genus in Hungary and England indicates that it was formerly circumpolar in distribution.

All but one species of the genus live on the ground, inhabit burrows, make runways through the small vegetation, and feed on grasses and other herbage--all in close conformity with the habits of the meadow mice.

The tree mouse, however, is a strongly aberrant member of the group. It differs from all the others, and from all field mice, not only in its rufous color and longer tail, but in its remarkable mode of life. It is restricted to the humid region of magnificent forests in western Oregon and northwestern California, where it often spends its life in the tops of such noble trees as the Sitka spruce, the Douglas fir, and the coast redwood. Such an amazing departure from the habits of its kind lends unusual interest to this little animal.

Its nests are generally located high up in the trees, sometimes 100 feet from the ground, in forests where the branches of neighboring trees interlace so that it can pass from one to another and inhabit a world of its own, free from the ordinary four-footed enemies which prowl below.

The nests vary in size, structure, and location. In Oregon they have been found only in large trees at elevations varying from 30 to 100 feet. On the seashore near Eureka, California, they are placed on the branches of small second-growth myrtle and redwood trees. Farther inland in the same region many are in small trees, within a few yards of the ground, on the border of heavy redwood forests.

The higher nests of the tree mice are often the deserted and remodeled homes of the big gray tree squirrel of that region (_Sciurus griseus_) and contain a foundation of coarser sticks than in the nests wholly built by the mice. The larger proportion of the nests are built by the mice and are usually composed of small twigs, fragments of a netlike lichen, skeletons of fir, spruce, or other coniferous leaves, and the droppings of the mice themselves. They vary from small oval structures a few inches in diameter, located well out on the branches, to great masses close against and sometimes entirely surrounding the tree trunks, supported on several branches, and measuring three feet long and two or three feet high.

The interior of these large structures is pierced with numerous passageways and sometimes as many as five separate nest chambers are scattered through one. Tunnels run out along each of the limbs on which the mass rests, and if it extends all the way round one main tunnel encircles the trunk from which these hallways branch.

Such great nests have evidently been used for a long period and have grown with the steady accumulation of material. This has gradually decayed and become a solid mass of earthy humus. The large nests are usually the abodes of a single female, the homes of the males having been found to be small and more often located away from the trunk of the tree. The food of the red tree mouse, so far as known, consists entirely of the fleshy parts of fir and spruce needles and the bark from coniferous twigs.

Tree mice appear to breed throughout most of the year and have from one to four young in a litter. They are mainly nocturnal, and when driven from their nests by day appear rather slow and uncertain in their movements. Those living in highly placed nests usually escape by running out on the limbs, and pass from one tree to another if necessary. Those in small trees usually drop quickly from limb to limb until they reach the ground, when they run to the nearest shelter.

That these mice sometimes descend to the ground of their own volition is probable, but the fact that the stomach of every individual so far examined has contained only the fleshy parts of coniferous leaves indicate that their food habits have become so fixed as to make arboreal life a necessity.

The modification of the habits of a member of a group of ground-frequenting animals, with a structure adapted to such an existence, to those of a strictly arboreal animal is so strange as to make the question of cause a puzzling one.

In the Hawaiian Islands the introduction of the mongoose has made the common house rat arboreal in habits, and possibly in the remote past the pressure of some ground-frequenting enemy thus affected the lives of the red tree mouse. An animal rarely makes an abrupt change in its habits without direct pressure from some source, and then only as a matter of self-preservation.

=THE MUSKRAT= (=Fiber zibethicus= and its relatives)

(_For illustration, see page 526_)

The muskrat, or “musquash,” as it is widely known in the northern fur country, is three or four times the size of the common house rat, to which it bears a superficial resemblance. It has a compactly formed body, short legs, and strong hind feet partly webbed and otherwise modified for swimming. The long, nearly naked, and scaly tail is strongly flattened vertically and in the water serves well as a rudder. The fur is nearly as fine and dense as that of the beaver and, as in that animal, protects its owner from the cold water in which so much of its life is spent.

Muskrats are peculiar to North America, where they exist in great numbers. Aquatic in habits, they have a wide distribution along streams of all sizes and among marshes, ponds, and lakes from the Atlantic to the Pacific, and from a little beyond the limit of trees on the Arctic barrens south throughout most of the United States. They reach our southern border at the delta of the Mississippi and the delta of the Colorado, at the head of the Gulf of California.

Within this vast area they have been modified by their environment into several species and geographic races, none of which differ much in appearance from the well-known animal of the Eastern States.

The nearest kin of the muskrats are the short-tailed field mice, so numerous in our damp meadows. Like the latter, the muskrat has several litters of young each season. The young are born blind, naked, and helpless, and number from three to thirteen to a litter. This great fecundity has enabled the muskrats to hold their own through years of persistent trapping.

