BEAVERS AND THEIR WORK—THE DAM AND THE POND—PRACTICE WITHOUT
PRINCIPLES—A USEFUL TAIL—HOW BEAVERS CUT DOWN TREES.
The beaver may be said to occupy amongst mammals the place that ants do
amongst insects. Wood says of him: “Of the Social Mammalia, he takes
the first rank, and is the best possible type of that group. There are
other social animals, such as the various marmots and others; but these
creatures live independently of each other, and are only drawn together
by the attraction of some favourable locality. The beavers, on the other
hand, are not only social by dwelling near each other, but by joining in
a work which is intended for the benefit of the community.” As everyone
knows, the beaver is an aquatic animal, as is sufficiently indicated by
his appearance. He has a dense, woolly coat, which, as in the case of the
otter and the still more water-loving seals, is protected by an outer
covering of long, smooth hairs, which are of a reddish brown colour.
The toes of the hind feet are webbed, whilst the tail is broadened out
into the shape of a paddle, the blade of which, however, lies flat on
the water, so that it is not used by the animal as we would use a scull
or a paddle, but with an upward and downward motion. When the beaver
moves his tail laterally—that is to say from side to side—as he is very
well able to do, it cuts the water, after the manner and with the same
effect that a scull does when worked by a seaman at the stem of the boat,
instead of in the rowlocks as we use it.
[Illustration: OTTER AND SALMON.]
This tail of the beaver is a very wonderful organ, and by far the most
conspicuous feature about the animal. The late Mr. Morgan, who made a
study of beavers and their habitations, says of it: “It is nearly flat,
and covered with horny scales of a lustrous black. These scales, which
are such in appearance only, cover every portion of the surface, both
above and underneath. Its principal uses are to elevate or depress the
head, while swimming, to turn the body and vary its direction, and
to assist the animal in diving. It is also used to give a signal of
alarm to its mates. When alarmed in his pond, particularly at night,
he immediately dives, in doing which the posterior part of his body
is thrown out of water, and as he descends head foremost, the tail is
brought down upon the surface of the water, with a heavy stroke, and deep
below it with a plunge. The violence of the blow is shown by the spray,
which is thrown up two or three feet high.”
Elsewhere the same authority says: “Whilst watching upon their dams
at night I have been startled by this tremendous stroke, which, in
the stillness of the hour, seemed like a pistol-shot. I have heard it
distinctly for half a mile, and think it can be heard twice or three
times that distance, under favourable conditions.” That must have been a
splendid thing to hear—that sudden, startling blow—in the dead silence of
the night, and in the loneliness of the North American wilderness; in the
Hudson’s Bay territories perhaps—the headquarters of the beaver—where,
for hundreds of miles around, there would be no other white man, or even,
perhaps, an Indian, within a very great distance. Any other beaver that
happened to be about at the time—at any rate, all those that were living
in the same pond—when they heard that sound of alarm would go down too in
the same way, so that there would be cracks like pistol-shots all about.
That would be a concert worth listening to.
But now, what is this pond of the beavers which is referred to by Mr.
Morgan in the above passage of his book, _The American Beaver and his
Works_—a most interesting work, which should be read by anyone who wants
to know all about beavers? It is made, or rather caused, by the beavers
themselves, and this brings us to the dam, which is their principal
work, and which they construct for the express purpose of having this
pond to live in. They are animals who simply cannot do without water,
and as the streams on which they take up their abode are often small
and shallow, it is of the greatest consequence to them that they should
never run dry—which in a drought or dry summer they might easily do.
To prevent this, having first selected a part of the stream where the
water is not more than two or three feet deep, they bring earth from the
adjacent banks and lay it down in mid-stream. Soft earth of a clayey
consistency is preferred, for this, penetrated as it is, and partially
held together, by roots and other vegetable fibres, is not at once washed
away by the force of the water. The beavers have thus time to add to and
strengthen the dam, and the better to effect this object they lay sticks
and brushwood upon it, which they then press down into the mud with their
feet. To these stones are added, and then more earth and sticks, till at
last the crest of the dam appears above the surface of the water, and
begins to rise higher and higher. It may attain, at last, to a height of
six feet, or even more, above the level of the stream, whilst the length
of some dams is as much as two hundred, or even three hundred feet.
The stream itself, at the point where the dam intersects it, may only
be a few yards in breadth, but as the mass of the flowing water cannot
penetrate the solid embankment of mud and sticks which the beavers have
made, it broadens out and begins to make a way on either side of it.
The beavers, however, to prevent this, keep lengthening the dam, and in
this way, as the stream can no longer flow in its channel, and can only
get by the obstacle placed in its way, very slowly, by spreading out and
flooding the surrounding country, the result is that a great pond or
basin of water is formed on the up-stream side of the dam, and this the
beavers have all to themselves. Of course, when the water is checked in
its flow, it begins to rise against the dam that confines it, and as only
a small quantity percolates through, it sinks and runs away in a much
smaller volume, on the other side of the obstruction. When a flour-mill,
which is to be worked by water-power, is erected by the side of one of
our small streams, exactly the same principle is employed, a dam being
built across it, from bank to bank, and the water running off by a
side-channel.
