RODENTS.
THE rodents, psychologically considered, are, of all orders in the
animal kingdom, most remarkable for the differences presented by
constituent species. For while the group contains many animals, such as
the guinea-pig, whose instincts and intelligence cannot be said to rise
above the lowest level that obtains among mammalian forms, it also
contains other animals with instincts as remarkable as those of the
squirrel, intelligence as considerable as that of the rat, and a
psychological development as unique as that of the beaver. In no other
group of animals do we meet with nearly so striking an exemplification
of the truth that zoological or structural affinity is only related in a
most loose and general way to psychological or mental similarity. Up to
a certain point, however, even here we meet with an exemplification of
what I may call a complementary truth, namely, that similarity of
organisation and environment is in a general way related to similarity
of instincts (though not necessarily of intelligence). This is obviously
the case with the habit from which the order takes its name; for whether
the instinct of gnawing is here the cause or the result of peculiar
organisation, the instinct is unquestionably correlated with the
peculiarity. And similarly, though less obviously, is this the case with
the instinct of storing food for winter consumption, which is more
prevalent among the rodents than in any other order of mammals--rats,
mice, squirrels, harvesters, beavers, &c., all manifesting it with
remarkable vigour and persistency. Here we probably have a case of
similar organisation and environment determining the same instinct; for
the latter is not of sufficiently general occurrence among all species
of rodents to allow us to suppose that the species in which it does
occur have derived it from a common ancestry.
_Rabbit._
Rabbits are somewhat stupid animals, exhibiting but small resources
under novel circumstances, although inheriting several clever instincts,
such as that of rapidly deciding upon the alternative of flight or
crouching, which is usually done with the best judgment. I have,
however, often observed that the animal does not seem to have sense
enough to regard the colour of the surface on which it crouches, so that
if this happens to be inappropriate, the rabbit may become conspicuous,
and so its crouching a source of danger. I have been particularly struck
with the fact that black rabbits inherit the crouching instinct as
strongly as do normally coloured ones, with the effect of rendering
themselves highly conspicuous. This shows that the instinct is not
necessarily correlated with the colour which alone renders the instinct
useful, but that both have developed simultaneously and independently,
and by natural selection. The fact also shows that the crouching of
rabbits is purely instinctive, and not due to any conscious process of
comparing their own colour with that of the surfaces on which they
crouch. No doubt the instinct began and was developed by natural
selection placing a premium upon the better judgment of those
individuals which know when best to seek safety in flight and when by
crouching--protective colouring being added at the same time by the same
agency.
Another fact, which every one who shoots must have observed, goes to
show the stupidity of rabbits, or their inability to learn by
experience. When alarmed they run for their burrows, and when they reach
them, instead of entering they very frequently squat down to watch the
enemy. Now, although they well know the distance at which it is safe to
allow a man with a gun to approach, excess of curiosity, or a mistaken
feeling of security in being so near their homes, induces the animals to
allow a man to approach within easy shooting distance. Yet that in
other respects rabbits can learn much by experience must be evident to
all who are accustomed to shoot with ferrets. From burrows which have
not been much ferreted, rabbits will bolt soon after the ferret is put
in; but this is not the case where rabbits have had previous experience
of the association between ferrets and sportsmen. Rather than bolt under
such circumstances, and so face the known danger of the waiting gun,
rabbits will often allow themselves to be torn with the ferrets' claws
and mutilated by their teeth. This is the case, no matter how silently
the sportsmen may conduct their operations; the mere fact of a ferret
entering their burrows seems to be enough to assure the rabbits that
sportsmen are waiting outside.[209]
In its emotions the rabbit is for the most part a very timid animal,
although the males fight severely with one another--having more strongly
developed than any other animal the strange but effectual instinct of
castrating their rivals. Moreover, even against other animals, rabbits
will, when compelled to do so, stand upon the defensive. To show this I
may quote a letter which several years ago I published in 'Nature:'--
I have occasion just now to keep over thirty Himalayan
rabbits in an outhouse. A short time ago it was
observed that some of these rabbits had been attacked
and slightly bitten by rats. Next day the person who
feeds the rabbits observed, upon entering the
outhouse, that nearly all the inmates were congregated
in one corner; and upon going to ascertain the cause,
found one rat dead, and another so much injured that
it could scarcely run. Both rats were of an unusually
large size, and their bodies were much mangled by the
rabbits' teeth.
I never before knew that domestic rabbits would fight
with any carnivorous antagonist. That wild rabbits
never do so I infer from having several times seen
ferrets turn out from the most crowded burrow in a
warren young stoats and weasels not more than four
inches long.
It is evident that the show-fight instinct cannot have
been developed in Himalayan rabbits by means of
natural selection, but it is no less evident that if
it ever arose in wild rabbits it would be preserved
and intensified by such means.
The following observation of my own on a previously unnoticed instinct
displayed by wild rabbits is, I think, of sufficient interest to render.
Most people are aware that if a rabbit is shot near the mouth of its
burrow, the animal will employ the last remnant of its life in
struggling into it. Having several times observed that wounded rabbits
which had thus escaped appeared again several days afterwards above
ground, lying dead a few feet from the mouth of the burrow, I wished to
ascertain whether the wounded animals had themselves come out before
dying, possibly for air, or had been taken out by their companions. I
therefore shot numerous rabbits while they were sitting near their
burrows, taking care that the distance between the gun and the animal
should be such as to insure a speedy, though not an immediate death.
Having marked the burrows at which I shot rabbits in this manner I
returned to them at intervals for a fortnight or more, and found that
about one-half of the bodies appeared again on the surface in the way
described. That this reappearance above ground is not due to the
victim's own exertions, I am now quite satisfied; for not only did two
or three days generally elapse before the body thus showed itself--a
period much too long for a severely wounded rabbit to survive--but in a
number of cases decomposition had set in. Indeed, on one occasion
scarcely anything of the animal was left save the skin and bones. This
was in a large warren.
It is a curious thing that I have hitherto been unable to get any bodies
returned to the surface, of rabbits which I _inserted_ into their
burrows _after death_. I account for this by supposing that the stench
of the decomposing carcass is not so intolerable to the other occupants
of the burrow when it is near the orifice as it is when further in.
Similarly, I find that there is not so good a chance of bodies being
returned from an extensive warren of intercommunicating holes, as there
is from smaller warrens or blind holes; the reason probably being that
in the one case the living inhabitants are free to vacate the offensive
locality, while in the other case they are not so. Anyhow, there can be
no reasonable doubt that the instinct of removing their dead has arisen
in rabbits from the necessity of keeping their confined domiciles in a
pure state.
_Hare._
The hare is a more intelligent animal than the rabbit. Possibly its much
greater powers of locomotion may be one cause of its mental superiority
to its nearest congener. I have never myself observed a hare commit the
mistake already mentioned in the case of the rabbit, viz., that of
crouching for concealment upon an inappropriately coloured surface. But
the best idea of the comparatively high intelligence of the hare will be
gained by the following quotations. The first of these is taken from
Loudoun's 'Magazine of Natural History' (vol. iv., p. 143):--
It is especially conscious of the scent left by its
feet, and of the danger which threatens it in
consequence; a reflection which implies as much
knowledge of the habits of its enemies as of its own.
