The age of a bird is difficult to determine. Experience leads me to believe that some of the males that arrive before the females are birds born the previous season; one finds, for instance, individuals with plumage of a duller hue, which denotes immaturity, amongst the first batch of arrivals. But though plumage may sometimes be a satisfactory guide, yet to rely upon it alone, or upon a more perfect development of feather, is to exceed the limits of safety. How, then, can we ascertain whether all the males that arrive before the females have had some previous experience of reproduction? Well, we take a particular locality and note the migrants that visit it year after year, and we find that the respective numbers of the different species are subject to wide annual fluctuations. Not every species lends itself to an inquiry of this kind: some are always plentiful and fluctuation is consequently difficult to discern; others are scarce and variation is easily determined. Those which are of local distribution but conspicuous by their plumage, or easily traced by the beauty or the peculiarity of their song, afford the more suitable subjects for investigation. For example, the Grasshopper-Warbler, Marsh-Warbler, Nightingale, Corncrake, Red-backed Shrike, or Whinchat have each some distinctive peculiarity which makes them conspicuous, and each one is subject to marked fluctuation in numbers. The small plantation or wooded bank may hold a Nightingale one year, but we miss its song there the next; the osier bed or gorse-covered common which vibrates with the trill of the Grasshopper-Warbler one April is deserted the following season; the plantation which is occupied by a host of common migrants this summer may be enlivened next year by the song of the rarer Marsh-Warbler also; and so on. The fluctuation is considerable: we observe desertion on the one hand, appropriation on the other, and yet males appear before females whether the particular plantation, osier bed, or swamp had been inhabited or not the previous season. This fact is not without significance. It shows that similar conditions prevail both amongst the males that appropriate breeding grounds new to them, and amongst those that return to some well-established haunt; and on the assumption that the earlier arrivals are experienced males, the same birds evidently do not return to the same place year after year. Granting, then, that the males which appropriate new breeding-grounds are young birds, how can their earlier arrival be explained in terms of past experience; and granting that they are old, and therefore experienced, how can it be explained in terms of association?
Again, it may be urged that if there is some biological end to be furthered by this hurried return, and if recollection of past experience is a means towards that end, such recollection need not necessarily be associated with a definite place, but only in a vague way with the whole series of events leading up to reproduction—in which series the migratory journey may even have acquired meaning. Whether there be any recollection of a previous journey or of a nest with young, I do not know. But the young bird is capable of performing its journey, of building its nest, and of rearing its young antecedent to experience—racial preparation has fitted it thus far; why then exclude the other event in the series, the earlier departure of the male, from hereditary equipment? If the journey were a casual affair without any goal attaching to it, if the males upon arrival wandered about in search of a mate, there would be some ground for thinking that a vague recollection of the whole former experience was sufficient to explain the hurried return; but since the pleasurable effect of association, founded upon previous experience of a definite place, cannot well be established, and since it is so difficult to study the objective aspect of the behaviour in question without coming to the conclusion that the journey is related to the appropriation of a place suitable for the rearing of offspring, one is tempted to ask whether the hurried return may not also be so related.
Now the males of some of the migratory species, especially of those which are accustomed to return to their breeding haunts early in the season, are called upon to face greater dangers and have a greater strain imposed upon their strength by starting forth upon their journey ten days or a fortnight before their prospective mates. The blizzards which so often sweep across the northern parts of Europe in the latter half of March, destroying in their course the all too scanty supply of insect life, may take toll of their numbers; or the westerly gales, which are not infrequent at that period, may meet them in mid-ocean and add to the perils of their journey; or the temperature of the previous weeks may have been sufficiently low to arrest the development of insect life—and yet males are annually exposed to these risks in hurrying to their breeding grounds. For what purpose? The answer will largely depend upon the way in which we regard those few acres wherein a resting place is ultimately found. For myself, I believe that they are of importance, inasmuch as the securing of a place suitable for the rearing of offspring is a primary condition of success in the attainment of reproduction; and if this be so, it is evident that the interests of the race will be better served by the males making good this first step before the females are ready to pair, otherwise they might oscillate between two modes of behaviour, created by the premature functioning of conflicting impulses.
The different steps in the process seem to follow one another in ordered sequence. The male inherits a disposition—which for us, of course, has prospective meaning—to seek the appropriate breeding ground and there to establish itself; and as early a functioning of this disposition as possible, consonant with the conditions of existence in the external environment, may have been evolved for the following reasons—firstly, the earlier individuals will meet with less interference wherever they may settle, every locality will be open to them, every acre free, their only need being that particular environment for which racial preparation has fitted them. In the second place, being already established when other males appear upon the scene, and advertising their presence by song, they will be less liable to molestation; thirdly, in those cases in which a long journey is undertaken, they will have ample time to recover from the fatigue, and, if attacked by later arrivals, will thus be in a better position to defend their territories; and lastly, a greater uniformity in their distribution will be insured before the females begin their search.
