Territory in Bird Life.

by H. Eliot Howard.

PREFACE

When studying the Warblers some twenty years ago, I became aware of the fact that each male isolates itself at the commencement of the breeding season and exercises dominion over a restricted area of ground. Further investigation, pursued with a view to ascertaining the relation of this particular mode of behaviour to the system of reproduction, led to my studying various species, not only those of close affinity, but those widely remote in the tree of avian life. The present work is the outcome of those investigations. In it I have endeavoured to interpret the prospective value of the behaviour, and to trace out the relationships in the organic and inorganic world which have determined its survival.

Much is mere speculation; much with fuller knowledge may be found to be wrong. But I venture to hope that a nucleus will remain upon which a more complete territorial system may one day be established.

I have to thank Mr. G. E. Lodge and Mr. H. Gronvold for the trouble they have taken in executing my wishes; I also want to record my indebtedness to the late E. W. Hopewell; and to Professor Lloyd Morgan, F.R.S., I am beholden more than I can tell.

CHAPTER I

INTRODUCTION

In his _Manual of Psychology_ Dr Stout reminds us that "Human language is especially constructed to describe the mental states of human beings, and this means that it is especially constructed so as to mislead us when we attempt to describe the working of minds that differ in a great degree from the human."

The use of the word "territory" in connection with the s.e.xual life of birds is open to the danger which we are here asked to guard against, and I propose, therefore, before attempting to establish the theory on general grounds, to give some explanation of what the word is intended to represent and some account of the exact position that representation is supposed to occupy in the drama of bird life.

The word is capable of much expansion. There cannot be territories without boundaries of some description; there cannot well be boundaries without disputes arising as to those boundaries; nor, one would imagine, can there be disputes without consciousness as a factor entering into the situation; and so on, until by a simple mental process we conceive of a state in bird life a.n.a.logous to that which we know to be customary amongst ourselves. Now, although the term "breeding territory," when applied to the s.e.xual life of birds, is not altogether a happy one, it is difficult to know how otherwise to give expression to the facts observed. Let it then be clearly understood that the expression "securing a territory" is used to denote a process, or rather part of a process, which, in order to insure success to the individual in the attainment of reproduction, has been gradually evolved to meet the exigencies of diverse circ.u.mstances. Regarded thus, we avoid the risk of conceiving of the act of securing a territory as a detached event in the life of a bird, and avoid, I hope, the risk of a conception based upon the meaning of the word when used to describe human as opposed to animal procedure.

Success in the attainment of reproduction is rightly considered to be the goal towards which many processes in nature are tending. But what is meant by success? Is it determined by the actual discharge of the s.e.xual function? So many and so wonderful are the contrivances which have slowly been evolved to insure this discharge, that it is scarcely surprising to find attention focused upon this one aspect of the problem. Yet a moment's reflection will show that so limited a definition of the term "success" can only be held to apply to certain forms of life; for where the young have to be cared for, fostered, and protected from molestation for periods of varying lengths, the actual discharge of the s.e.xual function marks but one stage in a process which can only succeed if all the contributory factors adequately meet the essential conditions of the continuance of the species.

Securing a territory is then part of a process which has for its goal the successful rearing of offspring. In this process the functioning of the primary impulse, the acquirement of a place suitable for breeding purposes, the advent of a female, the discharge of the s.e.xual function, the construction of the nest, and the rearing of offspring follow one another in orderly sequence. But since we know so little of the organic changes which determine s.e.xual behaviour, and have no means of ascertaining the nature of the impulse which is first aroused, we can only deal with the situation from the point at which the internal organic changes reflect themselves in the behaviour to a degree which is visible to an external observer. That point is reached when large numbers of species, forsaking the normal routine of existence to which they have been accustomed for some months, suddenly adopt a radical change in their mode of behaviour. How is this change made known to us?

By vast numbers of individuals hurrying from one part of the globe to another, from one country to another, and even from mid-ocean to the coasts; by detachments travelling from one district to another; by isolated individuals deserting this place for that; by all those movements, in fact, which the term migration, widely applied, is held to denote. Now the impulse which prompts these travelling hosts must be similar in kind whether the journey be long or short; and it were better, one would think, to regard such movements as a whole than to fix the attention on some one particular journey which fills us with amazement on account of the magnitude of the distance traversed or the nature of the difficulties overcome. For, after all, what does each individual seek? There may be some immature birds which, though they have not reached the necessary stage of development, happen to fall in with others in whom the impulse is strong and are led by them--they know not where. But the majority seek neither continent nor country, neither district nor locality is their aim, but a place wherein the rearing of offspring can be safely accomplished; and the search for this place is the earliest visible manifestation in many species of the reawakening of the s.e.xual instinct.

