Popular Science Monthly/Volume 76/June 1910/Instinct and Intelligence in Birds I

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THERE is no doubt, as Jevons has remarked, that if ants had better brains than men, they would either destroy the human race or reduce it to a state of slavery, but these busy little workers offer no black or yellow peril to mankind, for they are all headed in the wrong direction. In the social hymenoptera nature seems to have done her best with a nervous system built upon the simple arthropod plan, in which segmentation, begun at a still lower level in the animal scale, is the dominant character of its structure, and instinct the ruling method of its response.

The vertebrate, on the other hand, has a nervous system of not only a higher but of a very different order, in which response has left the beaten track of instinct, and become more and more molded upon experience. Classification of these higher types on the ground of anatomy agrees plainly with classification on the score of behavior, and this agreement is based upon the structure of the nervous system, the chief function of which is to order and control response.

It is to the evolution of the cerebrum that the vertebrate owes its powers of rational response, and the higher we rise in the scale of vertebrate ascent from the bony fishes, the greater the development of the cerebral cortex, and the keener the mind of the animal, or the greater its power to subdue its hereditary tendencies, to make its acts accord with the results of experience, or the needs of the moment, and to anticipate the future.

The instincts used to be regarded as immutable, and are now often spoken of as "stereotyped," but in the use of the latter term there is need of frequent qualification, and habits even by repetition become automatic. The mechanical operation of habits, which is universally recognized, has given rise to the idea that acquired automatism may appear in the descendants as inherited or congenital automatism, that instincts are inherited habits and merely illustrate "lapsed intelligence," or habits from which the intellectual processes through which they were originally acquired have "lapsed" or disappeared. The confusion and absurdity with which this view can invest a difficult question is well illustrated by Eimer's[1] attempt to explain the parasitic instinct of the European cuckoo, which regularly lays its eggs in other birds' nests. Eimer is convinced that the little foundling of a cuckoo has so good a memory of its foster-parents and of the nest in which it was reared, that it is able to make a proper choice of both when it comes to lay its eggs in after life, and further that the experiences of its early youth have "at last become instinctive by inheritance." It can not build a nest because it has never learned how, and if it never builds it can not of course transmit the instinct of nidification. When its original progenitors adopted their piratical methods, they did so with their eyes open, for they acted from "reflection and with design." The male cuckoos are dissolute vagabonds and the females as bad or worse, for they wander about not so much to find nests to steal, as to appease "their insatiable sexual desires."

That some instincts, in both arthropods and vertebrates, have not perceptibly changed from age to age is not to be doubted. As Sidney Smith observed, the wonderful instincts of animals seem to have been given them for the preservation of their species, and that without them they would have long ago perished. He says:

The bee that understands one particular kind of architecture so well, once out of his own special line of business, that of making honey, is as stupid as a pebble stone, and with all his talents only exists that we may eat his labours, while poets sing of them; or he constructs his boasted edifice for an egg of which he knows neither the meaning nor the object, to produce a grub of which he can form no possible conception; whereas man knows the beauty of every brick he lays, or tower that he builds. The bee now builds just as he built in the days of Homer; the bear is just as ignorant of good manners as he was two thousand years ago, or ages ago; the baboon still as unable to read and write as persons of honour or quality were in the days of Queen Elizabeth; but there is no progress among the three B's, whereas now among all classes of men those who can read and write are to be counted by the millions.

We might add that the European cuckoo seems to have been no less adept in stealing nests in the time of Aristotle than it is at this day, and that even among the most rational, adaptable, and most plastic of living beings, in his humblest estate, progress has been but little greater.


In some of the fishes, in reptiles, and more particularly in the birds, we can discern the early if often halting steps of that intelligence which in the highest of the primates was destined to turn the world upside down. We can not attempt to specify with any detail the structure of the avian brain, nor would it be of any use to do so, unless we could award the proper functions to its several parts. While this can not now be done, psychology has already learned some valuable lessons from anatomy, at the hands of such a master as Edinger, and is destined to learn many more. Without doubt, in the future, knowledge of the brain of the fish, of the reptile and of the bird will serve as primers for the understanding of the cerebral cortex.

Edinger[2] has shown that to the primitive division of the brain of the vertebrate (or the paleencephalon), which is the bearer of the reflexes and the instincts, there has been gradually added with peculiar adjustments a newer division (the neencephalon), which corresponds to the cerebrum, in which alone is centered the power of association, and of forming memory images. In proportion as the cerebral cortex increases, the primitive brain recedes, while in a corresponding ratio intelligence rises, and purblind instinct wanes.

A very interesting fact for us, as Edinger has further shown, is that while the cerebral cortex of the bird is more highly developed than in reptiles, the far greater bulk of the brain is mainly due to an enlargement of the primitive division, the parts of which reach a size and proportion nowhere else seen, while at the same time they are very generally connected with the cerebrum. From these facts alone we are warranted to infer that while birds are intelligent and able to form associations of some sort freely, they must be animals in which the instincts are developed to an extraordinary degree of perfection, comparable in large measure with those of the social insects. All this is amply proved by their behavior, and in describing the activities of birds it seems best to discriminate as sharply as possible their instinctive activities from the operations of intelligence, assuming, until the contrary is proved, that their reflexes and instincts pertain exclusively to the primitive division of the brain, as already stated, while the power of association is lodged in the cerebrum alone.

