Popular Science Monthly/Volume 77/August 1910/Instinct and Intelligence in Birds III
|INSTINCT AND INTELLIGENCE IN BIRDS—III|
By Professor FRANCIS H. HERRICK
IN earlier papers we have tried to show how the behavior of wild birds is moulded upon instinct and how some of their instincts have been modified on a large scale, or specialized in a peculiar manner. We shall now examine the other side of the shield, in order to ascertain how intelligently they work, and in relation to their intelligence it will be necessary to consider the growth of the young, and the development of certain instincts, more particularly that of fear.
Many birds, like some mammals, have been lauded by idealists, as paragons of virtue, and endowed with all the human or even angelic powers of intelligence and reason; others, again, have regarded them as the slaves of a blind or stupid instinct, whose lives are stereotyped, and run in grooves, determined largely by heredity. "Do not speak of blind instinct," says Michelet, the historian, "facts demonstrate how that clear-sighted instinct modifies itself according to surrounding conditions; in other words, how that rudimentary reason differs in its nature from the lofty human reason." "Through the thick calcareous shell, where your rude hand perceives nothing," the bird-mother "feels by a delicate tact the mysterious being which she nourishes and forms. . . . She sees it delicate and charming in its soft down of infancy, and she predicts with the vision of hope that it will be vigorous and bold, when, with outspread wings, it shall eye the sun and breast the storm."
While we are not over-zealous in applying the rule of parsimony, like most modern students, we are compelled to take-a middle course. When the degrees of intelligence can be more justly weighed, the mental powers of birds, as well as of mammals, will be better understood. At present the balance does not seen to swing very far on the side of intelligence. It is certain that the instincts of birds are modified at every step by association, and that the automatism of habit is quite as striking as that due to heredity, which it sometimes replaces. Many birds learn readily from experience; some remember long, when past experience serves as guide to future conduct. It may well be doubted if they ever attain to the level of analogical reasoning, or of deliberately inventing the means in order to attain a definite aim.
Every observer is no doubt unduly influenced by the force of isolated facts, and too often falls into temptation by trying to interpret them without a full knowledge of their history. The act in question may appear irretrievably stupid or exceptionally intelligent, while upon fuller knowledge, either view might prove wholly erroneous. Illustrations could be multiplied, but the few which follow, may be of interest.
Shrike Impaling Prey.—The great northern shrike is well known to impale its prey, such as grasshoppers, small birds and rodents, on thorns, and it presumably returns to them when in need of food, although I am not aware that the bird has ever been actually seen in the act of reclaiming its booty. According to some accounts the shrike impales its prey in order to rend it with the greater ease, but still goes on killing after it has satisfied its appetite.
On April 8 of last year I happened to witness a futile attempt at impalement under such favorable conditions of seeing all that transpired, that any mistake as to the meaning of the actions would seem to be impossible. A harsh piercing cry attracted my attention to the bird, which almost at the same moment dived into the stubble of an adjoining field, and came up with a large object in its bill. Fortunately it flew directly towards me, and alighted on the bare, lower branch of a maple tree, less than ten feet from my eye, as if completely preoccupied, and indifferent to observation. I could now see plainly that it held a little shrew, about three and a half inches long, and in a strangle grasp by the nape of the neck, for the body was as limp as a rag. The shrike at once proceeded to walk along the branch and try to impale the rodent, extending its head and drawing the body of the animal in a peculiar manner, against the soft twigs of the tree. It tried the terminal twigs, and the equally soft lateral shoots, and went through the same motions on two different branches. After several minutes of this ineffective effort, with a loud rasping call of a different character, it flew off in the direction of some woods, and was seen to descend to the ground.
The interpretation of such behavior seems obvious—that the shrike, when under the spell of a strong impulse, does not know a thorn-bush from a maple tree. Must it try tree after tree, until one of the right sort is found? If it can return to its tree by memory, why can not it find one suited to itsby intelligence; or, was this a bird with inherited instinct to impale, but with no previous experience with thorns?