When about to enter its seat for the purpose of rest,
it leaps in various directions, and crosses and
recrosses its path with repeated springs; and at last,
by a leap of greater energy than it has yet used, it
effects a lodgment in the selected spot, which is
chosen rather to disarm suspicion than to protect it
from injury. In the 'Manuel du Chasseur' some
instances are quoted from an ancient volume on hunting
by Jaques du Fouillouse. A hare intending to mislead
its pursuers has been seen spontaneously to quit its
seat and to proceed to a pond at the distance of
nearly a mile, and having washed itself, push off
again through a quantity of rushes. It has, too, been
known, when pursued to fatigue by dogs, to thrust
another hare from its seat and squat itself down in
its place. This author has seen hares swim
successively through two or three ponds, of which the
smallest was eighty paces round. He has known it,
after a long chase, to creep under the door of a
sheep-house and rest among the cattle, and when the
hounds were in pursuit, it would get into the middle
of a flock of sheep and accompany them in all their
motions round the field, refusing by any means to quit
the shelter they afforded. The stratagem of its
passing forward on one side of a hedge and returning
by the other, with only the breadth of the hedge
between itself and its enemies, is of frequent
occurrence, and it has even been known to select its
seat close to the walls of a dog-kennel. This latter
circumstance, however, is illustrative of the
principles of reflection and reasoning; for the fox,
weasel, and polecat are to the hare more dangerous
enemies than the hound; and the situations chosen were
such as those ferocious creatures were not likely to
approach. A gentleman was engaged in the amusement of
coursing, when a hare, closely pressed, passed under a
gate, while the dogs followed by leaping over it. The
delay caused to her pursuers by this manoeuvre seems
to have taught a sudden and useful lesson to the
persecuted creature; for as soon as the dogs had
cleared the gate and overtaken her, she doubled and
returned under the gate as before, the dogs again
following and passing over it. And this flirtation
continued backwards and forwards until the dogs were
fairly tired of the amusement; when the hare, taking
advantage of their fatigue, quietly stole away.
The following note, by Mr. Yarrell, is significant of a process of
reasoning derived from observations of the course of nature, such as
would do no discredit to a higher race of creatures:--
A harbour of great extent on our northern coast has an
island near the middle of considerable size, the
nearest point of which is a mile distant from the
mainland at high water, and with which point there is
frequent communication by a ferry. Early one morning
in spring two hares were observed to come down from
the hills of the mainland towards the sea-side; one of
which from time to time left its companion, and
proceeding to the very edge of the water, stopped
there a minute or two, and then returned to its mate.
The tide was rising, and after waiting some time, one
of them, exactly at high water, took to the sea, and
swam rapidly over, in a straight line, to the opposite
projecting point of land. The observer on this
occasion, who was near the spot, but remained
unperceived by the hares, had no doubt they were of
different sexes, and that it was the male (like
another Leander) which swam across the water, as he
had probably done many times before. It was remarkable
that the hares had remained on the shore nearly half
an hour; one of them occasionally examining, as it
would seem, the state of the current, and ultimately
taking to the sea at that precise period of the tide
called slackwater, when the passage across could be
effected without being carried by the force of the
stream either above or below the desired point of
landing. The other hare then cantered back to the
hills. (Loudoun's 'Magazine of Natural History,' vol.
v., p. 99.)
According to Couch ('Illustrations of Instinct,' p. 177)--
When followed by dogs, it will not run through a gate,
though this is obviously the most ready passage; nor
in crossing a hedge will it prefer a smooth and even
part, but the roughest, where thorns and briars
abound; and when it mounts an eminence it proceeds
obliquely, and not straightforward. And whether we
suppose these actions to proceed from a desire to
avoid those places where traps may probably have been
laid, or from knowing that his pursuers will exactly
follow his footsteps, and he has resolved to lead them
through as many obstacles as possible, in either case
an estimation of causes and consequences is to be
discovered.
It is a remarkable thing that both hares and rabbits should allow
themselves to be overtaken in the open field by weasels. I have myself
witnessed the process, and am at a loss to account for it. The hare or
rabbit seems perfectly aware of the dangerous character of the weasel,
and yet does not put forth its powers of escape. It merely toddles along
with the weasel toddling behind, until tamely allowing itself to be
overtaken. This anomalous case may perhaps be akin to the alleged
phenomena of the fascination of birds and small rodents by snakes; but
in any case there seems to have been here a remarkable failure of
natural selection in doing duty to the instincts of these swift-footed
animals.
We must not close this account of the intelligence of the hare genus
without alluding to the classical case of Cowper's hares. The following
abstract is taken from Tegg's edition of 'The Life and Works of William
Cowper,' p. 633:--
Puss was ill three days, during which time I nursed
him, kept him apart from his fellows, . . . and by
constant care, &c., restored him to perfect health. No
creature could be more grateful than my patient after
his recovery, a sentiment which he most significantly
expressed by licking my hand, first the back of it,
then the palm, then every finger separately, then
between all the fingers, as if anxious to leave no
part of it unsaluted; _a ceremony which he never
performed but once again upon a similar occasion_.
Finding him extremely tractable, I made it my custom
to carry him always after breakfast into the garden. . . .
I had not long habituated him to this taste of
liberty before he began to be impatient for the return
of the time when he might enjoy it. He would invite me
to the garden by drumming upon my knee, and by a look
of such expression as it was not possible to
misinterpret. If this rhetoric did not immediately
succeed, _he would take the skirt of my coat between
his teeth and pull it with all his force_. He seemed to
be happier in human society than when shut up with his
natural companions.
_Rats and Mice._
Rats are well known to be highly intelligent animals. Unlike the hare or
rabbit, their shyness seems to proceed from a wise caution rather than
from timidity; for, when circumstances require, their boldness and
courage in combat is surprising. Moreover, they never seem to lose their
presence of mind; for, however great their danger, they seem always
ready to take advantage of any favouring circumstances that may arise.
Thus, when matched with so formidable an opponent as a ferret in a
closed room, they have been known to display wonderful cunning in taking
advantage of the light--keeping close under the window so as to throw
the glare into the eyes of the enemy, darting forwards time after time
to deliver a bite, and then as often retiring to their vantage-ground.[210]
But the emotions of rats do not appear to be of an entirely selfish
character. There are so many accounts in the anecdote books of blind
rats being led about by their seeing companions, that it is difficult to
discredit an observation so frequently confirmed.[211] Moreover, rats
have been frequently known to assist one another in defending themselves
from dangerous enemies. Several observations of this kind are recorded
by the trustworthy writer Mr. Rodwell, in his somewhat elaborate work
upon this animal.