There is, besides, another good reason for thinking that the earlier males will have an advantage. We will assume—and from the abundant evidence supplied by the marking of birds, it is quite a reasonable assumption—that there is a tendency, generally speaking, for individuals to return to the neighbourhood of their birthplace, or to the place in which they had previously reared their offspring. Now the earlier arrivals will have no difficulty in securing territories; those that come later may have to search more diligently, still they will gain all that they require so long as any available space remains. Then comes the point when all suitable ground is occupied, and yet there are males to be provided for. What will be the position of these males? Urged by their inherited nature, they will leave the district and possibly continue their search into those adjoining, only, however, to add to the difficulties of the males there similarly situated; and even allowing that they are at length successful in establishing themselves, what are their prospects of securing mates? Since the earlier females will not extend their wanderings farther than is absolutely necessary, but will pair whenever the opportunity for doing so arises, it is to the later females, forced onwards by competition, that the late males must look for mates; so that when at length pairing does take place, much valuable time will have been lost.
The disadvantages which the late arrivals have to face are therefore great, and it is probable that the percentage which attain to reproduction will on the average be somewhat lower than the percentage in the case of the earlier arrivals. The district in which my observations have been made lies well within the limits of the breeding range of most of our common species, and it is not surprising that I should have met with little evidence of failure to breed as a result of failure to secure territory. Some interesting information was supplied to me, however, by the late Robert Service. He found, in certain seasons in Dumfriesshire, flocks of from ten to fifty unmated Sedge-Warblers, which, from the time of their arrival in May until the middle of July, haunted reed-filled spaces along stagnant streams. These flocks appeared to him to be composed of loosely-attached individuals of a migrant flock that had failed to find things congenial enough to entice them to disperse. But may they not have been composed of males that had failed to secure territories, or of females that had failed to discover males in possession of territories, or of both?
We have seen that, in the case of many species, each male establishes itself in a particular place at the commencement of the breeding season, even though this may mean a partial or perhaps a complete severance from former companions. We must now discuss this fact in greater detail because it is opposed to the views often held regarding the sexual behaviour of birds, and is manifestly of importance when considering the theory of breeding territory.
First, however, there is a point which requires some explanation. I speak of the same male being in the same place. How can I prove its identity? In the first place it is highly improbable that a bird which roams about within the same small area of ground, makes regular use of a certain tree and a certain branch of that tree, and observes a similar routine day after day, can be other than the same individual. But, apart from this general consideration, are there any means by which individuals of the same species can be identified? Well, there is variation in the plumage. Supposing we take a dozen cock Chaffinches and examine them carefully, we shall find slight differences in pattern and in colour—more grey here or a duller red there, as the case may be—and though these differences may not be sufficient to enable us to pick out a bird at a distance, they are nevertheless conspicuous when it is close at hand. Then again there is variation in the song; and the more highly developed the vocal powers the greater scope there is for variation. But even the phrases of a simple song can be split up and recombined in different ways. If one were asked casually whether the different phrases of the Reed-Bunting's song always followed one another in the same sequence, the answer would probably be that they certainly did so, whereas the bird is capable of combining the few notes it possesses in a surprising number of different ways. And lastly, there are differences in just the particular way in which specific behaviour, founded upon a congenital basis, is adapted by each individual to its own special environment. Racial preparation determines behaviour as a whole, but the individual is allowed some latitude in the execution of details which are in themselves of small moment—the selection of a particular tree as a headquarters and a particular branch upon that tree, the direction of the distant excursion, and the direction of the limited wanderings within the small area surrounding the headquarters which in the course of time determine the extent of the territory, are matters for each individual to decide when the occasion for doing so arises. Moreover instances of abnormal coloration or abnormal song are not rare, and they are valuable since they place the identity of the individual beyond dispute. I can recall the case of a Willow-Warbler whose song was unlike that of its own or any other species, and of a Redbreast whose voice puzzled me not a little. I can recollect also a male Yellow Bunting whose foot was injured or deformed. Of this bird's behaviour I kept a record for two months or so; and inasmuch as it inhabited a roadside hedge, and was of fearless disposition, the deformed foot could plainly be seen whenever it settled upon the road to search for food. Identification is not, therefore, a difficulty. There is always some small difference in colour or in song, or some well-defined routine which makes recognition possible.