Robin "Tying Knots."—So far as I have observed, the robin in nest-building, ties no proper knots, unless the present case (Fig. 23) be exceptional, although strings are coiled more or less effectively about adjoining twigs. This nest was placed in a crotch of a pine tree, and one of its supporting branches bore the peculiar double loop or "knot" which is here shown. It seems that a piece of string over two feet in length was brought to the nest-site, and passed five times round the larger, and twice about the smaller of the two twigs, with overlaps due to working each string-end independently. Having thus fixed it firmly at the middle, the intelligent course would have been to have incorporated the loose ends with the nest. Instead, they were both left flying free, so that this labor, however begun, was not intelligently finished. The eighteen' inches of free string really served to render the nest conspicuous.
Woodpecker Drilling for Insects.—While in the Maine woods on August 13, my attention was drawn to the freshly drilled hole of a
Fig. 23. Double "Loop-knot" made by Robin about Pine-branch close to its Nest, illustrating an act probably instinctively begun, but not intelligently finished, since the ends of the twine were not incorporated with the structure, but left hanging free.
woodpecker (Fig. 24), in a pine tree, which was two feet in diameter at the base, and apparently sound. This hole, which was remarkable for its size, had been cut at a point seven feet up, through nearly five inches of solid sap wood, to the heart of the tree, and was 93 inches long, 51 inches wide, and 8 inches deep. These dimensions would imply the removal of over three hundred cubic inches of wood, and the chips, some of which were four inches long (Fig. 25), were plainly the work of our largest northern species, the pileated woodpecker or log cock.
A moment's inspection showed that this woodpecker had tunneled
Fig. 24. Huge boring of Pileated Woodpecker in a white pine two feet in diameter, to reach galleries of the carpenter ants, seven feet from the ground, where the insect gained entrance; illustrating either instinct to follow sounds, or intelligence in adapting means to end.
Fig. 25. Sound Pine Chips from Workshop of Pileated Woodpecker, shown in Fig 24; some are bent or broken with the wrenching stroke of the bill. Natural size.
to reach the big carpenter ants (Camponotus herculeanus), which had extended their galleries up into the tree's heart, and some of which were already entrapped in the exuding pitch. Now one of the chief points of interest in this case was that the ant-borings were few, and the tree itself so large and solid that it would seem to be impossible for any bird to detect their presence by sounding with the bill. On the opposite side at the base, a long ant-hole was plainly seen, and at this point the observations of the woodpecker had evidently begun. A few feet above this opening it had attacked the harder wood in three different places, but desisted after making wells a few inches deep. The woodpecker then went up seven feet, where the wood was presumably softer, and made the drilling, which led to success. With these facts only known, this might appear like a case of reasoning by analogy, but there is still one sense unaccounted for, that of hearing, for the olfactory sense must be ruled out. It is possible, or even highly probable that such birds either instinctively or habitually follow the sounds in wood—sounds of wood-borers at work—and unless it could be shown that the boring of carpenter ants cannot be heard through five inches of solid wood, I should be inclined to accept this view.
This case suggests another practise of woodpeckers, the interpretation of which is clear. The president of a large university recently compared the futile efforts of certain reformers with these of a flicker which was seen to be repeatedly engaged in the vain attempt to "drill a hole through a copper gutter." The comparison may be apt to point a moral, but is a trifle unfair to both the instincts and intelligence of a useful bird, which will drum on any resonator, either to call its mates or for the pleasure of the sound, and by habit will come to the same place daily for more than a week, as in a case which we recently noticed. In this instance the resonant body was the roof of a bird house, one shingle thick, to pierce which, had that been its object, one or two blows of its strong bill would have sufficed.
II. Intelligence in Young Birds
The dawn of intelligence in young birds is seen, as we have earlier shown, through the inhibition of the food-response by association—association with the parent, the nest or the vibration imparted to the tree by the touch of the parental foot.