Again, as showing affection for human beings, I may quote the
following:--'The mouse which had been tamed by Baron Trench in his
prison having been taken from him, watched at the door and crept in when
it was opened; being removed again, it refused all food, and died in
three days.'[212]
With regard to general intelligence, every one knows the extraordinary
wariness of rats in relation to traps, which is only equalled in the
animal kingdom by that of the fox and the wolverine. It has frequently
been regarded as a wonderful display of intelligence on the part of rats
that while gnawing through the woodwork of a ship, they always stop
before they completely perforate the side; but, as Mr. Jesse suggests,
this is probably due to their distaste of the salt water. No such
disparaging explanation, however, is possible in some other instances of
the display of rat-intelligence. Thus, the manner in which they
transport eggs to their burrows has been too frequently observed to
admit of doubt. Rodwell gives a case in which a number of eggs were
carried from the top of a house to the bottom by two rats devoting
themselves to each egg, and alternately passing it down to each other at
every step of the staircase.[213] Dr. Carpenter also received from an
eye-witness a similar account of another instance.[214] According to the
article in the _Quarterly Review_, already mentioned, rats will not only
convey eggs from the top of the house to the bottom, but from bottom to
top. 'The male rat places himself on his fore-paws, with his head
downwards, and raising up his hind legs and catching the egg between
them, pushes it up to the female, who stands on the step above, and
secures it with her fore-paws till he jumps up to her; and this process
is repeated from step to step till the top is reached.'
'The captain of a merchantman,' says Mr. Jesse, 'trading to the port of
Boston, in Lincolnshire, had constantly missed eggs from his sea stock.
He suspected that he was robbed by his crew, but not being able to
discover the thief, he was determined to watch his store-room.
Accordingly, having laid in a fresh stock of eggs, he seated himself at
night in a situation that commanded a view of his eggs. To his great
astonishment he saw a number of rats approach; they formed a line from
his egg baskets to their hole, and handed the eggs from one to another
in their fore-paws.'[215]
Another device to which rats resort for the procuring of food is
mentioned in all the anecdote books, and it seemed so interesting that I
tried some direct experiments upon the subject. I shall first state the
alleged facts in the words of Watson:--
As to oil, rats have been known to get oil out of a
narrow-necked bottle in the following way:--One of
them would place himself, on some convenient support,
by the side of the bottle, and then, dipping his tail
into the oil, would give it to another to lick. In
this act there is something more than what we call
instinct; there is reason and understanding.[216]
Jesse also gives the following account:--
A box containing some bottles of Florence oil was
placed in a store-room which was seldom opened; the
box had no lid to it. On going to the room one day for
one of the bottles, the owner found that the pieces of
bladder and cotton at the mouth of each bottle had
disappeared, and that much of the contents of the
bottles had been consumed. The circumstance having
excited suspicion, a few bottles were refilled with
oil, and the mouths of them secured as before. Next
morning the coverings of the bottles had been removed,
and some of the oil was gone. However, upon watching
the room, which was done through a little window, some
rats were seen to get into the box, and insert their
tails into the necks of the bottles, and then
withdrawing them, they licked off the oil which
adhered to them.[217]
Lastly, Rodwell gives another case similar in all essential respects,
save that the rat licked its own tail instead of presenting it to a
companion.
The experiment whereby I tested the truth of these statements was a
very simple one. I recorded it in 'Nature' as follows:--
It is, I believe, pretty generally supposed that rats
and mice use their tails for feeding purposes when the
food to be eaten is contained in vessels too narrow to
admit the entire body of the animal. I am not aware,
however, that the truth of this supposition has ever
been actually tested by any trustworthy person, and so
think the following simple experiments are worth
publishing. Having obtained a couple of tall-shaped
preserve bottles with rather short and narrow necks, I
filled them to within three inches of the top with red
currant jelly which had only half stiffened. I covered
the bottles with bladder in the ordinary way, and then
stood them in a place infested by rats. Next morning
the bladder covering each of the bottles had a small
hole gnawed through it, and the level of the jelly was
reduced in both bottles to the same extent. Now, as
this extent corresponded to about the length of a
rat's tail if inserted at the hole in the bladder, and
as this hole was not much more than just large enough
to admit the root of this organ, I do not see that any
further evidence is required to prove the manner in
which the rats obtained the jelly, viz., by repeatedly
introducing their tails into the viscid matter, and as
repeatedly licking them clean. However, to put the
question beyond doubt, I refilled the bottles to the
extent of half an inch above the jelly level left by
the rats, and having placed a circle of moist paper
upon each of the jelly surfaces, covered the bottles
with bladder as before. I now left the bottles in a
place where there were no rats or mice, until a good
crop of mould had grown upon one of the moistened
pieces of paper. The bottle containing this crop of
mould I then transferred to the place where the rats
were numerous. Next morning the bladder had again been
eaten through at one edge, and upon the mould there
were numerous and distinct tracings of the rats'
tails, resembling marks made with the top of a
pen-holder. These tracings were evidently caused by
the animals sweeping their tails about in a fruitless
endeavour to find a hole in the circle of paper which
covered the jelly.
With regard to mice, the Rev. W. North, rector of Ashdown, in Essex,
placed a pot of honey in a closet, in which a quantity of plaster
rubbish had been left by builders. The mice piled up the plaster in the
form of a heap against the sides of the pot, in order to constitute an
inclined plane whereby to reach the rim. A quantity of the rubbish had
also been thrown into the pot, with the effect of raising the level of
the honey that remained to near the rim of the pot; but, of course, the
latter fact may have been due to accident, and not to design.[218] This is
a case in which mal-observation does not seem to have been likely.
Powelsen, a writer on Iceland, has related an account of the
intelligence displayed by the mice of that country, which has given rise
to a difference of competent opinion, and which perhaps can hardly yet
be said to have been definitely settled. What Powelsen said is that the
mice collect in parties of from six to ten, select a flat piece of dried
cow-dung, pile berries or other food upon it, then with united strength
drag it to the edge of any stream they wish to cross, launch it, embark,
and range themselves round the central heap of provisions with their
heads joined over it, and their tails hanging in the water, perhaps
serving as rudders. Pennant afterwards gave credit to this account,
observing that in a country where berries were scarce, the mice were
compelled to cross streams for distant forages.[219] Dr. Hooker, however,
in his 'Tour in Iceland,' concludes that the account is a pure
fabrication. Dr. Henderson, therefore, determined on trying to arrive at
the truth of the matter, with the following result:--'I made a point of
inquiring of different individuals as to the reality of the account, and
am happy in being able to say that it is now established as an important
fact in natural history by the testimony of two eye-witnesses of
unquestionable veracity, the clergyman of Briamslaek, and Madame
Benedictson of Stickesholm, both of whom assured me that they had seen
the expedition performed repeatedly. Madame Benedictson, in particular,
recollected having spent a whole afternoon, in her younger days, at the
margin of a small lake on which these skilful navigators had embarked,
and amusing herself and her companions by driving them away from the
sides of the lake as they approached them. I was also informed that
they make use of dried mushrooms as sacks, in which they convey their
provisions to the river, and thence to their homes.'[220]
Before leaving the mice and rats I may say a few words upon certain
mouse- and rat-like animals which scarcely require a separate section
for their consideration. Of the harvesting mouse Gilbert White says:--
One of their nests I procured this autumn, most
artificially plaited and composed of blades of wheat,
perfectly round, and about the size of a cricket-ball,
with the aperture so ingeniously closed that there was
no discovering to what part it belonged. It was so
compact and well filled that it would roll across the
table without being discomposed, though it contained
eight little mice that were naked and blind. As the
nest was perfectly full, how could the dam come at her
litter respectively, so as to administer a teat to
each? Perhaps she opens different places for that
purpose, adjusting them again when the business is
over; but she could not possibly be contained herself
in the ball with the young ones, which, moreover,
would be daily increasing in size. This wonderful
procreant cradle, an elegant instance of the efforts
of instinct, was found in a wheat field, suspended on
the head of a thistle.