Owing to their great powers of locomotion, birds have generally been regarded as wanderers more or less; anything in the nature of a fixed abode, apart from the actual nest, having been accounted foreign to their mode of life; and even the locality immediately surrounding the nest has not been apprehended as possessing any meaning for the owner of that nest. No doubt the supply of food determines their movements for a considerable part of the year; they seek it where they can find it, here to-day, there to-morrow—in fact few species fail to move their quarters at one season or another, so that there is much truth in the notion that birds are wanderers. Yet to suppose that every individual one sees or hears—every Lapwing on the meadow, or Nightingale in the withy bed—is in that particular spot just because it happens to alight there as it roams from place to place, is to take a view which the observed facts do not support. For as soon as the question of reproduction dominates the situation, a new condition arises, and the habits formed during the previous months are reversed, and the males, avoiding one another, or even becoming actively hostile, prefer a life of seclusion to their former gregariousness—all of which occurs just at the moment when we might reasonably expect them to exhibit an increased liveliness and restlessness as a result of their endeavour to secure mates; and so universal is the change that it might almost be described as an accompaniment of the sexual life of birds generally.
That the Raven and certain birds of prey exert an influence over the particular area which they inhabit has long been known, and it has been recognised more especially in the case of the Peregrine Falcon, possibly because the bird lives in a wild and attractive country, and, forcing itself under the notice of naturalists, has thus had a larger share of attention devoted to its habits. Moreover, when a species is represented by comparatively few individuals, and each pair occupies a comparatively large tract of country, it is a simple matter to trace the movements and analyse the behaviour of the birds. There is a rocky headland in the north-west of Co. Donegal comprising some seven miles or so of cliffs, where three pairs of Falcons and two pairs of Ravens have nested for many years. Each year the different pairs have been more or less successful in rearing their young; each year the young can be seen accompanying their parents up to the time when the sexual instinct arises; and yet the actual number of pairs is on the whole remarkably constant, and there is no perceptible increase. It seems as if the numbers of three and two respectively were the maximum the headland could maintain. But this is no exceptional case; it represents fairly the conditions which obtain as a rule amongst those species, granting, of course, a certain amount of variation in the size of each territory determined by the exigencies of diverse circumstances.
If we take a given district, and devote our attention to the smaller migrants that visit Western Europe each returning spring for the purpose of procreation, we shall find that the movements of the males are subject to a very definite routine. This, however, is not true of every male; some may be wending their way to breeding grounds at a distance; others may be seeking the particular environment to which they may be adapted; others again, having found their old haunts destroyed, may consequently be seeking new.
Of all this there is evidence. Small parties of Chiffchaffs pass through a district on their way to other breeding grounds, flitting from hedge to hedge as they move in a definite direction with apparently a definite purpose; Reed-Warblers settle in a garden or plantation, eminently unsuited to their requirements, and disappear; Wood-Warblers arrive in some old haunt, and finding it no longer suitable for their purpose, seek new ground. So that plenty of individuals are always to be found, which, for the time being at least, are wanderers.
In the district which I have in mind, the wandering males form only a small part of the incoming bird population. The majority of individuals that fall under observation are those that have made this particular district their destination; and in doing so, they may possibly have been guided by their experience as owners or inmates of former nests, for it cannot be doubted that a return to the neighbourhood of the birthplace would lead to a more uniform distribution and therefore be advantageous, and the tendency to do so might consequently have become interwoven in the tissue of the race. How, then, do they behave? A certain amount of movement, an interchanging of positions, even though restricted to an area defined, let us say, by experience, might be expected under the circumstances—that, however, is not what we find; we observe the available situations plotted out into so many territories, each one of which is occupied by a male who passes the whole of his time therein. Take whatever species we will—Whitethroat, Whinchat, Willow-Warbler, Red-backed Shrike, it matters not which, for there is no essential difference in the general course of procedure—this condition will be found to prevail. Generally speaking, the behaviour in relation to the territory can be studied more conveniently where a number of individuals of the same species have established themselves in proximity to one another. Such species as the Chiffchaff, Willow-Warbler, or Wood-Warbler are often sufficiently common to allow of three or more of their respective males being kept in view at the same time; and the disposition to occupy a definite position can be readily observed. The Reed-Warbler is a suitable subject for an investigation of this kind; for since it is restricted by its habits to localities wherein the common reed (Arundo phragmites) grows in abundance, and since such localities are none too plentiful and often limited in extent, the area occupied by each individual is necessarily small—if it were not so the species would become extinct. Hence it is a simple matter to study the routine of the different individuals and to mark the extent of their wanderings.
In this way the males of all the Warblers that breed commonly in Great Britain establish themselves, each one in its respective station at the respective breeding ground; so, too, do those of many other migrants—for example, the Whinchat, Wheatear, Tree-Pipit, and Red-backed Shrike. All of these, it is true, are common species—numbers of individuals can often be found in close proximity—and therefore it may be argued that they keep to one position more from pressure of population than from any inherited disposition working towards that end. But the rarer species behave similarly. Districts frequented by the Marsh-Warbler and offering plenty of situations of the type required by the bird are often inhabited by a few members only, and yet the disposition to remain in a definite position is just as marked.