For the first twenty-four hours, or longer, the altricious nestling behaves like a mechanical toy, and in relation to the food-response is a well-nigh perfect reaction-machine. It responds to every kind of a tactile or auditory stimulus, and within the limits of fatigue its responses are about as uniform and predictable as those of an electric bell. Remove the blind and naked cedarbird from its nest, and the complex food-reaction is given as regularly and as continuously as before (Fig. 26). By the second or third day, however, all this has changed, and it is difficult to get any food-response if the bird be out of its nest with which association has become established. If the young are not removed, however, the feeding reaction is usually regularly given, unless checked by satiety or the rise of the instinct of fear. Association in the early life of young birds thus tends, as we have seen,
Fig. 26. Young of Cedar Waxwing, blind and naked; but little over twenty-four hours old: a, typical prone position, when at rest; b, typical food-reaction, or reflex response to sound or contact-stimulus.
to cut out a lot of useless reactions, and to limit their responses to those which count.
Growth in Relation to the Development of the Instincts and Intelligence.—We have used the term "instinct" as synonymous with compound reflexes, that is, as reflexes involving relatively complex coordinations of the muscles and other organs. Although the sign or manifestation of an instinct may be suddenly given, the instinct itself, like every other power, seems to be unfolded gradually, and in correlation with the organs upon which its action depends.
In many precocious birds, which run, swim or fly at birth or shortly after, some of the instincts are relatively perfect at the moment of emergence from the shell, or according to certain observers even before this event, as when the young, which remain for hours with the shell chipped, are thought to respond instinctively to the warning cries of their parents. In rare cases, as in certain megapodes, they are born masters of their own destiny, and receive no care from parents which they never see. At the other extreme stand the common altrices, like the robin or cedarbird, which are blind at birth, and so helpless that they would shortly succumb without that parental care and protection which is so faithfully rendered. Growth and development are continued after hatching, but under new conditions, and at the age of two weeks, when the nest is commonly deserted, the young so far as instincts and intelligence are concerned are at about the same stage as many of the precoces at birth.
Between these extreme types every intermediate stage is found. The American black and yellow-billed cuckoos have a place near the middle of the series, but as we have already seen, they are exceptional in many ways, not alone in the possession of great muscular strength, but in their equally remarkable muscular control, being able to grasp
Fig. 27. Growth-curves of the Cedarbird and Black-billed Cuckoo, as represented by the daily increase in body-weight from hatching to flight from nest, illustrating an initial stage of relatively slow growth (in cedarbird first to third day), a period of maximum increase (third to ninth day), and a final stage of retarded growth or shrinkage in weight. See table.
a twig, and with both feet pull themselves up when but four hours old, or possibly less. This ability is closely related to the climbing stage which is entered on the seventh day, when they leave the nest in succession, and ascend into the branches, where they remain for a period of two weeks before ready for flight.
In the cuckoo the curve of growth, as indicated by body-weight, appears to be quite even and regular after the beginning of the second day (Fig. 27). In these particular birds the highest rate was registered on the third day, and this proceeded without appreciable interruption until the last day in the nest, when it was slightly checked. The power of muscular coordination, association and the instincts of fear and of preening seem to develop gradually after the first day. Thus the initial attempt to preen, which involves the complicated act of drawing the mandibles over the feather-tubes, may be witnessed on the fifth day; thereafter it is repeated more and more frequently, until on the sixth day it is an established practise, and the movements have become very precise. Gradual also is the development of fear, an early premonition of which is crouching and hugging the floor of the nest, although its final manifestations, such as bristling and spreading, giving a high-pitched alarm, or jumping out of the nest, may seem to mature suddenly, partly no doubt because the stimulus which provokes them is suddenly received.
In the altricious cedarbirds, a single family of which was weighed and measured in 1901, there was (1) an initial period of relatively slow growth, lasting three days, followed by a second period (2) of
Fig. 28. Growth-curves of the Black-billed Cuckoo and Cedarbird, based on daily increase in length of wing from hatching to climbing stage or flight. See table.
maximum increase, of six days, and a final interval (3) of fluctuating or retarded growth, extending from three to six days before flight, the birds even losing weight either before or after this event.