Not only does the bird's brain possess great basal ganglia of which the huge optic lobes are most prominent, but a large cerebellum, and very diminutive, possibly rudimentary olfactory lobes. These facts find their clear counterpart in behavior. Large optic nerves, optic tracts and lobes, are to be expected in animals like the birds, which possess the keenest eyes of any vertebrates known, and which depend so largely upon vision for finding their food and for detecting their enemies and their friends.

The wonderful powers of flight, possessed by birds as a class, may not only be long sustained, as in the golden plover which is supposed to make the journey from Nova Scotia to the West Indies, a distance of 1,700 miles, in a single flight, but is often so rapid that fatal results would follow were the control of direction less precise. Their movements clearly demand an organ for the most perfect coordination of their skeletal muscles, and such is undoubtedly found in their large cerebellum, the action of which is purely reflex. Thus swallows are often seen to enter a barn, where they have their nests, at a perilously rapid rate, through cracks or holes, barely large enough to admit their bodies. Under such circumstances a slight error in muscular coordination would be fatal, and I have found fully grown and presumably young birds lying dead beneath such openings, where it was evident from the wounds received that death was accidental, and due to lack of precision in flight. The common swift also moves with astounding rapidity, as if heedless of consequences, but usually avoids every obstacle in its path, even in waning light. It gathers the materials for its twig nests while darting through the branches of a tree, with barely a pause, as it bends to seize in its bill the twig, which is snapped off by the momentum thus gained. Yet mistakes are sometimes made even by the master swift, and I have known a case where a bird of this kind, and possibly a young one, impaled itself on the sharp point of a lightning rod.

The toothed birds of the Cretaceous period, of which Hesperornis is a type, are known to have possessed a brain more nearly approaching that of the reptiles in form, with large olfactory lobes. It thus seems evident that the olfactory sense has lapsed and become rudimentary in most modern birds. Edinger, however, maintains that since birds possess true, though small olfactory lobes, they must smell, but behavior seems to afford the better criterion in such a case. Whatever the advocates of the eye and the nose may have to offer in the future in regard to the habits of buzzards and other old and new world scavengers, repeated experiment has convinced me that the common birds of the country, can not detect their young at a distance of three feet, unless they either see or hear them. In fact, all of the close-at-hand, "as-near-as-you-hold-a-book-to-read" observation, carried on for the past ten years, some of which is to follow, has been conditioned upon the extremely feeble development, if not total lack of this sense.


The instincts of birds may be classed in a general way as (1) continuous instincts, which are needed for the preservation of the individual, such as preying, flight, concealment and fear, however subject to modification through experience, and (2) the cyclical instincts, which are necessary for the preservation of the race.

By cyclical instincts we mean those discontinuous, recurrent tendencies to action which are serial in form, and which together characterize the reproductive cycle. They may be called, with some allowance, the parental instincts, it being understood that this epithet is used in a descriptive sense, and that there is no one kind of reaction to which the term is specially applied. These instincts recur with clock-like regularity in the spring and summer in the northern hemisphere, and are subject to repetition, more or less complete, within the breeding season of certain species or individuals.

For convenience the breeding cycle may be described as made up of a series of terms as follows:

1. Migration to Breeding Area; 5. Incubation and Care of Eggs;
2. Courtship and Mating; 6. Care of Young in Nest;
3. Nest Building; 7. Care of Young out of Nest;
4. Laying Eggs in Nest; 8. Migration to Feeding Area.

Beginning at 2, 3 or 4, according to circumstances, the cycle may be repeated one or more times within the breeding season, or a new cycle may be begun, and stayed at any step from nest-building to laying of the eggs. Again, an entire cycle may be brought near the close, and then scamped, the young being left to die.

The reproductive cycle may be graphically represented by a number of tangent circles, each of which stands for a distinct sphere of influence or for a subordinate series of related impulses. It is evident that these serial instincts must be in relatively perfect harmony, or if regular perturbations occur, new and permanent adjustments must be forthcoming to meet them, if the species is to continue to exist. One act or series of related acts must be performed in preparation for that which follows. The nest must "anticipate" the eggs, and not the egg the nest. Upon the whole the serial instincts of birds are well attuned, yet disturbances more frequently occur than is commonly supposed, and by conditions of this kind much that is anomalous or eccentric in the behavior of birds can be explained, as we shall later see.

The cyclical instincts are profoundly affected by fear at terms 3 and 4, and the whole fabric of instinctive life is subject at nearly every step to the modifying influence of intelligence. In the reproductive cycle, as elsewhere, the same struggle is seen between competing or conflicting instincts, especially where attunement is imperfect, leading now to a fuller expression, and now to a total neglect of the usual activities. The number of terms, of which eight are given above, is unimportant, so long as it is recognized that they occur in serial form, and that many activities such as brooding, and feeding the young, are recurrent.