Pallas has described the provident habits of the so-called 'rat-hare'
(_Lagomys_), which lays up a store of grass, or rather hay, for winter
consumption. These animals, which occur in the Altai Mountains, live in
holes or crevices of rock. About the middle of the month of August they
collect grass, and spread it out to dry into hay. In September they form
heaps or stacks of the hay, which may be as much as six feet high, and
eight feet in diameter. It is stored in their chosen hole or crevice,
protected from the rain.
The following is quoted from Thompson's 'Passions of Animals,' pp.
235-6:--
The life of the harvester rat is divided between
eating and fighting. It seems to have no other passion
than that of rage, which induces it to attack every
animal that comes in its way, without in the least
attending to the superior strength of its enemy.
Ignorant of the art of saving itself by flight,
rather than yield, it will allow itself to be beaten
to pieces with a stick. If it seizes a man's hand, it
must be killed before it will quit its hold. The
magnitude of the horse terrifies it as little as the
address of the dog, which last is fond of hunting it.
When a harvester perceives a dog at a distance, it
begins by emptying its cheek-pouches, if they happen
to be filled with grain; it then blows them up so
prodigiously, that the size of the head and neck
greatly exceeds that of the rest of the body. It rears
itself upon its hind legs, and thus darts upon the
enemy. If it catches hold, it never quits it but with
the loss of its life; but the dog generally seizes it
behind, and strangles it. This ferocious disposition
prevents it from being at peace with any animal
whatever. It even makes war against its own species.
When two harvesters meet, they never fail to attack
each other, and the stronger always devours the
weaker. A combat between a male and a female commonly
lasts longer than between two males. They begin by
pursuing and biting each other, then each of them
retires aside, as if to take breath. After a short
interval they renew the combat, and continue to fight
till one of them falls. The vanquished uniformly
serves as a repast to the conqueror.
If we contrast the fearless disposition of the harvester with the
timidity of the hare or rabbit, we observe that in respect of emotions,
no less than in that of intelligence, the order Rodentia comprises the
utmost extremes.
The so-called 'prairie-dog' is a kind of small rodent, which makes
burrows in the ground, and a slight elevation above it. The animals
being social in their habits, their warrens are called 'dog-towns.'
Prof. Jillson, Ph.D., kept a pair in confinement (see 'American
Naturalist,' vol. v., pp. 24-29), and found them to be intelligent and
highly affectionate animals. These burrows he found to contain a
'granary,' or chambers set apart for the reception of stored food. With
regard to the association said to exist between this animal and the owl
and rattle-snake, Prof. Jillson says, 'I have seen many dog-towns, with
owls and dogs standing on contiguous, and in some cases on the same
mound, but never saw a snake in the vicinity.' The popular notion that
the owl acts the part of sentry to the dog requires, to say the least,
confirmation.
_Beaver._
Most remarkable among rodents for instinct and intelligence
unquestionably stands the beaver. Indeed, there is no animal--not even
excepting the ants and bees--where instinct has risen to a higher level
of far-reaching adaptation to certain constant conditions of
environment, or where faculties, undoubtedly instinctive, are more
puzzlingly wrought up with faculties no less undoubtedly intelligent. So
much is this the case that, as we shall presently see, it is really
impossible by the closest study of the psychology of this animal to
distinguish the web of instinct from the woof of intelligence; the two
principles seem here to have been so intimately woven together, that in
the result, as expressed by certain particular actions, it cannot be
determined how much we are to attribute to mechanical impulse, and how
much to reasoned purpose.
Fortunately, the doubt that for many years shrouded the facts has been
dispelled by the conscientious and laborious observations of the late
Mr. Lewis H. Morgan,[221] whose work throughout displays the judicious
accuracy of a scientific mind. As this is much the most trustworthy, as
well as the most exhaustive essay upon the subject, I shall mainly rely
upon it for my statement of facts, and while presenting these I shall
endeavour to point out the psychological explanation, or difficulty of
explanation, to which they are severally open.
The beaver is a social animal, the male living with his single female
and progeny in a separate burrow or 'lodge.' Several of these lodges,
however, are usually built close together, so as to form a beaver
colony. The young quit the lodge of their parents when they enter upon
the summer of their third year, seek mates, and establish new lodges for
themselves. As each litter numbers three or four, and breeding is
annual, it follows that a beaver lodge never or rarely contains more
than twelve individuals, while the number usually ranges from four to
eight. Every season, and particularly when a district becomes
overstocked, some of the beavers migrate. The Indians say that in their
local migrations the old beavers go up stream, and the young down;
assigning as a reason that in the struggle for existence greater
advantages are afforded near the source than lower down a stream, and
therefore that the old beavers appropriate the former. But although
lodges may thus be vacated by the old beavers, they are not left
tenantless; their lease is, as it were, transferred to another beaver
couple. This process of transference of ownership goes on from
generation to generation, so that the same lodges are continuously
occupied for centuries.
These lodges, which are always constructed in or near water, are of
three kinds--the island, bank, and lake lodge. The first are formed on
small islands which may happen to occur in the ponds made by the
beaver-dams. The floor of the lodge is a few inches above the level of
the water, and into it there open two, or sometimes more entrances:
These are made with great skill, and in the most
artistic manner. One is straight, or as nearly so as
possible, with its floor, which is of course under
water, an inclined plane, rising gradually from the
bottom of the pond into the chamber; while the other
is abrupt in its descent, and often sinuous in its
course. The first we shall call the 'wood entrance,'
from its evident design to facilitate the admission
into the chamber of their wood cuttings, upon which
they subsist during the season of winter. These
cuttings, as will elsewhere be shown, are of such size
and length that such an entrance is absolutely
necessary for their free admission into the lodge. The
other, which we shall call the 'beaver entrance,' is
the ordinary run-way for their exit and return. It is
usually abrupt, and often winding. In the lodge under
consideration, the wood entrance descended from the
outer run of the chamber entrance about ten feet to
the bottom of the pond in a straight line, and upon an
inclined plane; while the other, emerging from the
line of the chamber at the side, descended quite
abruptly to the bottom of the moat or trench, through
which the beavers must pass, in open water, out into
the pond. Both entrances were rudely arched, with a
roof of interlaced sticks filled in with mud
intermixed with vegetable fibre, and were extended to
the bottom of the pond or trench, with the exception
of the opening at their ends. At the places where they
were constructed through the floor they were finished
with neatness and precision; the upper parts and sides
forming an arch more or less regular, while the bottom
and floor edges were formed with firm and compacted
earth, in which small sticks were embedded. It is
difficult to realise the artistic appearance of some
of these entrances without actual inspection.