The growth-curve of the most vigorous member of this cedarbird family (Fig. 27), the first to hatch and to fly, is seen to start with a higher initial rate, and to maintain it from the third to the ninth day, at the age of flight. Fortunately this bird, which was then lost, was recaptured on the fifteenth day, when it is seen to have shrunk very perceptibly. It had, in fact, lost nearly three grams, or seven per cent., in body-weight. The curves showing the rate of wing-growth in both cuckoo and cedarbird (Fig. 28) follow those of body-weight very closely, but there is possibly a variation in other organs, such as the leg or tarsus, but it is difficult to obtain reliable measurements on some of these parts. The most vigorous nestling (No. 1) more than doubled in weight on the first day, more than trebled on the second, and more than quadrupled on the third, while on the twelfth day, when it left
Fig. 29. Young Cedarbird, No. 1 of table, shortly after hatching, lying on side, cicatrix of umbilicus showing on abdomen; weight 5 grams. August 10, 1901.
the nest it had increased its initial weight seventeen-fold. What ten days will do for the young cedarbird on the score of appearance may be seen by comparing Figs. 29 and 30, the first of which shows nestling No. 1 when about two hours old. The data on which these curves are based are given in the following table.
Fig. 30. The same Cedarbird (on left) as shown in Fig. 29, ten days later with birds Nos. 2 and 3 from the same nest. All show the crouching tendency, in evidence of fear.
Kuhlmann,The Psychological Review, Monograph Series, No. 44, November, 1909. who has recently published an interesting study of the development of the instincts and intelligence in certain altricious birds, in particular the turtle dove, the brown thrush and the red-wing blackbird, finds the rate of growth quite similar to that shown for the
Growth-records in Cedarbirds and Cuckoos, from Hatching to Flight, or Climbing Stages
Cedarbird No. 4 was probably starved by its more vigorous mates, after the second day. Cuckoo No. 2 fell out of its nest. "0" indicates the egg.
cedar waxwing, and has based his results upon a much larger number of cases. He also considers that the three stages enumerated correspond to stages in the development of muscular coordination, of association and the instinct of fear. During the first period, when the power of motor coordination is weak, according to this observer, "the first crude discriminations and associations are made," and the first signs of instinctive fear noted. In the intermediate period (fourth to seventh day), discrimination improves, and association is perfected, while from the beginning of the last period "there is an abrupt change in all the reactions, the food-reaction ceasing for all the artificial stimuli, excepting occasionally for the visual, and fear begins to develop rapidly through several forms of manifestations."
Kuhlmann recognizes five different manifestations of fear, beginning with "cessation of the food-reaction to stimuli that at first aroused it," and ending with "escape from the nest when approached." Discrimination and the formation of associations between the food and certain stimuli are thought to develop simultaneously, and "all stimuli with which no pleasant associations are already formed are then at the same time instinctively feared." The food-reaction is not only modified by association, but is inhibited by fear, and while the development of association is gradual, the passage of one manifestation of fear to the next in order is often very abrupt. Such animals, he says, "come to fear particular things not so much because of unpleasant associations that are connected with them, as because the taming process has not been completed."
We can not accept the conclusion of the writer quoted above, that "fear for particular things remains in the main instinctive." Fear and association, as we have seen, are without doubt developed, like all else, by a gradual process, however abrupt certain reactions of fear may appear. The normal and usual reactions of daily life seem to go through a sifting process; the usual pass readily through the sieve of experience and are stamped as harmless by association, provided they are really harmless, or at least not disagreeable. Further, there seems to be left a residue of strange or unusual sights, sounds or tactual stimuli, ready to produce the fear manifestation, at a moment's call, when this particular stage in the developing instinct has been reached. The reaction is instinctive, but in no true sense would it seem to be the inherited fear of any particular object or thing. Fear of objects having particular, inherent qualities, which are harmful or unpleasant can come only from experience of their harmful or disagreeable effects.