The movements of each individual are then directed towards a similar goal, namely, the occupation of a definite station; and this involves for many species a distinct change in the routine of behaviour to which previously they had been accustomed. Observe, for example, one of the numerous flocks of Finches that roam about the fields throughout the winter. Though it may be composed of large numbers of individuals of different kinds, yet the various units form an amicable society actuated by one motive--the procuring of food. And since it is to the advantage of all that the individual should be subordinated to the welfare of the community as a whole there is no dissension, apart from an occasional quarrel here and there.

In response, however, to some internal organic change, which occurs early in the season, individuality emerges as a factor in the developing situation, and one by one the males betake themselves to secluded positions, where each one, occupying a limited area, isolates itself from companions. Thereafter we no longer find that certain fields are tenanted by flocks of greater or less dimensions, while acres of land are uninhabited, but we observe that the hedgerows and thickets are divided up into so many territories, each one of which contains its owner. This procedure, with of course varying detail, is typical of that of many species that breed in Western Europe. And since such a radical departure from the normal routine of behaviour could scarcely appear generation after generation in so many widely divergent forms, and still be so uniform in occurrence each returning season, if it were not founded upon some congenital basis, it is probable that the journey, whether it be the extensive one of the Warbler or the short one of the Reed-Bunting, is undertaken in response to some inherited disposition, and probable also that the disposition bears some relation to the few acres in which the bird ultimately finds a resting place. Whilst for the purpose of the theory I shall give expression to this behaviour in terms of that theory, and speak of it as a disposition to secure a territory, using the word disposition, which has been rendered current in recent discussion, for that part of the inherited nature which has been organised to subserve a specific biological purpose--strict compliance with the rules of psychological a.n.a.lysis requires a simpler definition; let us therefore say "disposition to remain in a particular place in a particular environment."

But even granting that this disposition forms part of the hereditary equipment of the bird, how is the process of reproduction furthered? The mere fact of remaining in or about a particular spot cannot render the attainment of reproduction any less arduous, and may indeed add to the difficulties, for any number of individuals might congregate together and mutually affect one another's interests. A second disposition comes, however, into functional activity at much the same stage of s.e.xual development, and manifests itself in the male's intolerance of other individuals. And the two combined open up an avenue through which the individual can approach the goal of reproduction. In terms of the theory I shall refer to this second disposition as the one which is concerned with the defence of the territory.

Broadly speaking, these two dispositions may be regarded as the basis upon which the breeding territory is founded. Yet inasmuch as the survival value of the dispositions themselves must have depended upon the success of the process as a whole, it is manifest that peculiar significance must not be attached to just the area occupied, which happens to be so susceptible of observation; other contributory factors must also receive attention, for the process is but an order of relationships in which the various units have each had their share in determining the nature and course of subsequent process, so that, as Dr Stout says, when they were modified, it was modified.

Now the male inherits a disposition which leads it to remain in a restricted area, but the disposition cannot determine the extent of that area. How then are the boundaries fixed? That they are sometimes adhered to with remarkable precision, that they can only be encroached upon at the risk of a conflict--all of this can be observed with little difficulty. But if we regard them as so many lines definitely delimiting an area of which the bird is cognisant, we place the whole behaviour on a different level of mental development, and incidentally alter the complexion of the whole process. It would be a mistake, I think, to do this. Though conscious intention as a factor may enter the situation, there is no necessity for it to do so; there is no necessity, that is to say, for the bird to form a mental image of the area to be occupied and shape its course accordingly. The same result can be obtained without our having recourse to so complex a principle of explanation, and that by the law of habit formation. In common with other animals, birds are subject to this law in a marked degree. An acquired mode of activity becomes by repet.i.tion ingrained in the life of the individual, so that an action performed to-day is liable to be repeated to-morrow so long as it does not prejudice the existence or annul the fertility of the individual.

Let us see how this may have operated in determining the limits of the area acquired, and for this purpose let us suppose that we are observing a male Reed-Bunting recently established in some secluded piece of marsh land. Scattered about this particular marsh are a number of small willows and young alder trees, each one of which is capable of providing plenty of branches suitable for the bird to perch upon, and all are in a like favourable position so far as the outlook therefrom is concerned.

Well, we should expect to find that each respective tree would be made use of according to the position in which the bird happened to find itself. But what actually do we find--one tree singled out and resorted to with ever-increasing certainty until it becomes an important point in relation to the occupied area, a headquarters from which the bird advertises its presence by song, keeps watch upon the movements of its neighbours, and sets out for the purpose of securing food. We then take note of its wanderings in the immediate vicinity of the headquarters, especially as regards the direction, frequency, and extent of the journeys; and we discover not only that these journeys proceed from and terminate in the special tree, but that there is a sameness about the actual path that is followed. The bird takes a short flight, searches a bush here and some rushes there, returns, and after a while repeats the performance; we on our part mark the extreme limits reached in each direction, and by continued observation discover that these limits are seldom exceeded, that definition grows more and more p.r.o.nounced, and that by degrees the movements of the bird are confined within a restricted area. In outline, this is what happens in a host of cases. By repet.i.tion certain performances become stereotyped, certain paths fixed, and a routine is thus established which becomes increasingly definite as the season advances.