Upon the floor of the lodge there is constructed a house of sticks,
brushwood, and mud, in the form of a circular or oval chamber, the size
of which varies with the age of the lodge; for by a continuous process
of repair (which consists in removing the decayed sticks, &c., from the
interior and working them up with new material upon the exterior) the
whole lodge progressively increases in size: eventually in this way the
interior chamber may attain a diameter of seven or eight feet.
The 'bank lodges' are of two kinds:--
One is situated upon the bank of the stream or pond, a
few feet back from its edge, and entered by an
underground passage from the bed of the stream,
excavated through the natural earth up into the
chamber. The other is situated upon the edge of the
bank, a portion of it projecting over and resting upon
the bed of the channel, so as to have the floor of the
chamber rest upon the bank as upon solid ground, while
the external wall on the pond side projects beyond it,
and is built up from the bottom of the pond.
Lastly, the 'lake lodges' are constructed on the shores of lakes, which,
being usually shelving and hard, require some further variation in the
structure of the lodges. These, therefore, are of interest 'as
illustrations of the capacity of the beavers to vary the mode of
construction of their lodges in accordance with the changes of
situation.' One-half or two-thirds of the lodge is in this case 'built
out upon the lake for the obvious purpose of covering the entrance, as
well as for its extension into deep water.'
All these forms of lodge are, historically regarded, modified burrows.
The beaver is a burrowing animal. Indulging this
propensity, he excavates chambers underground, and
constructs artificial lodges upon its surface, both of
which are indispensable to his security and happiness.
The lodge is but a burrow above ground, covered with
an artificial roof, and possesses some advantages over
the latter as a place for rearing young.
There are reasons for believing that the burrow is the
normal residence of the beavers, and that the lodge
grew out of it, in the progress of their experience,
by a process of natural suggestion. . . . In addition
to the lodge, the same beavers who inhabit it have
burrows in the banks surrounding the pond. They never
risk their personal safety upon their lodge alone,
which, being conspicuous to their enemies, is liable
to attack. . . . As the entrances are always below the
surface level of the pond, there are no external
indications to mark the site of the burrow,
except occasionally a small pile of beaver-cuttings a foot or more high.
These, the trappers affirm, are purposely left there by the beavers to
keep the snow loose over the ends of their burrows during winter for the
admission of air.
Mr. Morgan adds the very probable suggestion that this habit of piling
up cuttings for purposes of ventilation may have constituted the origin
of lodge-building.
It is but a step from such a surface-pile of sticks to
a lodge, with its chamber above ground, and the
previous burrow as its entrance from the pond. A
burrow accidentally broken through at its upper end,
and repaired with a covering of sticks and earth,
would lead to a lodge above ground, and thus
inaugurate a beaver lodge out of a broken burrow.
It is evidence of an important local variation of instinct, that in the
Cascade Mountains the beavers live chiefly in burrows in the banks of
streams, and rarely construct either lodges or dams. Dr. Newbury, in his
report on the zoology of Oregon and California, says: 'We found the
beavers in numbers, of which, when applied to beavers, I had no
conception,' and yet 'we never saw their houses and seldom a dam.'
Whether this local variation be due to a relapse from dam- and
lodge-building instincts to the primitive burrowing instinct, or to a
failure in the full development of the newer instinct, is immaterial.
Probably, I think, looking to the high antiquity of the building
instinct, and also to its being occasionally manifested by the
Californian beavers, their case is to be regarded as one of relapsing
instinct.
In selecting the site of their lodges beavers display much sagacity and
forethought.
The severity of the climate in these high northern
latitudes lays upon them the necessity of so locating
their lodges as to be assured of water deep enough in
their entrances, and also so protected in other
respects, as not to freeze to the bottom;[222] otherwise
they would perish with hunger, locked up in ice-bound
habitations. To guard against this danger, the dam,
also, must be sufficiently stable through the winter
to maintain the water at a constant level; and this
level, again, must be so adjusted with reference to
the floor of the lodge as to enable them, at all
times, to take in their cuttings from without as they
are needed for food. When they leave their normal mode
of life in the banks of the rivers, and undertake to
live in dependence upon artificial ponds of their own
formation, they are compelled to prevent the
consequences of their acts at the peril of their
lives.
On the upper Missouri, where the banks of the river are for miles
together vertical, and rising from three to eight feet above its
surface, the beavers resort to the device of making what are called
'beaver slides.' These are narrow inclined planes cut into the banks at
intervals, the angle of inclination being 45° to 60°, so as to form a
gradual descent from a point a few feet back from the edge of the bank
to the level of the river. As Mr. Morgan observes, 'they furnish another
conspicuous illustration of the fact that beavers possess a free
intelligence, by means of which they are enabled to adapt themselves to
the circumstances in which they are placed.'
Coming now to the habits of these animals in connection with the
procuring and storing of food, it is first to be observed that 'the
thick bark upon the trunks of large trees, and even upon those of medium
size, is unsuitable for food; but the smaller limbs, the bark of which
is tender and nutritious, afford the aliment which they prefer.' To
obtain this food, the animals, as is well known, fell the trees by
gnawing a ring round their base. Two or three nights' successive work by
a pair of beavers is enough to bring down a half-grown tree, 'each
family being left to the undisturbed enjoyment of the fruits of their
own toil and industry.' '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 cracking noise of the
tree-fall might attract some enemy to the place.' It is of much interest
that the beavers when thus felling trees know how to regulate the
direction of the fall; by gnawing chiefly on the side of the trunk
remote from the water, they make the tree fall towards the water, with
the obvious purpose of saving as much as possible the labour of
subsequent transport. For as soon as a tree is down, the next work is to
cut off the branches, or such as are from two to six inches in diameter;
and then, when they have been cleared of their twigs, to divide them
into lengths sufficient to admit of the beavers transporting them to
their lodges. The cutting into lengths is effected by making a number of
semi-sections through the branch at more or less equal distances as it
lies upon the ground, and then turning the branch half round and
continuing the sections from the opposite side. 'To cut it (the branch)
entirely through from the upper side would require an incision of such
width as to involve a loss of labour.' The thicker the branch, the
closer together are the sections made, and consequently the shorter are
the resulting portions--the reason, of course, being that the strength
of the animal would not be sufficient to transport a thick piece of
timber of the same length as a thin piece which it is only just able to
manage.
In moving cuttings of this description they are quite
ingenious. They shove and roll them with their hips,
using also their legs and tails as levers, moving
sideways in the act. In this way they move the larger
pieces from the more or less elevated ground on which
the deciduous trees are found, over the uneven but
generally descending surface to the pond. . . . After
one of these cuttings has been transported to the water,
a beaver, placing one end of it under his throat, pushes
it before him to the place where it is to be sunk.
The sinking is no doubt partly effected by mere soaking; but there is
also some evidence to show that the beavers have a method of anchoring
down their supplies. Thus they have been observed towing pieces of brush
to their lodges, and then, while holding the large end in their mouths,
'going down with it to the bottom, apparently to fix it in the mud
bottom of the pond.' A brush-heap being thus formed, the cuttings from
the felled trees are stuck through the brushwork, without which
'protection they would be liable to be floated off by the strong
currents, and thus be lost to the beavers at the time when their lives
might depend upon their safe custody.'