Habits of Young Kingfishers.—In my work on "The Home Life of Wild Birds," I have described some curious habits which kingfishers show when taken from their underground nest at an early age, especially the habit of sitting still, and of walking backwards. The earlier observations were made over ten years ago, and thinking that some other questions might be involved, such as the rising instinct of fear, experiments were repeated on another family of these birds in the summer of 1908. When dug out of the ground on July 8, the five young in this case were found lying twenty-eight inches below the surface, at the end of a six-foot tunnel; they were in "pin-feathers," and according to my estimate about eight days old. Experiments were made on the ninth, fourteenth, twentieth and twenty-third days, when the young were at an age approximately corresponding to the date, with the following results; fear did not seem to play any part as a disturbing or inhibitory factor in their behavior during the first two days; they would go forward or backward, rather indiscriminately, whatever their position might be with reference to the observer, and whatever the nature of the surface upon which they were placed. On subsequent days, the tendency to walk backward increased, and though fear was rising, they were readily quieted, and when placed in certain positions they would sit quiet for long intervals.
The following notes were made on the behavior of these kingfishers on the last day of observation, July 23; when placed on the pine carpet, all began to make off with fluttering wings, going forward with crests erect and rattles sounding. When recovered and placed in line, they soon quieted, and the backward walking movements began (see Figs. 31 and 32). All showed the same tendency, and one, in which it was especially marked, would retreat four feet before the camera could be focused, and this was repeated for the twentieth time. The same performance was given on level ground, or an incline, and whether facing the observer or away from him, though with variable movements in many
Fig. 31. Five Kingfishers about twenty-three days old, removed from underground and placed in line, to illustrate habit of keeping still, and of walking backwards.
Fig. 32. The same Kingfishers one minute after the position assumed in Fig. 31 was photographed, showing that Nos. 1 and 5 have each taken a few backward steps, while the pose of Nos. 2 to 4 has not appreciably changed.
cases. When placed in head-to-tail line, and in contact, the line would remain unbroken for a surprising length of time, with hardly the turn of a head, which seems to be due to their habit of sitting still, with wings often interlocked, during their long imprisonment in a dark, subterranean chamber. When, after a good rest in this position, they were brought to right-about-face, two immediately moved backward a few steps, and came to rest again (Figs. 31 and 32). Move around them in circle, and not a head is turned; make a pass of the hand suddenly towards them, and sometimes there is a slight backward movement, but sometimes there is none; reverse again with heads turned away, and two turn part way around, one of which repeats the movement when repeatedly reversed. If placed on their backs, they will slowly right themselves, though if in the nest-hole they were sometimes contented with this position for a longer time.
I am now convinced that the earlier conclusion was correct, and that the peculiar actions described are due to habit, learned underground, and in relation to getting their food, although I was probably in error in supposing that their instinct of fear was ordinarily delayed until they were ready to leave the tunnel. When such birds are handled daily there can be little doubt that this instinct is liable to be checked. The arched chamber of sand in which these kingfishers lay was 111 inches in diameter, and 61 inches high, while the tunnel leading to it had a 3-inch bore. Its temperature stood at 77° F., and was seven degrees cooler than that of the air outside. Since these five birds were each about six inches long it is evident that they were closely packed, and that once in the tunnel, no turning movement would be possible, any more than for the adult which after feeding always backs out of the hole. Now we have earlier noticed a tendency among the older young to crawl down the passageway, and meet the parent at the mouth, but that they are hustled back and presumably fed at the nest, hence the probable association between walking backwards and getting food, and hence the curious habit displayed by these birds when they are taken from the ground.
III. Intelligence in Adult Birds
There seems to be little intelligence displayed by birds in regard to the quantity of food served at the nest. What one of the altricious kinds really does in effect is to "test" the reaction of the throat of its nestling, and to await the response. If this is not forthcoming the food is quickly withdrawn, and another is tried. The most responsive bird gets the food, and there is no distribution on any other basis than this. The same bird may thus be fed twice or even three times in succession, the strongest usually getting the most, and the amount which it can take being reflexly determined by the gullet.
On the other hand, intelligence is certainly shown in the kind of food served, and in the treatment which it often receives. Thus a gull chick when but a half-hour old gets only small bits of predigested fish, but at the age of three weeks it may be invited to bolt an entire squid. Again a bird like the black-billed cuckoo, which has repeatedly tried to serve a large insect and failed, has been seen to quickly withdraw it, mince it fine with her bill, and then offer it with success.
