The complex architecture of avian nest defense: Between paralyzing instinct and adaptive intelligence

“ In the building of the nest, the family safeguard, we see the highest manifestation of the faculties of instinct. That clever architect, the bird, teaches us as much; and the insect, with its still more diverse talents, repeats the lesson, telling us that maternity is the supreme inspirer of instinct. Entrusted with the preservation of the species, which is of more importance than the preservation of individuals, maternity awakens in the drowsiest intelligence marvellous gleams of foresight ”

“ The blithest bird upon the bush
⁠Had ne'er a lighter heart than she.
But hawks will rob the tender joys
⁠That bless the little lintwhite's nest;
And frost will blight the fairest flowers,
⁠And love will break the soundest rest. ”

“ The wisdom of birds in the selection of nesting sites, the designing of the best nest for their respective wants, and finally the construction of them, indicate instinct, reasoning power and mechanical skill of a high order. The range from the wonderful woven homes of the weaver bird and the Baltimore oriole down to the bare and nestless incubating spot of the penguin is so great that nothing less than a volume can furnish space in which to set it forth. But let us at least take a brief glance at a wide range of home-building activities by birds. ”

“ By short jerks they usually caught the winged insects. Sometimes they ascended into the air and dropped like an arrow; at other times they hovered like a hawk when set on its prey. They drove off most vigorously all kinds of small birds that approached their nest, as if bidding them to go and hunt in their own grounds, where there were plenty of flies for them. Sometimes they brought only one fly in their bills, sometimes several, and flies of various sizes. ”

“ Why, on the contrary, in critical, decisive moments, when danger confronts them, when their existence is threatened, when nothing is more imperative than flight, attack or defence, do we see animals paralysed with trembling, incapable of struggling, and perishing without their strength having in the least profited them? ”

“ Weakness produces fear, and fear produces weakness. Here is a fatal revolution in the functions of the organism. Of what use are the arbitrary and imaginary distinctions philosophers have made in the functions of the mind, when they cannot be separated from those of the body? There are in life fatal cliffs, currents which we cannot stem, and which carry us to inevitable destruction.
Weakness increases excitability, excitability foments lasciviousness, and lasciviousness in its turn begets weakness. ”

“ What we call instinct is the voice of past generations reverberating like a distant echo in the cells of the nervous system. We feel the breath, the advice, the experience of all men, from those who lived on acorns and struggled with the wild beasts, dying naked in the forests, down to the virtue and toil of our father, to the fear and love of our mother. ”

“ On the other hand, the associations of the processes can not be broken, and the skill which the bird directs to building her nest is not capable of being employed for any other end.
The more developed the instinct, the more stable are the combinations of phenomena and nervous conditions under which it works; the weaker the combinations, the more nearly the animal's mode of action approaches what we call reason. ”

“ If approached gently, in the absence of their parents, callow wild birds in their nest exhibit little alarm at the slow and gentle approach of man. Mr. Hudson’s opinion has already been quoted, but will bear repetition; it is, “that fear of particular enemies is in nearly all cases the result of experience.” And there is no evidence to show that, in those cases in which it is truly instinctive and not the result of experience, the instinctive behaviour is necessarily due to inherited habit and not to natural selection. ”

“ Anything unfamiliar,—darkness, a state of exhaustion, weakness, fatigue, arouses the fear instinct, startling the animal into running, hiding, crouching, and preparation for attack or defense.
The fear instinct stays with us, and watches over us day and night. It follows us closely in our active, waking life, attends us in our resting hours, and watches over us in our sleeping periods. The fear instinct is the last to fall asleep, and the first to awake. ”

“ When one considers as a whole the symptoms by which fear reveals itself, one might almost think that it was a product of heredity and selection. Animals that are easily frightened, a disciple of Darwin would say, are those which can more easily avoid danger and save themselves; these produce young, and perpetuate their timidity in their posterity. ”

“ Our machine is so made that it changes automatically as required, without the interference of the will being necessary. The palpitation of the heart from fear is the exaggeration of a fact which we always notice, whenever the organism must develop its maximum of energy and increase the circulation in the nerve-centres; the heart does not work for itself, but for the brain and muscles, which are the instruments of combat, attack, defence, and flight.
The greater or lesser frequency and force of the pulse in emotion depends upon the greater or lesser excitability of the nerve-centres. ”

“ Certainly an animal that does not move can more easily escape from an enemy. Darwin remarks that when an animal is alarmed, it stops an instant to collect its senses and discover the source of the danger, and decide whether it should escape or defend itself; but this is certainly not the origin and reason of the phenomena of cataplexy and fear, which we must consider as a serious imperfection in the animal organism. ”