You will say, however, that these smaller migrants have no exceptional powers of flight; that they have besides just completed a long and arduous journey; and you will ask why they should be expected to wander, whether it is not more reasonable to expect that, in order to overcome their fatigue, they should remain where they settle. The Cuckoo is a wanderer in the wider sense of the term, and is gifted with considerable powers of flight. Upon arrival the male flies briskly from field to field, showing but little signs of weariness; yet we have only to follow its movements for a few days in succession to assure ourselves that the bird is no longer a wanderer; for just as the Warbler or the Chat moves only within a definitely delimited area, so the male Cuckoo, strange as it may seem, restricts itself to a particular tract of land. The area over which it wanders is often considerable and consequently it is not possible to keep the bird always in view, but inasmuch as the variation in the voices of different individuals is quite appreciable, identification is really a simple matter. If we cannot keep the bird in sight, we can trace its movements by sound and mark the extent of its wanderings, which by repetition become more and more defined, until a belt of trees here, or an orchard there, mark a rough and rarely passed boundary line.
Let us take another example from the larger migrants—the Black-tailed Godwit, a bird common enough in the Dutch marshes but no longer breeding in this country. On suitable stretches of marsh land, numbers will be found in proximity one to another after the manner of the Lapwing, each male occupying a definite space of ground wherein it passes the time preening, searching for food, or in sleep—though at the same time keeping a strict watch over its territory. Now the preference shown for a particular piece of ground, and the determination with which it is resorted to, is the more remarkable when we take into consideration the specific emotional behaviour arising from the seasonal sexual condition. This behaviour is expressed in a peculiar flight. The bird rises high in the air, circles round with slowly beating wings above the marsh, and utters a call which, as far as my experience goes, is characteristic of the performance. The air is often full of individuals circling thus even beyond the confines of the marsh, for a male does not limit its flight to a space immediately above its territory; but nevertheless careful observation will show how unerringly each one returns to its own position on the breeding ground, no matter how extensive the aerial excursion may have been. And so, when the males of the smaller migrants confine their movements to an acre of ground at the completion of their long journey, they are acting no more under the influence of fatigue than the Cuckoo, which keeps within certain bounds yet flies about briskly, or the Godwit which, though holding to its few square yards on the ground, executes most tiring and extensive flights above the marsh.
Of all the migrants, however, the behaviour of the Ruff is perhaps the most strange, and though it has long been known that these birds have their special meeting places where they perform antics and engage in serious strife, yet it is only within recent years that the primary purpose of these gatherings has been ascertained—that purpose being the actual discharge of the sexual function. Mr. Edmund Selous has carried out some exhaustive investigations into their activities at the meeting places, and he makes it clear that each bird has its allotted position. He says, for example, that "It begins to look as though different birds had little seraglios of their own in different parts of the ground," that "each Ruff has certainly a place of its own," or again that "this Ruff indeed, which I think must be a tender-foot, does not seem to have a place of its own like the others." Nevertheless it is only at the meeting places that they have their special positions; there is no evidence to show that each one has a special territory, wherein it seeks its food, as the Warbler has, and therefore some may think that we are here confronted with behaviour of a different order. But we must bear in mind that the process has been adjusted to meet the requirements of different species: the size of the territory, the period of its daily occupation, the purpose which it serves—these all depend upon manifold relationships and do not affect the principle. Why it has been differentiated in different circumstances we shall have occasion to discuss later; for the moment it is enough that at the end of its migratory journey each Ruff occupies one position on the meeting ground.
Now birds that are paired for life, whose food-supply is not affected by alternations of climate, have no occasion to desert the locality wherein they have reared their offspring, and so their movements, being subject to a routine which would tend to become increasingly definite, must in the course of time and according to the law of habit formation become organised into the behaviour we observe. Is it necessary, therefore, to seek an explanation of their tendency to remain in one place in anything so complex as an inherited disposition? Again, since we have to confess to so very much ignorance on so many points connected with the whole phenomenon of migration, may there not be some condition, hitherto shrouded in mystery, which might place so different a complexion on the corresponding aspect of migrant behaviour as to rid us, in their case also, of the necessity of appealing to an inherited disposition? Such questions are justifiable. And if the life-histories of other species gave no further support to our interpretation, if, in short, the evidence were to break down at this point, then we should be forced to seek some other explanation more in keeping with the general body of facts.