Birds quickly acquire a habit of going to their nest, by a definite path, through association, and if the branch which holds it is suddenly removed, they try to follow the established course, and will hover at the point in space which the nest formerly occupied, even when their young are in full sight, and these actions may be repeated many times, until the old habit is broken by an actual visit to the new position (compare
Fig. 33. Flicker feeding Young, with nest-hole opened at the back, illustrating the force of old habit. The bird for some time continued to enter the hole by the usual course.
Figs. 33 and 34). The habit of entering the nest from a certain side, of facing the same way while sitting over the eggs, of grasping the same branch when inspecting and cleaning the nest, and of leaving it in a definite manner, are all more or less fixed by habit in a brief course of time. In the same way drinking and bathing places, perches, spots for dusting, sun-bathing and sleeping are resorted to by habit for longer or shorter periods, according to the other conditions which modify behavior.
Do birds discriminate their own eggs and proper young? Very many do not, yet some do, sooner or later. The success of the European cuckoo and the American cowbird, the young of which are reared by foster-parents of many diverse species, would argue for little power in this direction. Yet, in some cases, the foreign body is promptly removed, when the nest is not summarily deserted through fear.
The freedom with which certain finches and grosbeaks learn to imitate difficult notes, and the fair degree of precision with which some
Fig. 34. The same Flicker as shown in Fig. 33, after new habit of entering opened nest was formed.
of the parrots, crows, jays, jackdaws and magpies reproduce spoken words, or even short sentences, show that they readily discriminate differences in the pitch of sounds, although they do not possess a cochlea of the complexity of structure found in mammals, and it is the cochlea in which this power is supposed to reside in man. It is interesting to note that the magpie, though a star performer in this art, never exhibits it, according to Blackwall, in a state of nature.
The bower birds of Australia show a decided liking for bright and colored objects of various kinds, which they work into their remarkable "runs," bowers, or "play-houses," and the crow, and other members of his tribe, which are commonly regarded as the most intelligent of birds, can seldom be trusted in the presence of any small and shining objects whatsoever, which they will steal, and either carry off and hide, or work into their nests. To mention a trivial case—a tame young crow once entered my room, made off with some objects on the dressing table, and deposited them on a belfry-roof hard by. Again, the hooded crow in Egypt and India, where from a long and undisturbed intercourse with man, it has come to build its nests in the city streets, and in Cairo even before the foliage of the lebbek trees is out, often gives free rein to this propensity, as was well shown by the experience of an optician in Bombay, who lost a large store of steel spectacle-frames, and later found them in a ruined state, worked into a nest of this familiar bird. The propensity to seize bright objects, and to hide and store food by burying it in the ground, a practise attributed to the European crow, raven, magpie and rook, is undoubtedly instinctive in origin. Their ability to find it' again would depend more upon intelligence than in the dog, which has the same tendency, for they are presumably without the guiding power of scent. The Californian woodpecker (Melanerpes formicivorus) is noted for the autumnal stores of acorns which it embeds in the bark of trees, but the strong instinctive impulse which shapes its conduct is accentuated by the reported fact that the holes so nicely drilled are occasionally filled up with stones.
That color plays an important part in the lives of birds seems highly improbable, although it is a commonplace fact that the nest in many cases harmonizes perfectly with its surroundings. For several seasons I made a practise of offering colored yarns, such as blue, brown, green and bright red, to various species of birds, for building purposes, and especially to robins and cedar waxwings; as a rule, all colors were taken indiscriminately, with very bizarre nests as a result. When white threads or long streamers of cotton cloth were added, these were usually taken first, and in greater quantity, apparently because they were more conspicuous, and sometimes to the detriment of the builders. Thus, one of the least flycatchers took and dropped so much of the cloth that a white trail was finally laid from field to nest, in the construction of which five times more was used than needed. The quaint structure which resulted was too obvious to escape destruction, and it did not endure many hours.
