THE GNAWERS
The great order Rodentia--rats, mice, rabbits, porcupines, squirrels,
beavers, etc., derives its name from the Latin verb _rodere_, to gnaw,
or eat away (something), and is characterized by the great development
of the front (incisor) teeth, by means of which rodents get their
living by biting off, or gnawing through, the plants and woody stems
on which they feed, or which they use in constructing their dwellings.
All are primarily vegetable eaters, yet none will refuse a meal of
flesh when opportunity offers to get it, and some are decidedly
carnivorous, especially as to fish. They are distributed all over the
world, including the Australian region. They are chiefly terrestrial,
and often burrow or live in ready-made burrows. Some are aquatic, such
as the voles; others, like the squirrels, are arboreal. In perhaps
a majority of the forms the hind legs are much longer and stronger
than the forelegs, giving the animals great leaping power, while the
forefeet, with their long and flexible fingers, are constantly used
as hands. Many are beautifully marked in varied tints of gray, brown,
red, and black, so that their pelts have value in the fur market;
and their flesh is an important element in human food. On the other
hand the activity of these animals, when numerous, causes serious
damage to gardens, crops and orchards and one of them, the rat, is
unquestionably the most dangerous animal to human health and prosperity
in the whole animal kingdom. The fecundity of the smaller, murine
species, is great, and from time to time they increase inordinately in
favorable places, and swarm abroad in vast and destructive migrations.
Were it not for the fact that the rodents furnish the principal part
of the food of predatory mammals, reptiles, and birds, and are thus
kept down, the globe would soon become so populous with this tribe that
hardly anything else could maintain existence.
The distinguishing anatomical characteristic of the rodents is the
dentition. The canines, so essential to carnivorous, predatory animals,
are here completely absent, and a long empty space intervenes between
the incisors and the molars, or cheek teeth, which vary greatly in
number and form among the different families. The incisors consist
of a single pair in each jaw, very large and strong, and composed of
vasodentine, _faced only_ with hard enamel, often yellow or red. As the
softer substance behind the facing wears away more easily, the incisor
takes a chisel shape, leaving the hard enamel in front projecting
slightly as a cutting edge; thus these teeth always remain sharp. The
rodents are traced back in their lineage to the order Tillodontia of
Eocene time. The oldest family of modern type in the order is that of
the squirrels.
Let us begin with the rabbits and hares (family Leporidæ). The name
properly applies to the Old World species _Lepus cuniculus_, the
burrowing wild rabbit from which all our various domestic rabbits are
descended, whose special characteristic is the fact that they live
in holes in the ground of their own digging, and in large colonies
called warrens. All the other species make their breeding beds and
resting places on the surface of the ground, in the best concealment
(outside of forests) that they can find. Such a home is called the
animal's "form," and when it contains a litter of young the mother
covers them with a blanket of hair which at that season she is shedding
copiously. Strictly speaking, all the Leporidæ, except the _cuniculus_,
are "hares"; but the general term "rabbit" is now so common that the
scientific distinction is of no consequence. Europe and Asia have
two kinds of hares, and several exist in this country, such as the
familiar "cottontail" or bush rabbit of the east, the southern swamp
rabbit, and several species of large, long-eared, swift-footed hares
of the western plains called "jack rabbits." The most important one,
however, is the large northern one named "snowshoe rabbit," because
in winter it receives a broad growth of hair on the feet, aiding it
in traveling over the snow. This rabbit turns white in winter, the
hairs losing their color with the advent of cold, as also does the big
arctic hare which wanders as far north as land extends. These northern
hares are the chief dependence for food in winter of all the Canadian
fur-bearing animals, and indirectly of the native Indians. Consequently
when, as happens at intervals of a few years, the rabbits of a
district all but wholly die off by an epidemic, a famine and dreadful
distress occurs--or used to when civilized aid was less available than
now--in northern Canada, and the commercial outcome of furs is greatly
diminished.