Certain subordinate instincts rise and wane during the reproductive cycle, thus adding to the complex of behavior. Song, which is primarily instinctive, often begins in the male during the time of mating, but that it is not wholly dependent upon the reproductive function is proved by the fact that it is not always coincident with the breeding period. Thus, it was shown as early as 1834 by Blackwall, that singing may cease before the nest is built, or last long after the young have flown. Again the fighting instinct usually emerges early (at 2 or 3) and is long continued. In that inbred pugnacity, which characterizes the breeding season of birds and higher animals, we possess the key, as I believe, to the origin of the instinct of incubation. According to this
PSM V76 D541 Female robin shielding on a hot day.png
Fig. 1. Female Robin in a partial shielding Attitude, on a hot day.
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Fig. 2. Kingbird in typical shielding Position, standing over young, with wings partly spread, and feathers partly erect.

idea the guarding evoked by the fighting instinct, and supplemented by the instinct to cover or hide the eggs, is responsible for the incubating instinct, which in the modern birds is usually strongest in the female, but is not always confined to that sex.

The possible stages in the evolution of the instinct of incubation in the reptilian ancestors of birds, upon the basis of selection, may have been as follows: first burying the eggs, like the turtle; secondly, burying or concealing the eggs and guarding them, the necessary warmth being furnished by decomposing vegetable débris, as in the alligator, and not directly from the sun; thirdly, laying the eggs and sitting over them to conceal as well as to protect them,[3] in a secluded place, the necessary heat now being furnished by the body of the parent. In the first instance the eggs may not have been concealed, but it seems probable that the instincts of both concealment and pugnacity were contemporaneous, as they were certainly very early in origin.

With incubation is associated a variety of interesting and important instinctive activities, such as rolling the eggs with the bill upon entering the nest, as may be observed in the great herring gull, placing them in position, or stirring them up with the feet, to be seen also in the gull, the domestic fowls and in a great number of wild species; covering the eggs when leaving them, a common practise of the grebes, or standing over the nest and with spread wings shielding the eggs from intense heat, as I have once observed in the least flycatcher; cleaning the nest by removal of broken or addled eggs, which must frequently occur in many species, which I was once fortunate enough to witness from the tent in the least tern on one of the Weepecket islands in Buzzard's Bay. On a very hot day in July one of the eggs, during the absence of the birds, exploded with the report of a pop-gun and blew a small hole in one side. Upon her return this resourceful bird inspected the nest for a moment, and bending down, inserted her lower mandible in the blow-hole; then lifting the heavy egg in her bill, she bore it off slowly over the water and dropped it in the sea. At her next visit every particle which might defile the nest was gathered up and carried away.

The care of the young in the nest (6) embraces a number of fairly well stereotyped, recurrent acts such as (a) the search after prey, its capture and subsequent treatment; thus some birds regularly mince the prey or beat it into a pulp, while others, like the little house wrens, bring moths and various insects to their nest with wings and legs, or with wings alone, removed. Kingbirds have been seen to bruise unruly insects between their bills while at the nest, one assisting the other, and have been photographed in the act, while it is not an unusual sight to see an insect which has been inserted in the mouth of a nestling, withdrawn, minced with the bill, and offered again. When behavior is free the return to the nest (b), is prompt and direct, but birds will frequently pause at some point near by and look about as if for assurance. The black-billed cuckoo if timid or suspicious, will sometimes stand on such a perch with insect in bill for five or ten minutes without uttering a sound, but occasionally pumping its tail, stretching its head and looking cautiously around, or again it will remain perfectly quiet like a statuette. The actual path which is now taken to the nest is eventually

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Fig. 3. Robin "taking aim." After photograph by John B. Parker.

determined by habit. The bird flies to a certain branch, grasps certain twigs, before it finally lands on a certain part of the nest itself. Then usually follows a pause as the bird straightens up and stands over her young. If the mate is brooding, as is likely to be the case in bad weather, a call-note is sometimes given by the visiting bird, when the sitter promptly retires. This note is often heard in the absence of the mate, when it serves as a stimulus to the young. Further the sitter, if a cuckoo, always detects the approach of the visiting bird by hearing, if not by sight, so that the whole family is practically never seen together at the nest, contrary to what often happens with gulls, robins, cedar-birds, kingbirds, or some of the warblers. The young detect the approach of the parent by sight or sound, or by the vibration imparted

PSM V76 D544 Robin serving one young at at time.png

Fig. 4. Robin ix Similar Phase of the Feeding Progress, but with young at later stage of nest-life. Illustrating type of direct feeding, where one bird only is commonly served at each visit. After photograph by John B. Parker.

to the nest itself or to the branches about it, and if hungry respond with the greatest vigor and excitement. When response is dull or lagging, however, the parent usually utters a call-stimulus, a peculiar note, of low pitch, and varying in quality in different species; if this should pass unheeded, it may become very shrill and rasping.

Feeding the young in birds is either (a) a passive process characteristic of certain precocious birds like gulls, in which the food is regurgitated from stomach and gullet upon the ground (Figs. 11 and 12) or (b) it is very direct, in which case the food is generally inserted into the throat (Figs. 7 and 8), the common practise of altricious birds. In the first instance, a young gull, the hatching of which was witnessed, received its first food, consisting of small lumps of predigested fish, when two hours old, and at the nest. Although this food was placed within easy reach of the chick, and was even picked up and held before its bill, no other encouragement was given and it was never inserted into mouth or throat.