But while it would be quite untrue to say that this routine is never departed from, and equally profitless to attempt to find a point beyond which the bird will under no circ.u.mstances wander, yet there is enough definition and more than enough to answer the purpose for which the territory has, I believe, been evolved, that is to say the biological end of reproduction. Again, however, the process of adjustment is a complex one. Habit plays its part in determining the boundaries in a rough and ready manner, but the congenital basis, which is to be found in the behaviour adapted to a particular environment, is an important factor in the situation. For example, if instead of resting content with just a bare position sufficient for the purpose of reproduction, the Guillemot were to hustle its neighbours from adjoining ledges, the Guillemot as a species would probably disappear; or if instead of securing an area capable of supplying sufficient food both for itself and its young, the Chiffchaff were to confine itself to a single tree, and, after the manner of the Guillemot, trust to spasmodic excursions into neutral ground for the purpose of obtaining food, the Chiffchaff as a species would probably not endure. All such adjustments have, however, been brought about by relationships which have gradually become interwoven in the tissue of the race.

The intolerance that the male displays towards other individuals, usually of the same s.e.x, leads to a vast amount of strife. Nowhere in the animal world are conflicts more frequent, more prolonged, and more determined than in the s.e.xual life of birds; and though they are acknowledged to be an important factor in the life of the individual, yet there is much difference of opinion as to the exact position they occupy in the drama of bird life. Partly because they frequently happen to be in evidence, partly because they are numerically inferior, and partly, I suppose, because the compet.i.tion thus created would be a means of maintaining efficiency, the females, by common consent, are supposed to supply the condition under which the pugnacious nature of the male is rendered susceptible to appropriate stimulation. And so long as the evidence seemed to show that battles were confined to the male s.e.x, so long were there grounds for hoping that their origin might be traced to such compet.i.tion. But female fights with female, pair with pair, and, which is still more remarkable, a pair will attack a single male or a single female; moreover, males that reach their destination in advance of their prospective mates engage in serious warfare. How then is it possible to look upon the individuals of one s.e.x as directly responsible for the strife amongst those of the other, or how can the female supply the necessary condition? As long as an attempt is made to explain it in terms of the female, the fighting will appear to be of a confused order; regard it, however, as part of a larger process which demands, amongst other essential conditions of the breeding situation, the occupation of a definite territory, and order will reign in place of confusion.

But even supposing that the male inherits a disposition to acquire a suitable area, even supposing that it inherits a disposition which results indirectly in the defence of that area, how does it obtain a mate? If the female behaved in a like manner, if she, too, were to isolate herself and remain in one place definitely, that would only add to the difficulties of mutual discovery. We find, however, in the migrants, that the males are earlier than the females in reaching the breeding grounds, and, in resident species, that they desert the females and retire alone to their prospective territories, so that there is a difference in the behaviour of the s.e.xes at the very commencement of the s.e.xual process. What is the immediate consequence? Since the male isolates itself, it follows, if the union of the s.e.xes is to be effected, that the discovery of a mate must rest largely with the female. This of course reverses the accepted course of procedure. But after all, what reason is there to suppose that, the male seeks the female, or that a mutual search takes place; what reason to think that this part of the process is subject to no control except such as may be supplied by the laws of chance?

Now, clearly, much will depend upon the rapidity with which the female can discover a male fit to breed; for if the course of reproduction is to flow smoothly, there must be neither undue delay nor waste of energy incurred in the search--some guidance is therefore necessary, some control in her external environment. Here the song, or the mechanically produced sound, comes into play, and a.s.sists in the attainment of this end. Nevertheless if every male were to make use of its powers whether it were in occupation of a territory or not, if the wandering individual had an equal chance of attracting a mate, then it would be idle to attempt to establish any relation between "song" on the one hand, and "territory" on the other, and impossible to regard the voice as the medium through which an effectual union of the s.e.xes is procured. But there is reason to believe that the males utilise their powers of producing sound only under certain well-defined conditions. For instance, when they are on their way to the breeding grounds, or moving from locality to locality in search of isolation, or when they desert their territories temporarily, as certain of the residents often do, they are generally silent; but when they are in occupation of their territories they become vociferous--and this is notoriously the case during the early hours of the day, which is the period of maximum activity so far as s.e.xual behaviour is concerned. So that just at the moment when the s.e.xual impulse of the female is most susceptible to stimulation, the males are betraying their positions and are thus a guide to her movements. Nevertheless, even though she may have discovered a male ready to breed, success is not necessarily a.s.sured to her; for with mult.i.tudes of individuals striving to procreate their kind, it would be surprising if there were no clashing of interests, if no two females were ever to meet in the same occupied territory.

