Popular Science Monthly/Volume 36/April 1890/Intelligence of Squirrels
By Dr. T. WESLEY MILLS,
PROFESSOR OF PHYSIOLOGY IN MCGILL UNIVERSITY.
UNTIL recently, the habits of animals seem to have been considered simply as interesting manifestations of their life, but without any special reference to their relations to the intellectual part of the creatures concerned. But unless we assume that animals are devoid of mind and true intelligence—an extreme and untenable position—there must be a possible science of comparative psychology, as there is of comparative anatomy and physiology. The study of animal intelligence is possible, interesting, and important, whether we regard man as derived from some lower form, and his intellectual as well as his physical being the result of evolution; or whether we consider that man stands wholly apart in origin either as to body or mind. In the latter case, the study of the lower forms of mind affords a useful contrast with its highest development as seen in man; in the former, we aim at the construction of a ladder by which we may climb from the simplest manifestations of consciousness to the highest performances of the most gigantic human intellect.
I have selected the study of squirrel psychology as the subject of this paper, because so little seems to have been written on the subject; because these animals are open to the observation of every one; and chiefly because I have been able to give special attention to them myself. Their habits will be considered principally, but not exclusively, from the psychological standpoint; and I shall apply the comparative method, making such references to the habits and intelligence of other rodents as seem to throw light on those of the squirrel. While some attention has been paid to other species of squirrels, my studies have been chiefly on the ground squirrel (Tamias Lysteri) and the red squirrel (Sciurus Hudsonius).
These species, in many respects, form a contrast to each other. The chipmunk, chipping squirrel, or hackee, has his abode underground in a specially constructed burrow; the red squirrel, or chickaree, lives in nests in trees; and the intelligence of the latter seems to be altogether of a much higher order than in the ground squirrel. This was abundantly illustrated in my experiments with an ordinary wire rat-trap having a spring door. The trap was scarcely laid down near the haunts of the chipmunk before one entered it, in fact before my eyes; and there was never any difficulty in securing as many as were wanted. On several occasions, when one had escaped in the room, on placing a small apple in the cage, the creature re-entered it almost at once.
Very different was it with the red squirrels; at first they entered the trap, hut not afterward. They approached it, sometimes two or three together, ran round it on the upper rail of the fence on which it was placed, or sat on top of it in short, did everything but enter it—all the while seeming to enjoy the whole greatly.
Having secured a couple of ground squirrels in the manner described, I kept them under observation for the period during which they survived, viz., one for about a month and the other for between two and three months. From the first, one of them seemed to take more kindly to his new surroundings than the other; one appeared shy and dull, while his fellow seemed as happy as any chipmunk might be. They were captured in September, and it has often occurred to me that their habit of hibernation had something to do with the behavior of the one, though we should expect that, in such a matter, both would be equally or considerably affected. The degree to which, while retaining their original habits, the latter became modified in confinement, furnished me with an interesting study, and suggested many problems. My experience does not agree wholly with that of Audubon and Bachmann, who say, in their "Quadrupeds of North America," "We are doubtful whether this species can at any time be perfectly tamed." The one of my chipmunks that survived longest became in a short time so tame that he would eat from the hand, and even looked to be fed in this way. True, any noise, or any unusual movement, might startle the creature, when he would make the quick dart away so characteristic of the species in the wild state. But from this he very quickly recovered, and the tendency to be thus frightened grew less and less. The authors referred to also state that "they appeared to have some aversion to playing on a wheel, which is so favorite an amusement of the true squirrels." This does not at all agree with my observations; for though at first my chipmunk was apt to be startled when he found the revolver of his cage moving on his entering it, he soon got used to it, and delighted in it as much as any squirrel could—in fact, he used it by night and by day, manifesting an ability to control it which speaks much for the readiness with which such animals adapt themselves to new and difficult movements, and which shows how highly developed those parts of the brain must be which are concerned in the balancing and kindred functions. I may here correct another statement of the same authors. They maintain that squirrels do not lap fluids as the dog and cat. From repeated observations I know this to be an error, at least so far as the ground squirrel is concerned.