The docility of birds is well illustrated by the trainer's power over many species, and by the tricks which, through a system of rewards and punishments, they can be made to perform. A classical illustration is furnished by the art of falconry, the popular sport of middle-age Europe, in which the young of the wild peregrine falcon, or of some other hawk, was trained to limit its instinct to kill to a particular kind of game, to follow the falconer afield, to stoop to the quarry, and return to its master's call. After a similar fashion the instincts of the cormorant have been molded to the will of man, and successfully used in taking fish, a practise which I am informed may still be witnessed in certain remote fishing communities in Japan, the trained birds descending from father to son.
Modern experiments in the laboratory, which have been conducted by students in recent years, by the Hampton Court maze or labyrinth method, upon young chicks, and various wild species, show an ability to learn more or less rapidly, according to the simplicity of the path to be traversed. They always seem to be guided in large measure by sight. Their educability has been further tested by Thorndike and others, by placing food within sight, but enclosed in a wire box, access to which can be reached only by working some simple contrivance, with bill or foot, such as pecking or pulling at a string. The animal is thus induced to do an unusual thing, or to do it in an unusual way, but some species, like the house sparrow, have proved apt to learn, and though success may come first through accident, by the tenth or some later trial, the new act is learned, and unnecessary movements are in time eliminated. The effect of the acts performed, as in the case of exit from the labyrinth, is remembered for days or weeks, according to the strength of the habit, or the ability of the learner. Whether the memory involved in these and similar acts is of a visualized character, involving a memory idea, image or picture, may be doubted, though Edinger among others is not inclined to admit this. We might ask why a bird, with a memory image of the position of her nest, does not always strike a direct path to it, after reaching her tree. Why should she slavishly follow the track stamped in by previous associations, walking along a certain branch, and grasping a certain twig, before landing at the nest-side, a practise very commonly followed? Such behavior certainly can not always be attributed to the inhibitory effect of fear.
All the intelligence which birds may on occasion exhibit seems to give way under the spell of any of the stronger instincts, as when the male canary, as related by Blackwell, plucked the feathers from the necks and backs of its own young in order to line a newly built nest, although ether feathers were supplied to it in abundance. They seldom meet emergencies by doing the intelligent act, and, in spite of the anecdotes, probably but seldom come to the effective aid of their companions when in distress. On the other hand, I have more than once seen a mother bird try to pluck a hair or piece of grass from the mouth of a nestling.
It has been asserted that only birds can be frightened from fields by scarecrows, but to most birds any strange object is a "scarecrow," which may in time, and often brief at that, become familiar through association, as shown by the many devices used by farmers to frighten crows from their fields of newly planted corn. The genuine scare crow is a subject worthy of further study.
At this point I wish to notice certain anomalous actions of peculiar interest in birds, and to refer particularly to the wood swallows (Artamidæ) of Australia, the hornbills (Bucerotidæ), of the East Indies, and to the honey-guides (Indicatorinæ), of the East Indies and Africa. The wood swallows are social, gregarious birds of rather small size, characteristic of the tropical forests, where they feed upon insects, and often "hawk" them, like the swallows and swifts. Many have the curious habit of "swarming," or clustering in cold or wet weather in sheltered places or under trees, possibly for the purpose of keeping warm, though this appears to be an assumption; when thus bunched, they crowd one upon another, all heads up, thus forming a great ball-like mass several feet in diameter; if disturbed they go off with startling effects produced by the whirring of many wings, often leaving, it is said, a few dead ones behind, which might have been smothered in the press. All this is suggestive of rheotropism, or the tendency shown by many fish, insects and other invertebrates to orient themselves in response to currents of air or water, and in particular of the clustering tendency shown by the young of many aquatic animals, as well as by many flying insects. Whatever its history may prove to be, no one can doubt that the act is purely instinctive in origin. We are reminded of the swarming habits of chimney swifts, which have been known to enter hollow trees in great numbers for the purpose of roosting and passing the night, especially after their arrival in spring and before their fall departure.