But far from placing any obstacle in the way of an interpretation in terms of inherited disposition, the behaviour of many of those residents which are not paired for life gives us even surer ground for that belief. Moreover in their case the initial stages in the process are more accessible to observation. I will endeavour to explain why. In the process of reproduction the environment has its part to play—whether in the manner here suggested, or indirectly through the question of food-supply, matters not at the moment. Now, migratory species are more highly specialised than resident species as regards food, and are affected more by variations of temperature, so that they can live for only a part of the year in the countries which they visit for the purpose of procreation. Hence the organic changes, which set the whole process in motion, must be coincident in time with the growth of appropriate conditions in the environment; for if it were not so, if the internal organic changes were to develop prematurely, the bird would undertake its journey only to find an insufficiency of food upon its arrival, and this would scarcely contribute towards survival. Definite limitations have therefore been imposed upon the period of organic change. But in the case of many resident species the conditions are somewhat different, for they remain in the same locality throughout the year, and a gradual unfolding of the reproductive process cannot therefore have a similarly harmful effect. Thus it comes about that the behaviour of the migrant, when it arrives at the breeding ground and first falls under observation, represents a stage in the process which, in the case of the resident, is only reached by slow degrees; and by closely observing the behaviour as it is presented to us in the life of the resident male, we not only gain a better insight into the changes in operation, but can actually witness the breaking down of the winter routine, stereotyped through repetition, by the new disposition as it arises.
The first visible manifestations, even though they may be characterised by a certain amount of vagueness, are therefore of great importance if the behaviour is to be interpreted aright; and in order to insure that none of these earlier symptoms shall be missed, it is necessary to begin the daily record of the bird's movements at an early date in the season. As a rule the second week in February is sufficiently early for the purpose, but the date varies according to the prevailing climatic conditions. Even in species widely remote there is great similarity of procedure, and the behaviour of the Buntings is typical of that of many. With the rise of the appropriate organic state the male resorts at daybreak to a suitable environment, occupies a definite position, and singling out some tree or prominent bush, which will serve as a headquarters, advertises its presence there by song. At first the bird restricts its visits, which though frequent in occurrence are of short duration, for the most part to the early hours of the morning; it disappears as suddenly as it appeared, and one can trace its flight to the feeding grounds—a homestead or perhaps some newly sown field. But by degrees the impulse to seek the society of the flock grows less and less pronounced, the visits to the territory are more and more prolonged, and the occupation of it then becomes the outstanding feature of the bird's existence. This in outline is the course of procedure as it appears to an external observer.
But although much can be learnt from the lives of these smaller species, there is no gain-saying the fact that a great deal of patient observation is required, and the process is apt to become tedious. There are others, however, which are more readily observed, whilst their life-histories afford just as clear an insight into the effect produced by the new disposition upon the developing situation; and among these the Lapwing takes a prominent position, because it is plentiful and inhabits open ground where it is easily kept in view.
Plans of the Water-meadow showing the Territories occupied by Lapwings in 1915.
Plans of the Water-meadow showing the Territories occupied by Lapwings in 1916
There is a water meadow with which I am familiar, where large numbers resort annually for the purpose of procreation. Here they begin to arrive towards the end of February, and at first collect in a small flock at one end of the meadow. A male, here and there, can then be seen to break away from the flock, and to establish itself in a definite position upon the unoccupied portion of the ground, where it remains isolated from its companions. Others do likewise until the greater part of the meadow is divided into territories. Six of these territories I kept under observation for approximately two months in the year 1915. The occupant of the one marked No. 6 upon the 1915 plan was a lame bird, a fortunate occurrence as it enabled me to follow its movements with some accuracy; and though it maintained its position for some weeks, it ultimately disappeared, as a result, I believe, of the persistent attacks of neighbouring males. The behaviour of the males during the first fortnight or so after they broke away from the flock was interesting. Though they retired to their territories and remained in them for the greater part of their time, yet it was only by degrees that they finally severed their connection with the flock, for so long as a nucleus of a flock remained, so long were they liable to desert their territories temporarily and to rejoin their companions.
Lapwings, as is well known, collect in flocks during the winter months, and these flocks, which sometimes reach vast proportions, are to be found on tidal estuaries, water meadows, arable land, and such like places, according to the prevailing climatic conditions. This flocking may contribute towards survival, and may therefore be the result of congenital dispositions which have been determined on biological grounds. On the other hand, since food at that season is only to be obtained in a limited number of situations, the birds may be simply drawn together by accident. In the former case the behaviour would be instinctive, in the latter, though accidental at first, recurrent repetition would tend to make it habitual; but in either case the impulse to accompany the flock must be a powerful one, for on the one hand it would depend upon inherited, and on the other hand upon acquired, connections in the nervous system. Now observe that soon after the flock arrived in the meadow, single males detached themselves; there was no hesitation, they just retired from their companions and settled in their respective territories. They were not expelled, for if their leaving had been compulsory much commotion would have preceded their departure, and their return would certainly not have been welcomed. A reference to the plan will make the position clearer; the neutral zone inhabited by the flock is there shown as situated in one corner of the meadow, the territories that fell under observation are plotted out as far as possible to scale, and the more important zones of conflict are also marked.