It has usually been assumed that squirrels, and indeed most rodents, feed wholly on vegetable food, and that in those instances in which the contrary has been observed there was evidence of a perverted or morbid appetite. Audubon and Bachmann, however, state that the flying squirrel (Pteromys volucella, Des.) has been caught in traps baited with meat. A number of writers, especially within the past few years, have drawn attention to flesheating habits in several rodents, mostly under peculiar circumstances. Some interesting questions arise in this connection: 1. In how far is any rodent carnivorous, when abundance of all the different kinds of vegetable food that the animal uses is at hand? 2. What is the relation between confinement and altered appetites? 3. In how far are such altered appetites evidence of morbid or perverted conditions, and in how far simply the expression of physiological needs? The whole subject, I am inclined to think, might be placed on a broad and sound physiological foundation; but, before that can be done, many accurate observations are required, and possibly also many series of experiments. If we may judge by the common house rat, rodents possess unusual plasticity as to feeding and other habits, and not less as regards their mental life. I found that my chipmunk would take a great variety of foods, though the experiment of feeding with meat was not tried. He drank milk greedily.
There is one peculiar habit, interesting from a physiological point of view, to be observed in squirrels in confinement. A writer in "Nature" (vol. x) says, "I have noticed that whenever it [the squirrel] cleans itself, after licking, it sneezes violently three or four times into its fore-paws, then rubs them thus damped over its fur." And this writer raises the question as to whether this habit, which he believes voluntary, was confined to squirrels. He does not mention what sort of a squirrel his own was; but I have noticed this behavior as of most frequent occurrence in my caged chipmunk. It seems to me, on the whole, most natural to consider it a voluntary act of the same character, and possibly for a similar purpose, as cleaning the throat in the human subject, or perhaps even blowing the nose. And I am the more inclined to believe that it is voluntary, from the account given of the flying squirrel, as observed by Prof. G. H. Perkins and recorded in "The American Naturalist" (vol. vii). This writer states that on one occasion his squirrel lapped some ink, but shortly afterward manifested disgust and indulged in violent sneezings. Under these circumstances it is difficult to understand, by anything in our own experience, how the act could have been reflex.
Speaking of the relative intelligence of squirrels, this writer says, "I am inclined to believe that the flying squirrel does not possess as much intelligence as the gray or red or some other species." From the entire account of the flying squirrel given by Prof. Perkins, I should suppose that the intelligence of this species and that of the ground squirrel are about on a par—the explanation of which will be considered later.
A question of much interest to the naturalist and psychologist, it seems to me, is the following, viz., to what extent the intelligence of animals that hibernate has been modified by this process, and in what directions. With regard to hibernation, so far as the squirrels are concerned, there seems to be great dearth of accurate observations; in fact, the same remark applies to the whole subject of hibernation, one of the most interesting in the whole realm of physiology. A number of observations are to be found scattered through the literature, but they are fatally lacking, in most cases, in precision of observation and accurate record of dates. From a short but valuable paper on "The American Chipmunk," in "The Popular Science Monthly" (vol. vii), by Dr. C. Abbott, we are led to believe that the ground squirrel spends some time in his burrow before hibernation begins, and that the food laid up is consumed in part before the winter torpor sets in, and more especially in the spring before a fresh supply is obtained in the usual way. Concerning the winter habits of other species, I have been able to learn nothing from any quarter that definitely settles the question as to whether they hibernate or not. Audubon and Bachmann (loc. cit.) state that as much as one bushel and a half of nuts has been found in a single hollow tree occupied by a chickaree or red squirrel. They also state that this species may have several hoards. From different remarks dropped by these writers, from what I have myself observed, and from the statements of Dr. R. Bell, I am inclined to the belief that the red squirrel and some other species do not regularly hibernate the whole winter through. But whether they hibernate at all, in the true sense of that term; whether they have short periods of hibernation, followed by intervals of consciousness, during which they feed; whether they remain in a condition of partial torpor, with slowing of all the vital processes, and yet not in absolute insensibility and with cessation of respiration, etc. all these questions seem to be as yet wholly undecided.