Hornbills are large birds of peculiar structure, and wide distribution in the old world, being noted for their great serrated bills, which in many of the species are surmounted by a remarkable casque or helmet. But it is in the cyclical instincts of their reproductive period that we find the most extraordinary departure from the common type. Before she is ready to lay her eggs, the female hornbill enters some suitable cavity, in a dead tree or branch, and with or without the assistance of the male, proceeds to wall herself in, closing the opening with mud or excreta, or with both, with the exception of a hole large enough to admit the bill, and the food which is passed in by the male. While thus confined, the female lays the eggs, incubates them, and through the cooperation of her mate their naked and helpless young are reared until ready for flight; then the prison-house is suddenly burst open, the enfeebled mother and the young are liberated, and the happy family united in the bright world outside. Further, at intervals during this period the male casts off and regurgitates an inner layer of the gizzard, which with all the contained food comes up like a dumpling, that is to say, a package or thin-walled sac, three inches long by two inches in diameter, and upon this generous food-supply the female is able to subsist for some little time.
The practise of closing the opening to the nest is to be regarded as a modification of the nest-building instinct, and while its history has no doubt been lost in the remote past, it may be compared with a not wholly dissimilar practise of the European nuthatch, which also nests in natural cavities, and when the entrance is large regularly blocks the passage with mud until it will barely admit her body. The hornbills have possibly lost the cleaning instinct, if they were ever possessed of it, and the singularity of their present activities must be attributed to instinct alone.
The little honey-guides are related to the barbets, and hoopoes, rather than to cuckoos, although like many of the latter they are thought to regularly steal the nests of other birds, and never rear their proper young. But aside from this diversion, they are said to conduct the passing traveler to bees' nests, to call his attention to the important business in hand by hisses and shrill cries, and to even fly in his face "as if enraged at not being followed." That such efforts are not wholly altruistic may be gathered from the fact that they will eat the bees, grubs and honey alike. According to the accounts, the honey-guides are the "pointers" among birds, for when the woodsman is encountered, they flutter up to him and point the way to a nest, and if followed, go on and on, but halt when hot on the trail. They will also point to empty nests, or even to a domestic hive, but more significant than this, they will follow a dog, or lead the confiding traveler to a leopard, cat or snake, showing clearly that, whatever the origin of this practise, whether concerned with the instinct to sound the alarm at a common enemy, and to follow it and keep it in view, or not, we are dealing with an instinct; and probably one of very pure type.
We will close this account by giving one or two reputed instances of bird-intelligence which stand out in a marked degree from others of their kind, on account both of the acts themselves and the credibility of the witnesses. Thus Montagu, whose excellence as an observer is abundantly proved in his "Ornithological Dictionary of British Birds," states that he once saw two crows (Corvus corone), by the seashore "busy in removing small fish beyond the flux of the flowing tide, and depositing them just above high-water mark, under the broken rocks, after having satisfied the calls of hunger." It seems to me that too much has been made of this instance, since it may with equal justice be interpreted as an illustration of the instinct to hide, the circumstance of the tide being fortuitous, for it does not follow that these birds knew that the tide would surely advance and sweep away their prize. The incident, however, is interesting in relation to another, told of the hooded crow (Corvus splendens), by the worthy Blackwall, who saw these birds "on the eastern coast of Ireland, after many unavailing efforts to break with their beaks some of the mussels on which they were feeding, fly with them to a great height in the air, and, by letting them fall on the stony beach, fracture their shells, and thus get possession of the contents." Perhaps it would not be easy, says Blackwall, "to select a more striking example of intelligence among the feathered tribes than this, where, on one expedient proving unsuccessful, after a sufficient trial had been made of it, another was immediately resorted to."
A similar habit has been attributed to the gull, but with how much truth I am unable to say ; the exact history of its origin, in either case, would be of much interest. It would seem to have arisen either from accident or from ideas, for the question of imitation can here be ruled out, so far as the initial performance in a given individual is con- cerned. The very rarity of the habit, attested by the fact that it has been so seldom reported, seems to clearly point to an accidental origin, and to the conclusion that it does not rise above the level of associative memory.
- See also "The Relation of Instinct to Intelligence in Birds," Science, N. S., Vol. XXVII., 1908.