As the hares feed on herbage and bark, obtainable all the year round,
they are abroad in winter; but they have a family of small cousins, the
pikas (Lagomyidæ) that inhabit our western mountain tops above timber
line and must hibernate. Other species abound in the Himalayas. They
are little, short-eared, tailless creatures that make their homes in
companies among loose rocks, and store in their deep crevices enough
dried grass and flowering plants to keep themselves alive until the
late spring of those cold heights. Western folks call them conies.
The porcupines are large, plantigrade rodents notable for the mixture
of quill-like spines with the hair. This is most conspicuous in the
European species, which bristles with spines reaching far beyond the
hips and concealing the tail, forming an excellent defensive armor.
Some smaller African and East Indian species are less well armed, and
have longer tails, at the end of which are tufts of spines, making
an effective weapon. All of these pass their time and get their food
on the ground. Our American porcupines (family Cercolabidæ) differ
somewhat anatomically and live for the most part in trees, although
our common eastern porcupine wanders about a great deal in summer,
especially at night, feeding on herbage, and rejoicing in a find of
bones or other saline food here and there. It is defended by a coat of
long black hair in which spines are plentifully mingled, and the short,
flat tail, covered with thick spines, may give a sidewise stroke that
makes man or beast cautious about attacking an animal that otherwise
seems so lethargic and helpless. The porcupines of this family,
however, really belong to trees, where they slowly consume the foliage
and tender bark, and remain quietly through even Canadian winters. The
Pacific side of the country has a similar species in the yellow-haired
porcupine; and several smaller kinds exist in Central and South
America with scanty spines and long prehensile tails.
Closely allied to the porcupines are the gregarious viscachas of the
South American plains, that live in "villages" of burrows, and much
resemble prairie dogs in appearance and habits; also the chinchillas of
the high levels of the Andes, whose soft gray coat is one of the prizes
of the furrier. Here, too, come the swift-footed, slender agoutis and
pacas of South America, many species of which exist and are useful as
food; and a neighboring family contains the little cavies, from one of
which are derived our pet "guinea pigs," which are not pigs and do not
come from Guinea; also their cousin, the almost aquatic capybara, which
measures three feet long, and so is the biggest known rodent. This is
much hunted for its flesh, and is the principal prey of the jaguar.
This brings us to the world-wide tribe of rats and mice formed by
a group of eight families, of which the typical one (Muridæ) alone
contains a third of all Rodentia, and the other seven creatures
differing greatly from these familiar models. Many are small, such as
the house mouse (originally a native of southeastern Asia, as also
were the rats that commerce has carried all over the civilized globe),
and the even tinier harvest mice, gray or brown in plain color, and
with long, slender and nearly hairless tails and legs fairly equal in
size. Thence in size they grade up to the stature of the rat, and from
that on to the South African "springhaas" which is as big as a rabbit,
and to our muskrat, two feet long, counting in its tail. Although
essentially alike in structure some have varied widely from the
ordinary type. Thus the jerboas, several species of which inhabit the
plains of Asia and Africa, have the hind legs so long that their bones
are considerably longer than the distance from the root of the tail to
the nose; and they progress in long rapid leaps, balancing themselves
by long tails, often tufted at the end. The big "jumping hare" of
South Africa has much the appearance of a kangaroo with a squirrellike
tail; and a genus of exquisitely dressed mice in our sandy Southwest
are called "kangaroo" mice. In fact one of our commonest reddish field
mice, found all over the country, has similar proportions, and is
remarkable for its long leaps when hurried.
A shortening of the tail is seen in the voles, to which the common
meadow mice of various species belong, and still more in the lemmings,
in the Old World mole rats, and in our pouched gophers. All these are
not only ground-keeping kinds, but burrowers, and have no use for a
long tail, save in the case of the muskrat, which is really a big vole
that has taken to an aquatic life, and needs an oar to scull himself
through the water; for muskrats swim more by means of their tails than
by their feet. The foremost burrowers are the pouched gophers, whose
long tunnels, and food-getting, do so much damage to crops in the
central plains region of this country. They must be distinguished from
the ground squirrels, also called "gophers."