It has long been known that many cold-blooded animals hibernate and, under altered conditions, æstivate; it is further believed that among warm-blooded animals, besides bats, many rodents and some allied animals hibernate. But, when the matter is looked into carefully, it is found that the term "hibernation" has been used in a loose and very plastic sense by different authors. It is highly desirable, therefore, that writers should state exactly to what extent the animal they describe as "torpid," " hibernating," or "in winter-sleep" deviates functionally from the normal; also, that the exact time of the observations be recorded. There is a certain amount of evidence that even birds, representing the highest type of activity, may possibly hibernate; and that many animals, not usually thus affected, may become so under exceptional circumstances—indeed, that man himself, owing to peculiar states of the nervous system, may pass into a condition ("trance") having much in common with the hibernation of lower animals. I think it is very probable that, when the matter has been fully investigated, all degrees of cessation of functional activity will be found represented, from the normal daily sleep of man and other animals, to the lowest degree of activity consistent with the actual maintenance of life. The flying squirrel is nocturnal in habits and exceedingly active, even in confinement, as Prof. Perkins (loc. cit.) has shown; but during the daytime it seems not to be correspondingly quick—in a condition, in fact, resembling somewhat that of a hibernating animal. The "diurnal hibernation" of the bat is not to be forgotten. I noticed that my chipmunk invariably, after feeding, tucked his head down and assumed a more or less ball-like form highly suggestive of a tendency to hibernation.
There are many questions that arise in connection with this subject, one of which bears directly on the subject of comparative psychology: How and to what extent is the intelligence of animals influenced by hibernation? It may be considered pretty clear that both the ground squirrel and the flying squirrel hibernate, and these are certainly among the lowest—perhaps are actually the lowest—in intelligence of the whole tribe. We know that struggle among higher animals develops mental adaptation and other forms of intelligence, and it is rational to suppose that those species of squirrels that do not hibernate throughout the winter, but endeavor to prevail over their surroundings, as well as to adapt themselves to them, should be more intelligent than those spending a large portion of each year in inactivity.
My chipmunk, during its captivity, under certain circumstances, kept to his original habits—e. g., when a single nut was given him he would eat it immediately, but if several were presented at once he would hide them one by one in a corner of his cage, or, if sufficiently small, pack them away in his cheek-pouches. He did the same with cereal grains. When cotton wool or web-like material was placed in the cage, he manipulated it a good deal, but finally made a bed of it, in which he buried himself out of sight.
Within the last ten years attention has been called to "singing" in certain rodents, especially mice; but from numerous references in the literature it appears that "singing," or something analogous to it, has been noticed in a large number of rodents. The well-known note of the chipmunk, from which it has derived its name, is the only one I have heard from it. After studying a colony of red squirrels for some weeks last summer, I came to the conclusion that they have a capacity of vocal expression much greater than is commonly believed. Their usual "barking," or trilling, seems to be the commonest, the most instinctive, and not largely expressive of anything beyond general satisfaction; but I found that, under excitement, there were many other tones, associated with great complexity of emotion, which I am not prepared to analyze, but which there can be little doubt the creatures themselves employ as a means of intercommunication. Under marked excitement, as the result of repeated interferences, I have heard a red squirrel so mingle tones of a musical kind that a stranger, arriving on the spot, would certainly have been deluded into the belief that he was listening to some bird, or rather to an excited pair of birds. The musical character of this combination, together with its continuity and complexity, would perhaps justify the designation "song." One of the writers on musical mice refers to their singing but little in certain instances, except when excited, which is a point of analogy with the chickaree.
It would appear, therefore, that it is likely that, throughout the order Rodentia, a genuine musical appreciation and executive capacity exists, and in some instances in a very high degree; and that apart from this there is also considerable ability displayed in the expression of states of emotion, at least, by vocal forms. Manifestly, the degree to which animals can express their psychic states—and especially in vocal forms—is a matter of the greatest importance, and I have already elsewhere ("Popular Science Monthly," March, 1887) expressed my conviction that animals have a power of communicating with each other, altogether beyond what has been generally surmised. The subject is beset with great difficulties, and calls for the closest observations.
The reviewer, in "The Academy," of Dr. Oliver Lodge's "Modern Ideas of Electricity" emphasizes the promise implied in the present state of scientific research and mathematical investigation that some great step forward is about to be made. "It is because the scientific world," he says, "knows itself to be on the verge of discoveries as to the nature of the ether, more far-reaching possibly than the discovery of the mode of gravitation, that it lives in a state of suppressed excitement, which hinders it sometimes from further progress or from recognition of the relative importance of recent work"; and lie hints that the century which produced Darwin is now ripe for almost a greater genius than he. A similar tone is sounded in Prof. Lodge's book.