“ Where horror includes fear, it is fear mingled with abhorrence. (See ABHOR.) Affright, fright, and terror are always sudden, and in actual presence of that which is terrible. Fear may overwhelm, or may nerve one to desperate defense; fright and terror render one incapable of defense; fear may be controlled by force of [169] will; fright and terror overwhelm the will; terror paralyzes, fright may cause one to fly, to scream, or to swoon. Fright is largely a matter of the nerves; fear of the intellect and the imagination; terror of all the faculties, bodily and mental. ”

“ But this is not correct, these also are cataplectic phenomena. When defenceless birds see a serpent approach their nest, they begin to scream and flap their wings, as though trying to draw its attention upon themselves, and so to save their young. Blinded by love and emotion they rush upon the enemy and then remain as though paralysed, scarcely moving wings or claws, or else they let themselves fall into the jaws of the serpent and are devoured. ”

“ Fear is more manifest in birds than in any other animal. We sometimes see jugglers, as a proof of their magic power, take a little bird in their hand and lay it on its back, showing that it no longer moves, although it might easily fly away. ”

“ Some animals and many insects remain for a long time motionless when danger threatens. To one of these zoologists have given the name of anobium, as though it feigned death when touched. Many other coleoptera act in the same way, not even moving when they are caught, transfixed with a pin, and roasted over a flame. Preyer justly remarks that this cannot be a feint, nor an instinct which tells them to preserve the appearance of death as a means of saving their life; for it would then be incomprehensible that they should let themselves be burnt alive rather than abandon the deception. ”

“ The paralysis which comes of fear can be lifted only through the resumption of action which will again give individuals the feeling of organization. This does not mean ordering a bayonet charge, or the firing of a volley at such-and-such o'clock. It may mean only patting one man on the back, "talking it up" to a couple of others, sending someone out to find a flank, or turning one's self to dig-in, while passing the word to others to do likewise. ”

“ That birds can go beyond mere imitation, and are to some extent accomplished actors, the evidence as to all those birds which, by false pretences of agitation, lure the trapper away from the vicinity of their nest, completely shows. ”

“ But in proportion as the bird makes so insufficient and unguarded a nest, so all the greater is the anxiety, both of herself and her mate, about the eggs. Hence, whilst she is sitting, he exercises all kinds of little arts to entice away every intruder from the nest, wheeling round and round in the air near him, so as to fix his attention, screaming mournfully his incessant peewit till he has drawn him ever further and further from the point of his anxiety and love. ”

“ How different are these collecting movements to those which we see in a bird whose nest-building instinct has become more highly developed! They seem to be but just emerging from the region of blind forces, to be only half purposive, not yet fully guided by a distinct idea of doing something for some definite end. Yet it is just these actions which most resemble ones which seem so purposive in the ordinary building of a nest. ”

“ The instincts of even the higher animals are often followed in a senseless or purposeless manner: the weaver-bird will perseveringly wind threads through the bars of its cage, as if building a nest: a squirrel will pat nuts on a wooden floor, as if he had just buried them in the ground: a beaver will cut up logs of wood and drag them about, though there is no water to dam up ”

“ Audubon has given several remarkable cases of differences in nests of the same species in the northern and southern United States. Fear of any particular enemy is certainly an instinctive quality, as may be seen in nestling birds, though it is strengthened by experience, and by the sight of fear of the same enemy in other animals. But fear of man is slowly acquired, as I have elsewhere shown, by various animals inhabiting desert islands ”

“ Other fledglings simply shrink down in the nest or squat close on the ground, their fear, apparently, being in proportion to the suddenness with which the strange animal or object comes on them; but, if the deadliest enemy approaches with slow caution, as snakes do--and snakes must be very ancient enemies to birds--there is no fear or suspicion shown, even when the enemy is in full view and about to strike. ”

“ Another proof that the nestling has absolutely no instinctive knowledge of particular enemies, but is taught to fear them by the parents, is to be found in the striking contrast between the habits of parasitical and genuine young in the nest, and after they have left it, while still unable to find their own food. ”

“ 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. ”

“ The building of nest on nest, or of new nest on the site of the old, according to this interpretation, gives rise to the wonderful storied structures sometimes produced by the yellow warbler, or vireo, when plagued by the cowbird. That the intruding egg is buried out of sight is not due, however, to a feat of reason on the part of the suffering bird, but is the curious result of a nearly pure instinct, modified only by association. Fear breaks the cycle, but it is not always strong enough to break the habit of going to the old site. ”

“ Whether the new nest is built upon the remains of the old, or close beside it, or half a mile away, must be attributed to the ordinary workings of instinct, modified by association and fear, when for some cause the normal cycle has been disturbed. ”

“ In acquiring the habit of building in chimneys, which has been carried to swallows by the westward course of civilization, they exhibit some faculty of adaptation. As a rule they place their nest five or six feet below the top of the chimney, to keep it out of the way of owls, not directly over the kitchen-fire, but over an adjoining flue. And it requires some art to get down into the shaft. The emergence of the young swallows from this place is a remarkable instance of intelligent action still wavering on the brink of mere hardened instinct. ”