The essence of the direct method of feeding is to test the swallowing reflex of the nestling. The food may be carried in gullet or stomach, and regurgitated from one or both to the mouth, before service, or it may be carried visibly in the bill, as in robins and passerine birds generally, and fed direct from bill to throat, one bird only, as a rule, being fed at each visit of the parent. Thus cedar-birds regurgitate mainly from the gullet (Figs. 5 and 6), and the berries or insects come out entire, but covered with slime, more than one bird being quickly served at each visit. In woodpeckers and goldfinches, which are fed at longer intervals, the food comes up in the form of a "pap" or "mash," probably from the stomach in part, to judge from the outlines of the neck, and all are fed rapidly as before.

The nestling gives the "opening" response, and shows its "food-target," while the parent, if a robin, vireo or one of many altrices, "aims*" (Figs. 3 and 4) and inserts the food deep into the throat, presses it gently down, and watches it, watches, we may say for the swallowing reflex of the throat. If not quickly taken, the food is whisked out and passed around, one bird after another being tried in succession, until a throat with the proper reaction-time is found. There is commonly no distribution of food among the offspring, on any other basis than this. The youngster which can react most promptly, is thus favored, because he holds up most of the food; accordingly he grows fastest, and outstrips his competing nest-mates. The young cowbird drives the children of its nurse quickly to the wall because it reacts with greater vigor from the first, and interferes with any proper distribution of the food. It is not uncommon to see the same bird, usually the larger and stronger one, fed two or three times in succession, but the full gullet checks the swallowing reflex, and thus automatically applies a brake to the greediness of a nestling, which might otherwise gorge itself to suffocation.

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Fig. 5. Cedarbird at Nest with full Gullet. First stage in reaction of young.

It must be noticed, however, that the goldfinches, referred to above, afford a partial exception to this rule. The young at the two nests of this species, which I have studied, were invariably fed with a white or greenish, sometimes frothy, semi-liquid seed-pap, each bird getting some, and at times from two to four doses, at each visit. Such birds react with great uniformity, and are remarkably uniform in their growth (Figs. 9 and 10). The feeding is extremely rapid, and so little of the pap is ever lost, that on only one or two occasions have I been able to get a drop of it for examination. It consisted of very small, immature seeds of some plant like the bull thistle or mullein.

PSM V76 D546 Cedarbird serving several young at a time.png

Fig. 6. Cedarbird beginning to Regurgitate. Final stage in reaction (opening response) of young. Feeding is by regurgitation and direct, several being fed at each visit.

While all the common passerine birds of the country feed their young in the way described, at nests of the cuckoos a most singular and remarkable performance may be witnessed, for these interesting birds not only test the throats of their clamoring brood in the usual way, but practise what may be called mouth-feeding also. Thus we have repeatedly seen the female black-billed cuckoo bring to her nest caterpillars, or larvæ of some of the larger moths, from two or three inches long, already limp, and pinched at a point just behind the head. At the food response or opening reaction, she would lay the insect in the mouth of the young one, and without relaxing her grip, hold it there, mother and child standing immovable from two to five minutes by the watch, until suddenly the machinery would begin to work, and the long body of the larva would slide down the throat of the nestling, as if greased. The insect was laid crosswise between the mandibles, which closed upon it, but not always with sufficient force to hold it, for when the parent relaxed her grip, on more than one occasion it fell on the nest, and was picked up and offered again in the same manner. During this period of suspense, the mouth of the little bird would water copiously, and now and then the insect would be moved slightly by the parent, or withdrawn and returned to the same bird.

When the feeding is over, inspection (e) follows with clock-like regularity, provided always that behavior is free, and with head inclined to be prone, the parent inspects young and nest, with a view of cleaning them (/) which means the removal of the excreta, or of any particles of food which may have escaped the young. The cleaning instinct is very wide-spread among the whole class of birds, which from the human standpoint are probably the cleanest of all vertebrates which live out of water.

The study of the cleaning instinct in birds offers many surprises, and shows us plainly that besides the question of sanitation, which might be assumed to be of paramount importance, there is the element of concealment, which in the smaller and more timid species really counts for more, while of lesser significance is the value of the excreta as food for the adult. A young bird ordinarily mutes shortly after the food taken reaches its stomach, or at least after it is swallowed, and in so doing instinctively turns so that the raised hinder end of its body is directed toward the margin of the nest. Consequently the sac, when allowed to fall, usually lands on the nest-rim, when it does not reach the ground. The excreta in cuckoos, and in most passerine birds, to mention but two prominent orders, are in the form of tenacious, mucous sacs, which are snapped up as they leave the cloaca of the nestling, and are either eaten or removed (Fig. 14). This sac resembles a rubber water bottle with thin transparent walls closed on all sides, which can be rolled or picked up without soiling bill or fingers. Digestion is very rapid in nestlings, and remains of insects have been found in a sac from a black-billed cuckoo but four hours old. But while the digestive process is rapid, it is often very imperfect, and compact fruits like the blueberry will sometimes pass the alimentary tract without change. This in part explains the use of the excreta as food, and suggests that whether they are to be eaten or removed it is only a question of hunger at the moment. Robins, when they do not devour the sacs outright, carry them away, flying low with depressed head, and drop them a few rods from the nest, but are sometimes seen to peck at them after reaching the ground. In some species, like cedar-birds, and again in certain individuals only, the excreta are more regularly and continuously eaten than in others, and there can be no doubt that habit often decides the question. Fear, however, is another variable to be reckoned with, for if this sense is aroused at the moment the bird has seized a sac to bear it from the nest, it seems to be eaten as the easiest solution of the difficulty. Perhaps a counterpart of this sort of behavior is seen when a bird with food in bill suddenly encounters the naturalist, or any other fearsome object, for it immediately sounds the alarm, and promptly swallows the insect. When more than one sac is taken, all are usually eaten. It is not an uncommon sight to see a bird walk around the nest and take a "white marble" from three birds in succession, for in muting, a bird is sometimes followed by one or more of its mates, and anything which soils the nest is quickly removed. More than once I have seen a sac, which had dropped from a nestling snapped up by the old bird before it had fallen two feet in the air; and birds will even descend to the ground for the sacs, if necessary. Twice I have seen the male chestnut-sided warbler take a sac to carry it off, and the hungry female snatch it from him, devour it and settle down to brood.