Lastly, as a method whereby the beavers can save themselves the trouble
of cutting, transporting, and anchoring all at the same time, they are
prone, when circumstances permit, to fell a tree growing near enough to
their pond to admit of its branches being submerged in the water. The
animals then well know that the branches and young shoots will remain
preserved throughout the winter without any further trouble from them.
But of course the supply of trees thus growing conveniently near a
beaver-pond is too limited to last long.
We have next to consider the most wonderful, and I think the most
psychologically puzzling structures that are presented as the works of
any animal; I mean, of course, the dams and canals.
The object of the dam is that of forming an artificial pond, the use of
which is to afford refuge to the animals as well as water connection
with their lodges. Therefore the level of the pond must in all cases be
higher than that of the lodge- and burrow-entrances, and it is usually
maintained two or three feet above them.
As the dam is not an absolute necessity to the beaver
for the maintenance of his life--his normal habitation
being rather natural ponds and rivers, and the burrows
in their banks--it is, in itself considered, a
remarkable fact that he should have voluntarily
transferred himself, by means of dams and ponds of his
own construction, from a natural to an artificial mode
of life.
In external appearance there are two distinct kinds of dams, although
all are constructed on the same principle. One, the more common, is the
'stick dam,' which is composed of interlaced stick and pole work upon
the lower face, with an embankment of earth mixed with the same
materials on the upper face. The other is the 'solid-bank dam,' which
differs from the former in having much more brush and mud worked into
its construction, especially upon its surfaces; the result being that
the whole formation looks like a solid bank of earth. In the first kind
of dam the surplus water percolates through the structure along its
entire length; but in the second kind the discharge takes place through
a single furrow in the crest, which, remarkable though the fact
unquestionably is, the beavers intentionally form for this purpose.
In the construction of the dam, stones are used here and there to give
down-weight and solidity. These stones weigh from one to six pounds, and
are carried by the beavers in the same way as they carry their
mud--namely, by walking on their hind legs while holding their burden
against the chest with their fore-paws. The solid dams are much firmer
in their consistence than the stick dams; for while a horse might walk
across the former, the weight of a man would be too great to be
sustained by the latter. Each kind of dam is adapted to the locality in
which it is built, the difference between the two kinds being due to the
following cause. As a stream gains water and force in its descent, it
develops banks, and also a broader and deeper channel. These banks
assume a vertical form in the level areas where the soil is alluvial.
Thus, an open stick-work dam could not in such places be led off from
either bank; and even if it could, the force and depth of the stream
would carry it away. Therefore in such places the beavers build their
solid-bank dams, while in shallow and comparatively sluggish waters they
content themselves with the smaller amount of labour involved in the
building of a stick dam.
To give some idea of the proportions of a dam, I shall epitomise a
number of measurements given by Mr. Morgan:--
Feet
Height of structure from base line 2 to 6
Difference in depth of water above and below dam 4 to 5
Width of base or section 6 to 18
Length of slope, lower face 6 to 13
Length of slope, upper face 4 to 8
The only other measurement is that of length, and this, of course,
varies with the width of water to be spanned. Where this width is
considerable the length of a dam may be prodigious, as the following
quotation will show:--
Some of the dams in this region are not less
remarkable for their prodigious length, a statement of
which, in fact, would scarcely be credited unless
verified by actual measurement. The largest one yet
mentioned measures 260 feet, but there are dams 400
and even 500 feet long.
There is a dam in two sections, situated upon a
tributary of the main branch of the Esconauba River,
about a mile and a half north-west of the Washington
Main. One section measures 110 and the other 400 feet,
with an interval of natural bank, worked here and
there, of 1,000 feet. A solid-bank dam, 20 feet in
length, was first constructed across the channel of
the stream, from bank to bank, with the usual opening
for the surplus water, five feet wide. As the water
rose and overflowed the bank on the left side, the dam
was extended for 90 feet, until it reached ground high
enough to confine the pond. This natural bank extended
up the stream, and nearly parallel with it, for 1,000
feet, where the ground again subsided, and allowed the
water in the upper part of the pond to flow out and
around into the channel of the stream below the dam.
To meet this emergency a second dam, 420 feet long,
was constructed. For the greater part of its length it
is low, but in some places it is two and a half and
three feet high, and constructed of stick-work on the
land, and with an earth embankment on its outer face.
In effect, therefore, it is one structure 1,530 feet
in length, of which 530 feet in two sections is
artificial, and the remainder natural bank, but worked
here and there where depressions in the ground
required raising by artificial means.
It is truly an astonishing fact that animals should engage in such vast
architectural labours with what appears to be the deliberate purpose of
securing, by such very artificial means, the special benefits that arise
from their high engineering skill. So astonishing, indeed, does this
fact appear, that as sober-minded interpreters of fact we would fain
look for some explanation which would not necessitate the inference that
these actions are due to any intelligent appreciation, either of the
benefits that arise from the labour, or of the hydrostatic principles to
which this labour so clearly refers. Yet the more closely we look into
the subject, the more impossible do we find it to account for the facts
by any such easy method. Thus it seems perfectly certain that the
beavers, properly and strictly speaking, understand the use of their
dams in maintaining a certain level of water. For it is unquestionable
that in the solid-bank dams, as already observed, a regular opening or
trough is cut at one part of its crest to provide for the overflow; and
now it has to be added that this opening is purposely widened or
narrowed with reference to the amount of water in the stream at
different times, so as to ensure the maintenance of a constant level in
the pond. Similarly, though by different means, the same end is secured
in the case of the stick dams. For 'in most of these dams the rapidity
or slowness with which the surplus water is discharged is undoubtedly
regulated by the beavers; otherwise the level of the pond would
continually vary. There must be a constant tendency to enlarge the
orifices through which the water passes,' when the stream is small, and
_vice versâ_; otherwise the lodges would be either inundated or have
their sub-aquatic entrances exposed.[223] Moreover, a very little
consideration is enough to show that in stick dams the tendency to
increased leakage from the effects of percolation, and to a settling
down of the dam as its materials decay from underneath, must demand
unceasing vigilance and care to avert the consequences. And accordingly
it is found that 'in the fall of the year a new supply of materials is
placed upon the lower face of these dams to compensate this waste from
decay.'
Now, it is obvious that we have here presented a continual variation of
conditions, imposed by continual variations in the amount of water
coming down; and it is a matter of observation that these variations are
met by the beavers in the only way that they can be met--namely, by
regulating the amount of flow taking place through the dams. It will
therefore be seen that we have here to consider a totally different case
from that of the operation of pure instinct, however wonderful such
operation may be. For the adaptations of pure instinct only have
reference to conditions that are unchanging; so that if in this case we
suppose pure instinct to account for all the facts, we must greatly
modify our ideas of what pure instinct is taken to mean. Thus we must
suppose that when the beavers find the level of their ponds rising or
falling, the discomfort which they experience acts as a stimulus to
cause them, without intelligent purpose, either to widen or to narrow
the orifices in their dams as the case may be. And not only so, but the
conditions of stimulation and response must be so nicely balanced that
the animals widen or narrow these orifices with a more or less precise
_quantitative_ reference to the degree of discomfort, actual or
prospective, which they experience. Now it seems to me that even thus
far it is an extremely difficult thing to believe that the mechanism of
pure or wholly unintelligent instinct could admit of sufficient
refinement to meet so complex a case of compensating adaptation; and, as
we shall immediately see, this difficulty increases still more as we
contemplate additional facts relating to these structures.