An interesting diversity of habits may be met with here. Some rodents
live in deeply excavated burrows, others in shallow diggings or holes
in stumps and rock crevices; some, like the water voles, reside in
holes in the banks of streams, or, like the muskrat, heap up "houses"
in a marsh in which to pass the winter in security; while still others
construct ball-like nests among the herbage, or in bushes and trees.
Some truly hibernate in cold countries, like the famous dormice of
Europe, and our equally sound sleeper, the American jumping mouse;
but mostly they stay in snug habitations and live through the winter
on collections of food, or, like field mice, gather seeds abroad even
in the coldest weather, or poke about under the snow for food, as do
the lemmings. From time to time certain species, especially of the
short-tailed field mice and the lemmings, multiply excessively in some
district, and then are forced to spread away from their birthplace in
those migrations of myriads which form the "plagues" that devastate
large tracts of country. They march on until an accumulation of enemies
and an epidemic of illness combine to kill them off.
SQUIRRELS, WOODCHUCKS AND BEAVERS
Squirrels in form and activities are much alike all over the world,
and are absent only from Australia and Madagascar. The long, bushy
tail that makes so excellent a blanket as it is wrapped about their
bodies when curled up asleep, is the badge and pride of the tribe. They
inhabit hollows in the trees or sometimes holes among their roots, and
in summer make globular nests of leaves and twigs in which the young
are nursed and trained. Nuts form their staple food, but berries,
fruits, roots, funguses, insect grubs, etc., offer changes in fare
with the recurring seasons. Sometimes great ingenuity is displayed in
getting at this food. Some species are arrant robbers of birds' nests,
and now and then kill and eat small birds and mammals; and the older
males are resolutely kept away from their babies by the mothers for
fear of cannibalism. This catholic appetite, and their willingness to
wander from place to place in search of things seasonable, enable
squirrels to find food of some sort every month of the year, yet most
species have the forethought to lay up in more or less secret places
a winter supply of provender; consequently no species of Sciurus
hibernates, strictly speaking.
This storing of winter provender is a matter that has been regarded
with more general interest, perhaps, than any other feature of animal
economy, and is mainly manifested among the rodents, although practiced
in a limited way by some others, as for instance, by weasels and foxes.
It looks like conscious foresight of the famine time to come, but it
is no doubt in the main, if not wholly, instinctive, since the young,
who have had no experience of the winter's scarcity or imprisonment
ahead, make suitable preparations. It seems to me that this habit,
so necessary to the existence of small, vegetarian creatures in cold
climates, arose in some such way as this:
The little animals that store supplies designed to keep them alive
through the winter are those whose food is for one reason or another
unobtainable then. Remember, also, that they are feebly endowed with
powers either for defense or for escape outside their homes, and when
gathering their food must not loiter much to eat as they go, but must
pick up what they can carry and hasten to the safety of their doorways.
This is the reason why surviving species of such animals have acquired
cheek pouches, in which they can transport a fair meal of their food to
be eaten at home at leisure.
During the larger part of the year food is scant, and these rodents
get into the way of picking up every bit they can find, and seem so
restless and energetic that some of them, such as the viscachas and
pack rats, accumulate about their burrows or nests quantities of
inedible things, moved, apparently, by mere objectless acquisitiveness.
The search for food, the foremost occupation and anxiety of these small
wood-folk, would be increasingly stimulated as the ripening season of
the seeds and nuts on which they depend advanced, and the impulse to
incessant industry, so necessary in the poorer parts of the year, would
now be overworked, and each animal, in his haste to be up and doing,
would constantly bring home more food than would be consumed, so that
it would pile up in the accustomed "dining room." The gradual failure
of outdoor supplies, as winter came on, would lead to the eating, with
increasing frequency, of those fragments casually saved in and about
the burrow or house, which, from their nature, would not have decayed.