Removing the excreta piecemeal and dropping them at a safe distance is the common instinctive method not only of ensuring the sanitary condition of the nest itself, but, what is even more important, of keeping the grass and leaves below free from any sign which might betray them to an enemy. Bluebirds and redwing blackbirds often carry the sacs a long distance before letting them fall. Crow blackbirds sometimes drop them in the water, and house wrens and nuthatches implant them on the bark of trees. This instinct, like so many others in the reproductive cycle, after running its course, begins to wane, and even before the close of nest-life, so that it is not correct to say that the nest of the cuckoo or the nicker is always sweet and clean. I examined a hoopoe's nest in upper Egypt, near Luxor, on March 26, which was filthy in the extreme, but hardly worse from a sanitary standpoint than is a woodpecker's hole at a corresponding period. This nest of the hoopoe was on the ground in the midst of a pile of sun-dried brick, and was composed wholly of weeds and lentil-pods. The five young ones, which were at this time nearly ready for flight, showed their fear by erecting their beautiful crests and crawling down among the bricks to hide. There is the further curious anomaly regarding this practise, that some of our most attractive birds, which have delicate and artistic nests, of which I can mention the American goldfinch, do not appear to possess the cleaning instinct at all, or the attendant instinct of inspection, and shortly after the young emerge their surroundings become encrusted with filth. This singular fact is, I believe, correlated with the method of feeding described above. The young are fed at rather long intervals; at one period, of nearly seven hours, the average was once every twenty-five and one half minutes, and all are rapidly, and repeatedly fed at the same visit. Indeed the movements are so rapid that it is not certain that they are effective in every ease. These conditions lead to irregular muting, and to practical difficulties in regard to the sanitation of the nest, or more particularly of the nest-site. To the acts recorded above we have to add (g) incidental behavior at the nest, more or less related to care of the young, as brooding, shielding or spreading over the nestlings in heat (Figs. 1 and 2), or rain, whether sitting or erect, bristling, puffing or swelling out the throat,—possibly with air-sacs distended,—preening, gaping in hot weather, stretching and yawning, with the guarding and fighting instincts,

PSM V76 D549 Black billed cuckoo approaching nest with food.png

Fig. 7. Black-billed Cuckoo approaching Nest with Food. First stage in reaction of nestlings; wings vibrating in young which gives most vigorous response.

called into evidence as occasion may arise. Sporadic-additions are sometimes made to the nest, and I have seen the white-bellied martin return to her nest-box a feather which the wind had blown out (Fig. 13). Eagles and hawks will occasionally bring fresh sprays of hemlock or seaweed to their eyries and the great herring gull while incubating or brooding will sometimes bend over and pull fresh grass and weeds within the reach of her bill, and tuck them under her body. Most of these acts are probably instinctive in origin, but they are far from predictable.

It would be safe to affirm that the cuckoo or the cedarbird which we happened to be watching, would in the course of time come to a certain branch, look about, advance to the nest along a certain path, marked out previously by habit, test the throat of one of the eager young, watch for the swallowing reaction, inspect and take the sac, if forthcoming, in the bill, but here no one could say whether the sac would be borne away, and the bird return thereafter with food, or whether it would be eaten, and the bird remain at the nest to brood. Here association and other elements seem to enter. My records for the cuckoo show that the brooding intervals, as to their length and frequency,

PSM V76 D550 Cuckoo feeding young serving one bird at a time.png

Fig. 8. Cuckoo placing Food in Throat ("testing" the throat); wings of nestling at rest. One bird only receives food.

seem to depend upon the intensity of the light and the activity of the male. During the early period of nest-life many birds brood through the night, but at intervals only during the day. When the sun becomes suddenly obscured with dense clouds, or it grows dark with the approach of rain, brooding is likely to begin, and if the male ceases to bring food, the brooding intervals are prolonged. Thus, during a heavy rain storm I have known the black-billed cuckoo to brood for the space of one hour and forty minutes, and only retire at last at the approach of her mate with food. After his task was accomplished, the female returned with an insect, and resumed her brooding again.

