Animal Intelligence Part 34

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 circ.u.mstances 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 circ.u.mstances 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 a.s.sist 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 pa.s.sing 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 circ.u.mstance 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 Ess.e.x, placed a pot of honey in a closet, in which a quant.i.ty 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 const.i.tute an inclined plane whereby to reach the rim. A quant.i.ty 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 a.s.sured 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 gra.s.s, 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 gra.s.s, 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 'Pa.s.sions of Animals,' pp.

235-6:--

The life of the harvester rat is divided between eating and fighting. It seems to have no other pa.s.sion 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 a.s.sociation 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; a.s.signing 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 pa.s.s, 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 pa.s.sage 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 sh.o.r.es of lakes, which, being usually shelving and hard, require some further variation in the structure of the lodges. These, therefore, are of interest 'as ill.u.s.trations 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 const.i.tuted 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 lat.i.tudes lays upon them the necessity of so locating their lodges as to be a.s.sured 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 ill.u.s.tration of the fact that beavers possess a free intelligence, by means of which they are enabled to adapt themselves to the circ.u.mstances 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.