Beavers, however, existed long before there were any millers, and
moreover, they make better dams than our millers do, or, at least, they
construct them upon more scientific principles. The mill-dam runs, as a
rule, straight across the stream, but the beavers curve theirs a little
up into it, so that the water does not rush against it so violently as
it would if it were straight, but flows smoothly off upon either side.
This is how we make our sea-dams—at least when it is possible—and where
any structure has to resist a great force of water, as, for instance,
the buttresses of a bridge across some large river, it is always shaped
like this, only more so; that is to say, we turn the curve into an acute
angle and present a sharp edge, instead of a rounded surface, to the
impetuous rush of the stream. In this way the water is cut in two, as if
by a knife-blade, whereas, if the masonry presented a broad surface for
it to rush against, the first flood might wash the strongest bridge away.
Practical experience seems to have led to the beaver’s employment of the
principle, though probably he has no very clear ideas as to what the
principle is. He could not “formulate it”—as we say—and to say the truth,
neither could I myself at this moment.
Besides the first, or great dam, the beaver sometimes makes a smaller one
lower down the stream. This smaller dam is perhaps a more interesting
structure even than the principal one, from the point of view of the
beaver’s intelligence. The pond which is formed above it by the now
diminished stream, is too small to be of much use to the animal, but by
increasing the height of the water behind the great dam, it diminishes
the pressure of the stream against it, on the other side, so that there
is less fear of the dams bursting. This, too, is by a principle which
I should find it difficult to formulate myself—and it can hardly be
supposed that the beaver knows anything about it. The surprising thing is
that, somehow, practically, he has found it out—that is to say, he knows
how to apply it, without having any idea of what he is doing. In carrying
the mud and sticks to the water, the beaver walks, it would seem, upon
his hind legs, and in placing and working them together, he generally
also assumes the upright attitude. The massive tail, by acting as a base
or fulcrum, on which the animal can lean back, enables it to do this
with the greatest ease. The toes of the forefeet are not webbed, as are
those of the hind ones, nor do they aid in swimming, being then pressed
against the body, but are used more as hands, at least for the purposes
of architecture. With them the beaver scoops up the mud, and holding it
between them or pressed against his throat, walks upright to his dam
like a little mannikin in a brown fur coat. It used to be thought that
the broad, naked tail served the beaver as a trowel, for the laying and
plastering of the mud. This was not so entirely an error as one generally
reads it is, since Mr. Morgan tells us that “he uses his tail to pack
and compress mud and earth, while constructing a lodge or dam, which he
effects by heavy and repeated down-strokes,” and he adds, truly enough,
“that it performs, in this respect, a most important office, and one not
unlike some of the uses of the trowel.” This shows that there was really
something in the old idea, but it was imagined also that the beaver,
besides using his tail as a trowel, actually prepared mortar with it,
from mud. This was a fable, but there was much more truth in the general
statement, of which this was only an item, than in the learned _ex
cathedrâ_ denial, which denied everything—and so it very often is. As we
have seen, both wood and mud enter into the construction of the beaver’s
dam, besides stones, which do not play so important a part. I have called
the wood “sticks” because that is the word usually employed in America,
where beaver-dams are often called “stick-dams.” But these sticks may be
of a considerable size, so that we should often rather call them logs,
or, at any rate, branches. Branches, gnawed into various lengths, is what
they really are, and to obtain them the beaver, which is a rodent, and
armed with two enormous chisel-like teeth in each jaw, is accustomed to
cut down trees, often of a surprising size, when its own is taken into
consideration.
Two or more beavers—according to Mr. Morgan—generally assist in the
cutting down of a tree. “Although,” he says, “I have not succeeded in
witnessing the act, I have obtained the particulars from Indians and
trappers who have. The usual number engaged in the work is but two of a
pair; but they are sometimes assisted by two or three young beavers. It
thus appears to be the separate work of a family, instead of the joint
work of several families. When but two are engaged they work by turns,
and alternately stand on the watch, as is the well-known practice of
many animals while feeding or at work. When the tree begins to crackle
they desist from cutting, which they afterwards continue with caution
until it begins to fall, when they plunge into the pond, usually, and
wait concealed for a time, as if fearful that the crashing noise of the
tree-fall might attract some enemy to the place. The next movement is
to cut off the limbs, such as are from two to five and six inches in
diameter, and reduce them to a proper length, to be moved to the water
and transported thence to the vicinity of their lodges, where they are
sunk in a pile as their store of winter provisions. Upon this work the
whole family engage with the most persevering industry, and follow it up,
night after night, till the work is accomplished.”