The males spent part of their time in their respective territories and part with the flock, so long as it remained in existence. When a male was in its territory it avoided companions and was openly hostile to intruders; when it was with the flock it wandered about with companions in search of food. The contrast between the two modes of behaviour was very marked, and it was evident that the gregarious instinct was gradually yielding its position of importance to the new factor—the territory. If there had been no flock, if a few solitary individuals had appeared here and there and had established themselves in different parts of the meadow, one would have had no definite evidence of the strength of the impulse in the male to seek a position of its own, one could only have argued from the general fact of males flocking in the winter and isolating themselves in spring that something more than accident was required to explain so radical a change. But since the birds returned in a flock to the ground upon which they intended to breed, and since the flock occupied temporarily part of the ground whilst the partitioning of the remainder was still proceeding, it was possible to gauge the strength of the impulse, which was forcing the males to isolate themselves in particular areas of ground, by comparing it with the impulse to accompany the flock—and the measure of its intensity was the rapidity with which the latter impulse yielded its position of importance.
Like the Lapwing, the Coot and Moor-Hen are easily kept under observation, and since many individuals often breed in proximity, more than one can be watched at the same moment; moreover the area occupied by each male generally embraces an open piece of water as well as part of the fringe of reeds, so that the movements of the bird can be followed without much difficulty. Under favourable conditions manifestations of the developing situation become visible at a comparatively early date in the season—the middle or the latter part of February—and these manifestations resemble those of other species. But the Moor-Hen passes summer and winter alike in the same situation, and being therefore in a position to respond at once to internal stimulation, however vague, the change from the one state to the other is gradual. This, however, is a matter of detail; the main consideration lies in the fact that the impulse to retire to a definite position, to avoid companions, and to live in seclusion, is strongly marked, and produces a type of behaviour similar on the whole to that of the Lapwing. First of all there is the appropriation of a certain position, the limits of which are fixed according to the law of habit formation, and according to the pressure exerted by neighbouring individuals; then there is the neutral ground over which the birds wander amicably in search of food; and finally there is the contrast between the pugnacity of the male whilst in its territory, and its comparative friendliness when upon neutral ground.
Evidence of similar behaviour is to be found in the life of the Black Grouse, a bird which has always excited the curiosity of naturalists on account of the special meeting places to which both sexes resort in the spring. Mr. Edmund Selous watched these birds in Scandinavia, where he kept a daily record at one of the meeting places. In various passages he refers to the appropriation of particular positions by particular males, and concludes thus: "It would seem from this that, like the Ruffs, each male Blackcock has its particular domain on the assembly ground, though the size of this is in proportion to the much greater space of the whole. On the other mornings, too, the same birds, as I now make no doubt they are, have flown down into approximately the same areas."
The cliff-breeding species—Guillemots, Razorbills, and Puffins—are difficult to investigate because individuals vary so little, and the sexes resemble one another so closely; yet, despite these difficulties, we can gain some idea of the general purport of their activities. But when the ledges are crowded and the air is filled with countless multitudes, how is it possible to keep a single bird in view for a sufficient length of time to understand its routine? The difficulty is not an insuperable one. The flights, undertaken seemingly for no particular purpose, are often of short duration and are completed before the strain of observation becomes too great; moreover an individual sometimes possesses a special mark or characteristic which serves to make it conspicuous. For example, there is a well-marked variety of the Common Guillemot, the Ringed or Bridled Guillemot of science, distinguished by an unusual development of white round the eye and along the furrow behind it. One such individual I was fortunate in discovering upon a crowded cliff, and, as in the case of the Lapwing with the broken leg or the Yellow Bunting with the injured foot, the identity of the bird was beyond dispute, and one could observe that it appropriated to itself a particular position upon a particular ledge.
Guillemots and Razorbills return at intervals to the breeding stations early in the season, and these visits are repeated with growing frequency until the birds are finally established. I have witnessed these periodic returns during March in the south of England, and during April in the north-west of Ireland, and I am informed that in the latter district such visits may occur as early as February. Gätke, who had ample opportunity of observing the birds in Heligoland, puts their return at an even earlier date. "They visit their breeding places," he says, "in flocks of thousands at the New Year, often even as early as December, as though they wanted to make sure of their former haunts being well preserved and ready for their reception." Such visits, however, are irregular in occurrence; the birds arrive, and, after spending a short time upon the ledges, disappear. And since there is not the same evidence in their coming and going of that method which we observe in the periodical returns of the Bunting or the Finch, it may be thought that needless importance is being attached to an episode in their lives which is quite intelligible in terms of a feeble response determined by a dawning organic change. While it may be quite intelligible in such terms it is not thereby explained; for every response must have as its antecedent an inherited connection in the nervous system determined on biological grounds. Besides, these early periodic returns conform in general to the type of behaviour displayed by other species, the males of which return to their breeding grounds many weeks before the real business of reproduction begins. Are we then justified in regarding them as accidents of the developing situation? Are we not rather bound to admit that they have some definite biological end to serve?