Thus it sometimes happens that in large dams the pressure of the water
which they keep back is so considerable that their stability is
endangered. In such cases it has been observed by Mr. Morgan that, at a
short distance beneath the main dam, another and lower dam is thrown
across the stream, with the result of forming a shallow pond between the
two. This pond is--
Of no apparent use for beaver occupation, but yet
subserving the important purpose of setting back water
to the depth of twelve or fifteen inches; . . . and the
small dam, by maintaining the water a foot deep below
the great dam, diminishes to this extent the
difference in level above and below, and neutralises
to the same extent the pressure of the water in the
pond above against the main structure.
'Whether,' adds Mr. Morgan, with commendable caution, 'the lower dam was
constructed with this motive and for this object, or is explainable on
some other hypothesis, I shall not venture an opinion.' But as, he
further adds, 'I have also found the same precise work repeated below
other large dams,' we are led to conclude that their correlation cannot
at least be accidental; and as it is of so definite a character, there
really seems no 'other hypothesis' open to us than that of its having
reference to the stability of the main dam. Yet, if this is the case, it
becomes in my opinion simply impossible to attribute the fact to the
operation of pure instinct.
Again, Mr. Morgan observed one case in which, higher up stream than the
main dam, there was constructed another dam, ninety-three feet long, and
two and a half feet high at the centre:--
A dam at this point is apparently of no conceivable
use to improve the lake for beaver occupation. It has
one feature, also, in which it differs from other dams
except those upon lake outlets, and that consists in
its elevation, at all points, of about two feet above
the level of the lake at ordinary stages of the water.
In all other dams, except those upon lake outlets, and
in most of the latter, the water stands quite near
their crests, while in the one under consideration it
stood about two feet below it. This fact suggests at
least the inference, although it may have but little
of probability to sustain it, that it was constructed
with special reference to sudden rises of the lake in
times of freshet, and that it was designed to hold
this surplus water until it could be gradually
discharged through the dam into the great space below.
It would at least subserve this purpose very
efficiently, and thus protect the dam below it from
the effects of freshets. To ascribe the origin of this
dam to such motives of intelligence is to invest this
animal with a higher degree of sagacity than we have
probable reason to concede to him, and yet it is
proper to mention the relation in which these dams
stand to each other--whether that relation is regarded
as accidental or intentional.
As before, we have here to commend the caution displayed by the closing
sentence; but, as useless dams are not found in other places, the
inference clearly is that the dam in question, both as regards its
exceptional position and exceptional height, can only be explained by
supposing the structure to have been designed for the use which it
unquestionably served. That is to say, if we do not entertain this
explanation, there is no other to be suggested; and although in any
ordinary or occasional instance of the display of animal intelligence in
such a degree as this I should not hesitate to attribute the facts to
accident, in the case of the beaver there are such a multitude of
constantly recurring facts, all and only referable to a practical though
not less extraordinary appreciation of hydrostatic principles, that the
hypothesis of accident must here, I think, be laid aside. To
substantiate this statement I shall detail the facts concerning the
beaver-canals.
As Mr. Morgan, who first discovered and described these astonishing
structures, observes,--
Remarkable as the dam may still be considered, from
its structure and objects, it scarcely surpasses, if
it may be said to equal, these water-ways, here called
canals, which are excavated through the low lands
bordering their ponds for the purpose of reaching the
hard wood, and for affording a channel for its
transportation to their lodges. To conceive and
execute such a design presupposes a more complicated
and extended process of reasoning than that required
for the construction of a dam, and, although a much
simpler work to perform when the thought was fully
developed, it was far less to have been expected from
a mute animal.
These canals are developed in this way. One of the principal objects
served by a dam thrown across a small stream, is that of flooding the
low ground so as to obtain water connection with the first high ground
upon which hard wood is to be found, such connection being convenient,
or even necessary, for the purposes of transport.
Where the pond fails to accomplish this fully, and
also where the banks are defined and mark the limits
of the pond, the deficiency is supplied by the canals
in question. On descending surfaces, as has elsewhere
been stated, beavers roll and drag their short
cuttings down into the ponds. But where the ground is
low it is generally so uneven and rough as to render
it extremely difficult, if not impossible, for the
beavers to move them for any considerable distance by
physical force. Hence the canal for floating them
across the intervening level ground to the pond. The
necessity for it is so apparent as to diminish our
astonishment at its construction; and yet that the
beaver should devise a canal to surmount this
difficulty is not the less remarkable.
The canals, which are made by excavation, are usually from three to five
feet wide, three feet deep, and perhaps hundreds of feet long--the
length of course depending on the distance between the lodge and the
wood supply. They are cut in the form of trenches, having perpendicular
sides and abrupt ends. All roots of trees, under-brush, &c., are cleared
away in their course, so as to afford an unobstructed passage. These
canals are of such frequent occurrence that it is impossible to
attribute them to accident; they are evidently made, at the cost of much
labour, with the deliberate purpose of putting them to the use for which
they are designed. In executing this purpose there is sometimes
displayed a depth of engineering forethought over details of structure
required by the circumstances of special localities, which is even more
astonishing than the execution of the general idea. Thus it not
unfrequently happens that when a canal has been run for a certain
distance, a rise in the level of the ground renders it impossible to
continue the structure further from the water supply or lodge-pond,
without either incurring a great amount of labour in digging the canal
with progressively deepening sides, or leaving the trench empty of
water, and so useless. In such cases the beavers resort to various
expedients, according to the nature of the ground.
[Illustration]
Mr. Morgan gives an interesting sketch of one such case, where the canal
is excavated through low ground for a distance of 450 feet, when it
reaches the first rise of ground, and throughout this distance, being
level with the pond, it is supplied with water from this source. Where
the rise begins a dam is made, and the canal is then continued for 25
feet at a level of one foot higher than before. This higher level reach
is supplied with water collected from still higher levels by another
dam, extending for 75 feet upon one side of the canal and 25 feet on the
other, in the form of a crescent with its concavity directed towards the
highlands, so as to collect all the drainage water, and concentrate it
into the second reach of the canal. Beyond this larger dam there is
another abrupt rise of a foot, and the canal is there continued for 47
feet more, where a third dam is built resembling the second in
construction, only having a still wider span on either side of the canal
(142 feet), so as to catch a still larger quantity of drainage water to
supply the third or uppermost reach of the canal. We have, therefore,
here presented, not only a perfect application of the principle of
'locks,' which are used in canals of human construction, but also the
principle of collecting water to supply the reaches situated on the
slope by means of elaborately constructed dams of wide extent, and of
the best form for the purpose. There is thus shown much too great a
concurrence of engineering principles to the attainment of one object to
admit of our attributing the facts to accident. On this structure Mr.