They still occupy practically all their original range and yield a steady toll of valuable fur each season. In 1914 more than 10,000,000 of their skins were sold in London, and other millions were handled in America. The aggregate returns on muskrat skins are so great as to constitute it our most valuable fur-bearer. The furriers make its skins up in its natural color or dress and dye it and give it the trade names of “Hudson seal,” “river mink,” or “ondatra mink.”

In suitable marshes, as on the eastern shore of Maryland, muskrats become extremely abundant and render such areas valuable as natural “fur farms.” One Maryland marsh containing 1,300 acres has yielded from $2,000 to $7,000 worth of skins a year. Not only are the skins of value, but the flesh is palatable, and is sold readily under the trade name of “marsh rabbit” in the markets of Baltimore, Philadelphia, and elsewhere.

There is little doubt that owners of favorably situated marshes could derive from them a steady revenue by keeping them stocked with proper food plants and protecting the muskrats from their enemies. The value of these fur-bearers is becoming more and more appreciated and many States have laws restricting the trapping season to a period in fall and winter when the fur is prime.

In marshes about shallow lakes or bordering sluggish rivers muskrats build roughly conical lodges or “houses,” three to four feet high, with bases, usually in shallow water, several feet broader. These houses are made of roots and stems of plants with a mixture of mud. An oval chamber is left in the interior, well above the water level, to which entrance is gained by one or more passageways opening under water. These shelters are mainly for winter use, but the young are sometimes born in them as well as in large grass nests among dense marsh vegetation.

The curious conical lodges are familiar objects about marshes in the Eastern and Northern States, and I remember seeing, a few years ago, a specially well-formed muskrat house close to the historic bridge, at Concord, and others along the Concord River. Within ten years muskrat houses were common in marshy ponds in Potomac Park, Washington, where the Lincoln Memorial Building now stands.

Where the banks of streams or lakes rise abruptly, the muskrats make their home in dry chambers in the banks above water level at the end of a tunnel opening either under water or close to the water level. Worn trails lead up the banks about such places and well-marked runways are made through the heavy reeds and marsh grasses in their haunts.

Muskrats are mainly nocturnal animals, but often move about during the day. I have seen them repeatedly swimming close to the bank of the Potomac a short distance above Washington. They like to carry their food to slightly elevated points where they can overlook the water along shore, such as the top of a projecting log, large stone, or earthen bank, from which they plunge headlong at the first alarm. Many a solitary canoeman gliding silently along the shore of stream or pond at night has been startled by the disproportionately loud splash made by a muskrat diving from its resting place.

Their food consists mainly of the roots and stems of succulent plants varied with fresh-water clams, an occasional fish, and even by cultivated vegetables grown in places readily accessible from their haunts. They store up roots and other vegetable matter for winter use and remain active throughout that season. The roots of which their “houses” are built are frequently those used for food and sometimes serve as winter supplies.

As a rule, muskrats keep near their homes in winter, making excursions here and there beneath the ice. Sometimes the water rises and forces them out and they wander widely in search of new locations. When encountered at such times they show extraordinary courage and fiercely attack man or beast. The first muskrat I ever saw was one which a farmer met in midwinter in a snowy road in northern New York. As soon as the man drew near, the animal rushed at him with bared teeth and fought savagely until killed.

Muskrats are usually harmless animals and their presence in marshes and along watercourses lends a pleasant touch of primitive wildness to the most commonplace situations. They appear to have so adapted their habits to the presence of men that they go on with their affairs with curious indifference to their human neighbors. In irrigated country or elsewhere where banked ditches are built their habits render them serious pests, as their burrows and tunnels drain ponds or cause destructive washouts.

An interesting chapter in the history of these animals began in 1905, when four Canadian muskrats were introduced on a nobleman’s estate in Bohemia. Since then they have increased rapidly and spread over a large area in Bohemia and beyond its borders. The streams in the region they occupy are controlled by grassy banks, and dams are built to form ponds for fish culture, which is a large industry there. The muskrats persistently tunnel into the banks and dams, causing them to give way, thus causing heavy losses to the owners.

They also work havoc among river crabs and mussels, which have great economic value, and interfere with the fish and their spawning beds. To cap the climax of their misdeeds, they are reported to feed on grain and vegetables and to destroy the eggs of domestic poultry and of wild-fowl. It is reported also that these expatriates in their foreign environment have become larger animals than their ancestors, and that their fur has greatly deteriorated in quality. The measures prescribed by the Agricultural Council of the Kingdom of Bohemia for their control are apparently without much success. This instance is a good illustration of the danger attending the introduction of an animal from its native habitat into a new region.

=THE WOODRAT= (=Neotoma albigula= and its relatives)

(_For illustration, see page 526_)