These examples show that the males of many species reverse their mode of life at the commencement of the breeding season and proceed to isolate themselves, each one in a definitely delimited area.
There are three ways in which we may attempt to interpret this particular mode of male behaviour. We may regard it as an accidental circumstance, nowise influencing the course of subsequent procedure; or, appealing to the law of habit formation, we may regard it as an individual acquirement; or again, we may invest it with a deeper significance and seek its origin in some specific congenital disposition determined on purely biological grounds.
Which of these three shall we choose? The first by itself requires but little consideration; for though it might explain the initial visit, it cannot account for the persistency with which the plot of ground is afterwards resorted to. Supposing, however, that we combine the first and the second; supposing, that is to say, we assume, for the purpose of argument, that the initial visit is fortuitous, and that constancy is supplied by habit formation—would that be a satisfactory interpretation? It is a simple one, inasmuch as it only requires that a male shall alight by chance in a particular place for a few mornings in succession in order that the process may be set in motion. Now an essential condition of habit formation is recurrent repetition; given this repetition and, it is true, any mode of activity is liable to become firmly established. But how can we explain the repetition? Even if we are justified in assuming that the initial visit is purely an accidental occurrence, we cannot presume too far upon the laws of chance and assume that the repetition, at first, is also fortuitous.
So that we come back to the congenital basis, the last of our three propositions. And it will, I think, be admitted that the facts give us some grounds for believing that the securing of the territory has its root in the inherited constitution of the bird. In comparing the behaviour of the migratory male with that of the resident, attention was drawn to the manner in which the occupation of a territory was effected: the former bird, it may be remembered, established itself without delay, whereas the latter did so only by degrees, and the difference was attributed to the incidence of migration which required a closer correspondence between organic process and external environment. But the significance for us just now lies in the fact that the definiteness, which accompanies the initial behaviour of the migratory male in relation to the territory, cannot have been acquired by repetition; for this reason, that when the male occupies its space of ground at the end of its long and arduous journey, it does so without preparation or experiment, even without hesitation, as if aware that it was making good the first step in the process of reproduction. No doubt, if it happened to be an individual that had already experienced the enjoyment of reproduction, it might be aware of the immediate results to be achieved and act accordingly. But among the hosts of migrants that one observes, there must be many males which have not previously mated; and yet, upon arrival, they all behave in a similarly definite manner—so that experience cannot well be the primary factor in the situation. If, then, the essential condition of habit formation is absent and experience is eliminated, there is nothing left but racial preparation to fall back upon.
Nevertheless, it is true that many resident males seem to pass through a period of indecision before they establish themselves permanently in their respective territories; they come and go, their visits grow more and more prolonged, and only after the lapse of some considerable time does the process of establishment attain that degree of completeness which is represented in the initial behaviour of the migratory male. Their whole procedure seems therefore to bear the stamp of individual acquirement; and, if it stood alone, we might be content to construe it thus, but the example of the migratory male necessitates our looking elsewhere for the real meaning of the indecision.
Let me first of all give some instances of the persistence with which a male remains in one spot, and this despite the fact that it has no mate.
A Reed-Bunting occupied a central territory in a strip of marshy ground inhabited annually by four or five males of this species. Throughout April, May, and until the 19th June, it clung to its small plot of ground, tolerated no intrusion, and sang incessantly.
Two Whitethroats arrived at much the same time—the 30th April approximately—and occupied the corner of a small plantation; the one obtained a mate the day following its arrival, the other remained unpaired for a fortnight.
A Reed-Warbler established itself amongst some willows and alders adjoining a reed-bed and made its headquarters in a small willow bush. Not more than fifteen yards away, on the edge of the main portion of the reeds, another male was established and was paired on the 22nd May. Each morning the single male behaved in much the same way, singing continuously whilst perched upon the bush. And so the days passed by until it seemed improbable that it would ever secure a mate, but one appeared on the 20th June, and a nest was built forthwith.
Now it is difficult to believe that a chance visit, even though repeated for a few mornings in succession, could have accounted for the Reed-Bunting remaining so persistently in the marsh, or the Whitethroat in one corner of the osier bed, or the Reed-Warbler in that one particular willow. Not only so, but if a habit of such evident strength can be acquired so readily, we have a right to ask why it should only be acquired in the spring—why not at every season? Considerations such as these lead to the belief that there must be some congenital basis to account for such persistent endeavour; the more so since it is difficult not to be impressed with the conative aspect of the male's behaviour. To a stranger, unacquainted with its previous history, the bird might appear to be leading a life of hesitation, whereas, if carefully watched, its whole attitude will be found to betray symptoms of a striving towards some end; and the frequent departure and return, which might be pointed to as the material from which a definite mode of procedure would be likely to emerge, is in reality behaviour of a determinate sort.