The instincts of the parent and young are of the lock and key order. Each acts as a stimulus to the other, and the reward of satisfaction to the child is no greater than that of pleasure to the parent. The coordinated instinctive responses of the young begin in many of the precocious birds, like the great herring gull, before birth. The egg is starred and pipped, and the bill of the little bird is seen, and its call note heard, for several hours before the shell is cracked open. The

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Fig. 9. Goldfinch feeding Seed-pap by Regurgitation. Note uniformity of response.
split may occur with a certain degree of uniformity in the direction of the minor axis of the egg, thus dividing it into two equal or unequal parts, and when the chick crawls out it leaves, besides the shell and its membrane, the allantois, and what looks like a residue of the albumen. The shells which now encumber the nest are carefully removed by some birds, and dropped, presumably at some distance away, while in others they are brushed aside, or crushed by the brooding bird and receive no further attention. This removal of the shells so common in the Passeres and other orders, must be attributed to the cleaning instinct, and I have noticed that in the cuckoo, which removes the shells of the first two or three young to hatch in succession, is apt to leave those of the last when the cleaning instinct is on the wane. The allantois is sometimes picked out of the shell and eaten, as has been seen in the case of the gull.

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Fig. 10. Goldfinches Pyramid of Five Young and One Adult at later Stage in Nest-life. Type of direct feeding by regurgitation, where all birds are served at each visit, and some more than once. Note uniformity in response and in size of the nestlings.

The initial instincts of the young depend upon the degree of development attained at birth, and are manifested in every phase from a precocious bird like the snipe, which is horn seeing and with a full coat of down, to the altricious cedar wax wing, which is stark naked, and is blind up to the second or fifth day. The precox emerges with feathers wet with the amniotic fluid, and remains at the nest at least long enough to dry off, while the more slowly maturing hawk or eaglet, though down-clad and alert from the first, is tended for weeks or months at the nest. MacPherson, who has described the home life of the golden eagle, which he carefully watched on a cliff in the highlands of Scotland, found that the young were fed at the eyrie eleven weeks before they were ready for independent flight.

The initial responses of the altrix, of which the cedarbird, and, with some qualification, the cuckoo, may be taken as a type, to be seen at birth or shortly after, are (a) the power of orientation, (b) the grasping reflex of the feet, (c) the food-response, (d) the call note, and (e) the characteristic actions in muting, following feeding, as a result of the stimulus of food, and possibly of the attitude of inspection assumed by the adult. Later follow other specific call and alarm-notes, pecking, gaping, stretching, spreading in response to heat, preening, bristling and certain attitudes expressive of fear, flapping and flight. After leaving the nest, we observe the more perfect performance of activities already begun within it, as pecking, crouching, standing erect with head upturned so admirably illustrated in the cuckoo, and especially in the cedar waxwing, where its use for concealment is obvious, as well as following, hiding, play, imitation, preying, and the more perfect expression of flight, finally followed by migration in late summer or fall, which may be performed, as in the cuckoos, quite independent of the parents.



The description of the reproductive cycle given above is a composite, and applies most completely to the altricious birds, which are born blind and would quickly perish but for timely care of their parents. There are many special instincts in the twelve thousand or more species of known birds, but few of which have been adequately studied, and there are many minor variations in every term of the series, the discussion of which would require a volume.

The power of the parental instincts to banish fear in all classes of the higher animals has been recognized and admired from antiquity, and nowhere is this more clearly seen than in the brooding bird. The ancient Israelites were forbidden to take the mother bird with her young, because at certain times, as one commentator has observed, she will not avail herself of her power of concealment and flight, the object

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Fig. 11. Great Herring Gulls on Preserve; chicks on feeding spot, watching old bird, and following her movements.

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Fig. 12. Gull Regurgitating, and the young seizing the shrimp, squid, or fish as they leave the mouth or fall to the ground. Type of indirect feeding by regurgitation.

of the law being not merely to preserve the game, but to signalize the sanctity of this instinct.

The brooding instinct rises like a fever, reaches a culmination at the time the eggs hatch or shortly after, and then rapidly subsides. At the same time there is a corresponding depression of fear, which returns with the waning of the brooding impulse. Thereafter brooding becomes more intermittent, being determined in some degree by the intensity of light, and weather conditions, with the difference that fear is now in the ascendent, and the element of intelligence, at the plane of association at least, is not lacking. At its first manifestation it affords a beautiful illustration of a pure instinct, adapted to the preservation of the offspring, though attended at times by what blind and costly sacrifice of life can well be imagined.

At the command of the brooding instinct, or at the sight or touch of the eggs, and later of the young, the whole nature of the bird is quickly changed. In his experiments with noddy and sooty terns, Watson[4] found that while neither bird recognized its own egg, the habits of a laying noddy could be almost immediately changed into those of a "sitter" by placing an egg in its nest. Before the appearance of the egg, this bird is shy and easily disturbed, but contact with an egg, and an artificial one at that, seemed to change its disposition at once, for it would then stay by its nest and strike angrily at an intruder. The reverse of such behavior was further seen when the egg of a "sitter" even after several days of incubation, was summarily removed.

The cedarbird, ordinarily so timid that it will promptly abandon its new made nest if disturbed in the slightest degree, in the course of a few days becomes so "bold" as to submit to any change which the experimenter chooses to make. I have known this bird to stand on its displaced nesting bough, which had been sawn from a tree and mounted on stakes in a field for close-at-hand study, to permit the writer and a companion to approach within three feet and inspect bird and nest at leisure, while the adult assumed that curious bold upright attitude, with beak pointed to the zenith, in which nature seems to transform the actor into a part of the tree itself.