Morgan observes:--
The crests of these dams where they cross the canals
are depressed, or worn down, in the centre, by the
constant passage of beavers over them while going to
and fro and dragging their cuttings. This canal with
its adjuncts of dams and its manifest objects is a
remarkable work, transcending very much the ordinary
estimates of the intelligence of the beaver. It served
to bring the occupants of the pond into easy
connection by water with the trees that supplied them
with food, as well as to relieve them from the tedious
and perhaps impossible task of transporting their
cuttings 500 feet over uneven ground unassisted by any
descent.
Again, in another case, also sketched by Mr. Morgan, another device is
resorted to, and one which, having reference to the particular
circumstances of the case, is the best that could have been adopted.
Here the canal, proceeding from the pond to the woodland 150 feet
distant, encounters at the woodland a rising slope covered with hard
wood. Thereupon the canal bifurcates, and the two diverging branches or
prongs are carried in opposite directions along the base of the woodland
rise, one for a distance of 100 and the other for 115 feet. The level
being throughout the same, the water from the pond supplies the two
branch-canals as well as the trunk. Both branches end with abrupt
vertical faces. Now the object of these branches is sufficiently
apparent:--
After the rising ground, and with it the hard wood
trees, were reached at the point where it branches,
there was no very urgent necessity for the branches.
But their construction along the base of the high
ground gave them a frontage upon the canal of 215 feet
of hard-wood lands, thus affording to them, along this
extended line, the great advantages of water
transportation for their cuttings.
One more proof of engineering purpose in the construction of canals will
be sufficient to place beyond all question the fact that beavers form
these canals, as they form their dams, with a far-seeing perception of
the suitability of highly artificial means to the attainment of
particular ends, under a variety of special circumstances. Mr. Morgan
observed one or two instances where the land included in a wind or loop
of a river was cut through by a beaver canal across the narrowest part,
'apparently to shorten the distance in going up and down by water.'
Judging from the figures which he gives, drawn to measurement, there can
be no question that such was the object; and as these structures may be
one or two hundred feet in length, and represent the laborious
excavation of some 1,500 cubic feet of soil, the animals must be
actuated by the most vivid conception of the subsequent saving in labour
that is to be effected by making an artificial communication across the
chord of an arc, instead of always going round the natural curve of a
stream.
Regarding now together all these facts relating to the psychology of the
beaver, it must be confessed, as I said at the outset, that we have
presented to us a problem perhaps the most difficult of any that we have
to encounter in the whole range of animal intelligence. On the one hand,
it seems incredible that the beaver should attain to such a level of
abstract thought as would be implied by his forming his various
structures with the calculated purpose of achieving the ends which they
undoubtedly subserve. On the other hand, as we have seen, it seems
little less than impossible that the formation of these structures can
be due to instinct. Yet one or other hypothesis, either singly or in
combination, must be resorted to. The case, it will be observed, thus
differs from that of the more wonderful performances of instinct
elsewhere, such as that of ants and bees, inasmuch as the performances
here are so complex and varied, as well as having reference to physical
principles of a much more recondite or less observable nature. The case
from its theoretical side being thus one of much difficulty, I think it
will be better to postpone its discussion till in 'Mental Evolution' I
come to treat of the whole subject of instinct in relation to
intelligence.
I must not, however, conclude this epitome of the facts without alluding
to the only other publication on the habits of the beaver which is of
distinctly scientific value. This is a short but interesting paper by
Prof. Alexander Agassiz.[224] He says that the largest dam he has himself
seen measured 650 feet in length, and 3-1/2 feet in height, with a small
number of lodges in the vicinity of the pond. The number of lodges is
always thus very small in proportion to the size of the dam, the
greatest number of lodges that he has observed upon one pond being five.
It is evident from this that beavers are not really gregarious in their
habits, and that their dams and canals 'are the work of a comparatively
small number of animals; but to make up for the numbers the work of
succeeding inhabitants of any one pond must have been carried on for
centuries to accomplish the gigantic results we find in some
localities.'
In one case Prof. Agassiz obtained what may be termed geological
evidence of the truth of an opinion advanced by Mr. Morgan, that
beaver-works may be hundreds if not thousands of years in course of
continuous formation. For the purpose of obtaining a secure foundation
for a mill dam erected above a beaver dam, it was necessary to clear
away the soil from the bottom of the beaver pond. This soil was found to
be a peat bog. A trench was dug into the peat 12 feet wide by 1,200 feet
long, and 9 feet deep; all the way along this trench old stumps of trees
were found at various depths, some still bearing marks of having been
gnawed by beavers' teeth. Agassiz calculated the growth of the bog as
about a foot per century, so that here we have tolerably accurate
evidence of an existing beaver dam being somewhere about a thousand
years old.
The gradual growth of these enormous dams has the effect of greatly
altering the configuration of the country where they occur. By taking
levels from dams towards the sources of streams on which they occur,
Agassiz was able ideally to reconstruct the original landscape before
the growth of the dams, and he found that, 'from the nature of the
surrounding country, the open spaces now joining the beaver ponds--the
beaver meadows where the trees are scanty or small--must at one time
have been all covered with forests.' At first the beavers 'began to
clear the forest just in the immediate vicinity of the dams, extending
in every direction, first up the stream as far as the nature of the
creek would allow, and then laterally by means of their canals, as far
as the level of the ground would allow, thus little by little clearing a
larger area according to the time they have occupied any particular
place,' In this way beavers may change the whole aspect of large tracts
of country, covering with water a great extent of ground which was once
thickly wooded.
FOOTNOTES:
[209] It is particularly remarkable that if under these circumstances a
rabbit bolts and, seeing the sportsman, doubles back into its burrow,
being then certain that the sportsman is waiting, it will usually allow
itself to be slowly and painfully killed by the ferret rather than bolt
a second time. This is remarkable because it proves the strength of an
abiding image or idea in the mind of the animal.
[210] See Watson's _Reasoning Power in Animals_, and _Quarterly Review_,
c. i., p. 135.
[211] See especially Jesse, _Gleanings_, &c., iii., p. 206; and
_Quarterly Review_, c. i., p. 135.
[212] Thompson, _Passions of Animals_, p. 368.
[213] _The Rat, its Natural History_, p. 102.
[214] Mrs. Lee, _Anecdotes of Animals_, p. 264.
[215] Jesse, _Gleanings_, &c., ii., p. 281.
[216] _Reasoning Power in Animals_, p. 293.
[217] _Loc. cit._
[218] Jesse, _Gleanings_, iii., p. 176.
[219] _Introduction to Arctic Zoology_, p 70.
[220] Dr. Henderson, _Journal of a Residence in Iceland in 1814 and
1815_, vol. ii., p. 187.
[221] _The American Beaver and his Works_ (Lippincott & Co. 1868).
[222] To obviate this possibility, they often select as their site a
place where a spring happens to rise in the bottom of the lake or pond.
[223] In times of considerable 'freshet' the former case sometimes
occurs; the beavers not being able to provide for a very considerable
overflow through their dams, the latter become then wholly submerged.
When again exposed, the animals take great pains in repairing the
injuries sustained.
[224] Note on Beaver Dams (_Proc. Boston Soc. Nat. Hist._, 1869, p. 101,
_et seq._).