My interpretation, then, of the apparent indecision in the behaviour of the resident male is this. During the winter most species live in societies, together they seek their food and together they retire in the evening to the accustomed roosting places; and the association of different individuals confers mutual benefits upon the associates. The movements of these societies are dominated by the question of food; all else is subservient, and the supply of the necessary sustenance may, under certain conditions, become a difficulty which can only be met by energy and resource. After the long night the sensation of hunger is strong, and the birds, on awakening, fly to the accustomed feeding grounds, returning again in the evening to the selected spot, and by frequent repetition a routine becomes established. Thus the behaviour of each individual is determined not only by the powerful gregarious impulse but also by the habits formed in connection therewith during many weeks in succession. Now with the rise of the appropriate organic state, the disposition to seek the breeding ground and there to establish itself becomes dominant in the male. But the process is a gradual one. There is no need, as happens amongst the migrants, for the period of organic change to conform rigidly to the growth of any particular condition in the environment, and hence for a time the bird oscillates between two modes of behaviour—between that one organised by frequent repetition and that one determined by the functioning of this new disposition.
To look at the matter broadly, it is scarcely likely that so definite a mode of behaviour would recur with such regularity, generation after generation, in the individuals belonging to so many widely divergent forms, if it had no root in the inborn constitution of the bird. But the law of habit formation has its part to play also. By itself it is inadequate; yet it probably does assist very materially in adding still greater definition, and it probably is responsible in a large measure for determining the limits of the territory according to the conditions of existence of the species—thus the Falcon seeks its prey over wide tracts of land, and, by hunting over certain ground repeatedly, establishes a routine, which broadly fixes the area occupied; the Woodpecker cannot find food upon every tree, and every forest does not contain the necessary trees, and therefore the bird regulates its flight according to the position of the trees; and the Warbler, finding food close at hand, does not need to travel far, and the area it occupies is consequently small.
So that the most likely solution of the problem will be found in a combination of our second and third propositions; that is to say, in an initial responsive behaviour provided for in the inherited constitution of the nervous system, and in a definiteness acquired by repetition and determined by relationships in the external environment.
CHAPTER III
THE DISPOSITION TO DEFEND THE TERRITORY
In the previous chapter I endeavoured to show that each male establishes a territory at the commencement of the breeding season, and there isolates itself from members of its own sex. And further I gave my reasons for believing that this particular mode of behaviour is determined by the inherited nature of the bird, and that we are justified in speaking of it as "a disposition to secure a territory" because we can perceive its prospective value. But the act of establishment is only one step towards "securing." By itself it can achieve nothing; for any number of different individuals might fix upon the same situation, and if there were nothing in the inherited constitution of the bird to prevent this happening, where would be the security, or how could any benefit accrue to the species?
In withdrawing from its companions in the spring, the male is breaking with the past, and this action marks a definite change in its routine of existence. But the change does not end in attempted isolation; it is carried farther and extends to the innermost life and affects what, humanly speaking, we should term its emotional nature, so that the bird becomes openly hostile towards other males with whom previously it had lived on amicable terms.
The seasonal organic condition is responsible for the functioning of the disposition which results in this intolerance, just as it is for the functioning of the disposition which leads to the establishment of the territory; and the effect of these two dispositions is that a space of ground is not only occupied but made secure from intrusion. The process is a simple one. There is no reason to believe, there is no necessity to believe, that any part of the procedure is conditioned by anticipatory meaning; the behaviour is "instinctive" in Professor Lloyd Morgan's definition of the word, since it is of a "specific congenital type, dependent upon purely biological conditions, nowise guided by conscious experience though affording data for the life of consciousness."
That the males of many animals are apt to become quarrelsome during the mating period is notorious. Darwin collected a number of facts, many of which related to birds, showing the nature and extent of the strife when the sexual instinct dominated the situation. And pondering over these facts, he deduced therefrom a "law of battle," which, he believed, bore a direct relation to the possession of a female. And it must be admitted that he had excellent ground for his conclusion in the fact not only that the conflicts occur mainly during the pairing season, but that the female is often a spectator and seems even to pair with the victor. I accepted it, therefore, as the most reasonable interpretation of the facts. But, as time passed by, incidents of a conflicting character led me to think that after all there might be another solution of the problem. And when it was no longer possible to doubt that there was a widespread tendency to establish territories, it at once became manifest that the battles might have an important part to play in the whole scheme. But how was this to be proved? What sort of evidence could show whether the proximate end for which the males were fighting had reference to the female or to the territory? Clearly nothing but a complete record of the whole series of events leading up to reproduction could supply the necessary data upon which a decision might rest. In the present chapter I shall give, in the first place, the reasons which lead me to think that the origin of the fighting cannot be traced to the female; afterwards, the evidence which seems to show that it must be sought in the territory; and finally, I shall make a suggestion as to the part the female may play in the whole scheme.