In my work on "The Home Life of Wild Birds" numerous illustrations of the action of this remarkable instinct are given. In one case a flicker, before so wary, for a few days after the young were born, would permit of any liberties, even to the sawing of a large window in the side of her nesting tree, without budging a feather, not even to shake the sawdust from her back, and allowing herself to be enclosed in the hand. In the Bahama Islands I have taken both the yellow-billed

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Fig. 13. White-bellied Martin returning a feather to her nest, from which it had been blown by the wind the moment her nest-box was opened.

tropic bird and the sooty terns from their nests, but was careful in the case of the former to avoid the thrusts of their sharp, stiletto like bills.

To keep within the more familiar species, and nearer at home, on July 18, while fishing a trout-stream, I passed two robin nests in apple trees, each with three eggs, more or less incubated. Note the difference in behavior on the part of their occupants, doubtless due in part to difference in individuality. In passing within a few yards of nest No. 1, the sitter immediately flew out in a great state of excitement, and shot off her characteristic emphatic alarms. At nest No. 2 I could

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Fig. 14. Nest-cleaning in the House-wren, which has the practise of removing the sacs and implanting them on the bark of trees.

see the tail of the sitter projecting over the edge of the nest, as I walked under her tree. This was poked with the fishing rod, but with no response. Then I separated her tail-feathers with the tip of the rod, and poked harder. At this the old robin faced about and pecked angrily at the rod, and snapped her bill with the address of a flycatcher. Then I ruffled her already erect crest and back-feathers, only to receive more thrusts and snapping from the bill, and it was only after the roughest kind of treatment that this bird was finally dislodged, so that I could examine her nest.

To give a final illustration of the working of this instinct, on July 19, at eleven o'clock, I discovered a black-billed cuckoo in the act of brooding one young bird, a day old, and three eggs, in a small sapling pine, about three feet from the ground. The sitter, thus surprised, quietly retired and sounded her alarm from a distance. Twenty-four hours later, when I visited the scene, and when, as afterwards appeared, a second young bird had emerged, fear was more in abeyance, and the behavior different. I was allowed to approach as close as possible, and stood for twenty minutes, with the eye of the sitter not over twenty inches from my own, and only finally sent her off by trying to take her in the hand. Under these circumstances the cuckoo behaves much like the cedarbird, raising its head, though in a less marked degree, and remaining perfectly quiet, the only motions visible being those of breathing and the momentary flick of the third eyelid or nictitating membrane across the pupil.


The dawn of avian intelligence in the nestling, if one of the altrices, begins at about the third day, and in relation to the feeding reaction. Resting upon its huge pot-belly, as a central pillar, the little bird raises its trembling head, rather feebly at first, and supporting itself also, it may be, with its wings, and opening its mouth to the widest extent, thus displays its food-target. If the sign is unanswered, the head drops, the mouth closes, vibration ceases, and the bird lies prone, as if exhausted, the whole operation, which seems to call into play the entire body, lasting three seconds, more or less, according to the strength of the original stimulus.

This kind of behavior is a typical illustration of compound reflex action or instinct, and, when feeding follows, the reflexes assume more completely the chain form. When not due to hunger this response may be evoked at will by any suitable stimulus, whether tactile or auditory, whether the bird is in its nest or out of it, and regardless of the parent. The nestling now reminds one of an electrical toy, the action of which is purely automatic. Place the little bird on a piece of cloth or fold of your clothing and "press the button," that is scratch the cloth with the finger or a lead pencil, and behold this complex feeding response. When the nestling has not been fed to repletion, within the limits of fatigue, this reaction may be as automatic, uniform or stereotyped, and therefore predictable, as that of an electric bell.

Initial responses of this sort are relatively perfect. Consequently they can have nothing to do with past experience. They represent the hereditary powers of a hereditary mechanism. Now the point of greatest interest is that this inherited tendency to respond, in the course of a few days becomes replaced, as it were, by an acquired tendency. Instinct becomes "modified" by association. The mind or intelligence begins to take the reins, though feebly at first, into its own hands. Out of many experiments made upon the young of our common wild birds I select by way of illustration the brown thrush and black-billed cuckoo. In July 24, a nest of this thrush which I had been watching contained three birds, the youngest of which barely had its eyes open, and was from twenty to thirty hours old. When taken from its nest, at 3:15 p.m., and tested in the way suggested above, I obtained one hundred food reactions in thirteen minutes, each representing the entire complex of movements already analyzed, and each lasting from three to fifteen seconds, according to the strength of the stimulus received. A test immediately following gave fifteen reactions to the minute. The reaction time, which was very rapid at first, seemed to slow down only as a result of fatigue, but there was not a single failure to react upon the given stimulus. The same reaction was produced by clapping the hands, touching the bird, or holding its head between the fingers. On this day the two older birds, which were from two to three days old, would react while in the nest, but not when out of it. Now, upon the next day, about twenty-four hours later, as well as upon subsequent days, when the same tests were made with the same birds none of them would react when removed from the nest, with the exception that one feeble response was obtained from thrush No. 3, on July 25.

The same result was obtained with cuckoos. I was unable to get a single food-response from a black-bill, four or five days old, during the twelve hours or more that it was held a captive away from its nest. It would have starved rather than open its mouth of its own accord, and it even regurgitated the food which was pressed into its throat and gullet. Its whole conduct showed conclusively that the sense of fear had not yet appeared, but the moment this hungry bird was returned to its nest, and its feet touched the familiar twigs, it seemed to expand, as by magic, into a new creature, for standing erect, with every feather tube raised, and with vibrating wings, the neck trembling like a tuning fork, it opened its mouth and gave the food-reaction with all the vigor of which it was capable, and gave it repeatedly, loudly calling.