The animal which had been most busy and clever in food gathering would
own the largest amount of the leavings of these autumnal feasts. Having
the most food he would be among those of the colony or neighborhood
strongest and most likely to survive, and to give to his offspring the
tendency to strength and industry which had been his salvation. This
would be continued and shaped by the process of natural selection into
a valuable, instinctive habit of gathering nonperishable food in large
quantities every autumn, and thus providing themselves with stores
to last through the coming winter; but it does not follow that the
squirrels and mice are conscious of this wise forethought.
The striped, chattering, ever-busy chipmunks, of which America
possesses several delightful species, although able to ascend into
trees, and frequently doing so, are groundlings, and fond of rocky
places into whose crevices they can quickly rush when an enemy is seen
or heard; hence their fondness for the stone walls that in the East
divide farm fields, and in general they are more inclined to associate
with man and his works than are the tree squirrels, although the grays
lend themselves readily to the semidomestication of residence in
village streets and city parks, as the red never does. The chipmunks
dig long underground tunnels, enlarged here and there into chambers
serving as bedrooms, storerooms for food, and refuse bins; and the
northwestern species are so numerous that between what they eat and
waste in gardens and grainfields and the bad runways for water their
galleries make, they are justly regarded as a pest.
These pretty but troublesome chipmunks are called "gophers" in some
parts of the West, but that name is more generally given to the gray or
brownish ground squirrels of the plains, classified as spermophiles by
naturalists; and they are so varied, numerous and destructive wherever
grain is grown, from the prairies of Kansas and Nebraska to the
California valleys, and northward to the Saskatchewan, that extensive
and costly poisoning operations are necessary to suppress them. Similar
to them, but larger, are the prairie dogs, whose communities, or
towns, of burrows and tunnels render useless large tracts of land in
the southern half of the plains. Very similar animals to these abound
in Russia and eastward throughout the open country of central Asia.
They have undoubtedly increased much within late years through the
killing off of the natural enemies that in the old days held their
multiplication in check.
The prairie dogs used to be called "marmots," a term that applies
more properly to some larger European burrowing rodents and to our
woodchucks, which are so common all over the eastern half of the
country, and, in another species, on the summits of the northern
Rockies, where they are known as "whistlers." The most remarkable
thing about them is the length and intensity of their dormancy in
hibernation. There remains only the beaver, the largest of the rodents
except the capybara, and altogether the most important one, measured
by the value of its fur, and by the service its race has done through
thousands of years in preparing, by its clearings and dams, valleys for
man's cultivation.
Every beaver settlement is a true colony, the offspring of some
previous settlement, which may be hundreds of years old. When such a
settlement becomes too populous for the food supply, young males and
their mates travel to some fresh spot by a small woodland stream, and
begin life by digging a burrow in the bank with an underwater entrance,
and at once dam up the stream by piling sticks, sod and mud across
its current at some favorable spot below their home, the effect, if
not the conscious purpose, of which is to maintain a depth of water
in the stream at all seasons sufficient to cover the entrance to the
burrow, and also to permit the storage of green wood under water (and
ice) near the home for food (they eat the bark) during the next winter.
The young beavers born that season will remain through the winter
with the parents, and a domelike house is usually built in which the
family lives. Next season the young set up a home for themselves near
by, and so the colony grows. Beavers get most of their food by cutting
down trees other than evergreens, and gnawing the bark. As the trees
disappear near the bank, and the colony increases, the dam is enlarged
so as to spread the set-back water over a wider territory; and later
canals are cut deep into the woods, permitting far-away trees to be
felled, and their pieces floated to the houses, especially in gathering
the supply for winter. Old dams are sometimes 100 or more yards long,
and are built with astonishing intelligence with reference to holding
back a great breadth of water. These are diligently and skillfully
repaired; and the houses become, in the course of years, big enough to
accommodate three generations of beavers at once, and are so massive,
especially when frozen in winter, which is the time of most danger from
their enemies, that they are practically safe from attack. From such a
mature colony others are continually formed, until in a level, swampy
region the whole district is well occupied by beavers. This is possible
now, of course, only in the remote Northwest; but a few beavers survive
in the Rocky Mountain region of the United States, under protective
laws, and they are still numerous in the more thinly settled parts of
Canada, and furnish a large return to trappers.