Edinger speaks of the modification of behavior described above, as an acquired habit, by which nestlings assure themselves against impending danger, and compares their attitude with that of an old bird coming hesitatingly to the nest, and looking about as if in anticipation of trouble. A simple experiment, however, like that just given upon the cuckoo, shows that this modification has nothing to do with assurance, for it begins long before there is any decided evidence of fear, and the little bird does not begin to look about in a suspicious manner until it is six or seven days old, when fear is arising. Moreover, all the attitudes, expressive of this instinct, both in young and adult, must, I believe, be considered as instinctive and not acquired.

What association seems to do for the young bird in the first instance is to eliminate a lot of useless reactions, by limiting its responses to those which count, for the amount of energy which goes to waste in this direction, especially up to the time of the later manifestations of fear, near the close of nest-life, must be very great. The pleasure of getting the food seems to lead to an association with the nest itself, the place where the food is received, and with the parent, the active agent, together with her calls and the vibrations of the nest or branches which attend her visits. Association with the nest seems to be strongest, for nestlings up to a late period respond freely to the call-notes of other birds, which happen to pass near, to sudden gusts of wind, at an early period especially, and to violent sounds of every description, like the distant whistle of a locomotive. A more curious sight, which illustrates the indefinite character of this association, is often witnessed up to the very last days of nest-life in many, if not all, of the common altricious birds of the country. Not only does the casual excitement of one bird arouse all the others into action, when, as it were, "the pot begins to boil," and then subsides, but the nestlings often respond to one of their mates, precisely as to the parent, for which it is plainly mistaken, crowding eagerly around it begging to be fed, and in their vain attempts to nestle under it, almost pitching it out of the nest.

In early nest-life, any sudden jarring of the nest or the branches about it will elicit the food-response as readily as when the vibration is imparted by the touch of the parental foot, but discrimination comes in this direction also, at any rate in certain species or individuals, and is often well-nigh perfect at the advent of the instinct of fear.


The acquired habits or tendencies which have been described may in time become very uniform and more or less "stereotyped," but they are widely different from those instinctive characters which alone are inherited.

We have been obliged to speak frequently of fear, which in its origin must be regarded as an instinct in birds. It should not be forgotten, however, that if very young animals of any kind are separated from their parents, so that their natural environments and experiences are changed, we may look for a modification of this instinct, both as to the degree and manner of its expression, and as to the time of its appearance. In all the common altricious birds fear, in its later stages, is attuned with the instinct of flight, or, as in the case of the cuckoo, with the power of helping itself by entry upon a climbing stage, when seven days old. In a cedar waxwing, on the contrary, it is not well matured until the thirteenth or fourteenth day, when the entire brood, standing on their nests with heads upturned, suggest a gun, loaded, capped and primed, ready to go off as soon as some one pulls the trigger, which is of the hair variety. When this instinct is ripe, the plucking of a single leaf, or any unusual sight or sound will send all off in a panic. They scatter in every direction, making flights both long and good for a first effort, or, if less mature, down they all go flapping to the ground and, if robbins, squealing their danger-signals in high-pitched voices, indicative of that fear which shows in every attitude and note. Correlation, however, is not always perfect, and in consequence of the prematurity of fear many young birds flutter out of their nests in a helpless condition, to meet certain destruction from their numberless enemies on the ground.

That fear in birds may be connate, or present at the time of birth, seems to be clearly implied by an interesting experience reported by Hudson.[5] He was fortunate in finding a nest of the La Plata jacana (Parra jacana) on a small mound of earth in a shallow lagoon, with four eggs the shells of which were already chipped. Dismounting from his horse, he picked up one of the eggs and held it for a moment in the palm of his hand, when, as he says:

All at once the cracked shell parted, and at the same moment the young bird leaped from my hand and fell into the water. I am quite sure that the young bird's sudden escape from the shell and my hand was the result of a violent effort on its part to free itself; and it was doubtless inspired to make the effort by the loud screaming of the parent birds, which it heard while in the shell. Stooping to pick it up to save it from perishing, I soon saw that my assistance was not required, for immediately upon dropping into the water, it put out its neck, and with the body nearly submerged, like a wounded duck trying to escape observation, it swam rapidly to the second small mound I have mentioned, and escaping from the water, concealed itself in the grass, lying close and perfectly motionless like a young plover.

In this remarkable case the whole complex of behavior is as plainly expressive of fear at every step, as it is evidently the free gift of heredity.

  1. Eimer, Theodor G. H., "Organic Evolution," p. 256, London, 1890.
  2. Edinger, Ludwig, "The Relations of Comparative Anatomy to Comparative Psychology" (translated by H. W. Rand), Journ. of Comp. Neurology and Psychology, Vol. XVIII., No. 5, 1908.
  3. It is evident that pythons, which lie upon their eggs, secure in this way both protection and concealment for their offspring.
  4. Watson, John B., "The Behavior of Noddy and Sooty Terns," Pub. No. 103, Carnegie Institution of Washington, p. 223, Washington, 1909.
  5. Hudson, W. H., "The Naturalist in La Plata," pp. 111-112, London, 1892.