Compet.i.tion of this kind is not uncommon, and the final appeal is to the law of battle, just as an appeal to physical strength sometimes decides the question of the initial ownership of a territory.

I shall try to make clear the relations of the various parts to the whole with the a.s.sistance of whatever facts I can command. I shall do so not only for the purposes of the theory, but because one so often finds the more important features of s.e.xual behaviour regarded as so many distinct phenomena requiring separate treatment, whereas they are mutually dependent, and follow one another in ordered sequence. I spoke of the process as a series of relationships. Some of these relationships have already been touched upon; others will become apparent if we consider for a moment the purposes for which the territory has been evolved. Indirectly its purpose is that of the whole process, the rearing of offspring. But inasmuch as a certain measure of success could be attained, and that perhaps often, without all the complications introduced by the territory, there are manifestly advantages to be gained by its inclusion in the scheme. The difficulties which beset the path of reproduction are by no means always the same--all manner of adjustments have to be made to suit the needs of different species.

There are direct relationships, such as we have been speaking of, which are essential to the every-day working of the process, and others which are indirect, though none the less important for they must have exercised an influence throughout the ages. These latter are furnished by the physical--the inorganic world, by climate, by the supply of the particular kind of breeding stations, by the scarcity or abundance of the necessary food and by the relative position of the food supply to the places suitable for breeding. Why does the Reed-Bunting cling so tenaciously to an acre or more of marshy ground, while the Guillemot rests content with a few square feet on a particular ledge of rock? The answer is the same in both cases--to facilitate reproduction. But why should a small bird require so many square yards, whilst a very much larger one is satisfied with so small an area? The explanation must be sought in the conditions of existence. The Reed-Bunting has no difficulty in finding a position suitable for the construction of its nest; there are acres of waste land and reedy swamps capable of supplying food for large numbers of individuals, and the necessary situations for countless nests. But its young, like those of many another species, are born in a very helpless state. For all practical purposes they are without covering of any description and consequently require protection from the elements, warmth from the body of the brooding bird, and repeated supplies of nourishment. A threefold burden is thus imposed upon the parents: they must find food for themselves, they must afford protection to the young by brooding, and they must supply them with the necessary food at regular intervals. And their ability to do all this that is demanded of them will be severely taxed by the brooding which must perforce curtail the time available for the collection of food.

Let us then suppose that the Reed-Buntings inhabiting a certain piece of marsh are divided into two cla.s.ses, those which are pugnacious and intolerant of the approach of strangers, and those which welcome their presence. The nests of the former will be built in isolation, those of the latter in close proximity. In due course eggs will be laid and incubation performed, and thus far all alike will probably be successful. Here, however, a critical point is reached. If the young are to be freed from the risk of exposure, the parents must find the necessary supply of food rapidly. But manifestly all will not be in a like satisfactory position to accomplish this, for whereas the isolated pairs will have free access to all the food in the immediate vicinity of the nest, those which have built in proximity to one another, meeting compet.i.tion in every direction, will be compelled to roam farther afield and waste much valuable time by doing so; and under conditions which can well be imagined, even this slight loss of time will be sufficient to impede the growth of the delicate offspring, or to lead perhaps to still greater disaster. If any one doubts this, let him first examine one of the fragile offspring; let him then study the conditions under which it is reared, observing the proportion of time it pa.s.ses in sleep and the anxiety of the parent bird to brood; and finally let him picture to himself its plight in a wet season if, in order to collect the necessary food, the parents were obliged to absent themselves for periods of long duration.

Now take the case of the Guillemot. Its young at birth are by no means helpless in the sense that the young Reed-Bunting is, and food is readily procured. But breeding stations are scarce, for although there are many miles of cliff-bound coast, yet not every type of rock formation produces the fissures and ledges upon which the bird rests.

Hence vast stretches of coast-line remain uninhabited, and the birds are forced to concentrate at certain points, where year after year they a.s.semble in countless numbers from distant parts of the ocean. If, then, different individuals were to jostle one another from adjoining positions, and each one were to attempt to occupy a ledge in solitary State, not only would the successful ones gain no advantage from the additional s.p.a.ce over which they exercised dominion, but inasmuch as many members that were fitted to breed would be precluded from doing so, the status of the species as a whole would be seriously affected.

The amount of s.p.a.ce occupied by each individual is therefore a matter of urgent importance. A few square feet of rock sufficient for the immediate purpose of incubation is all that can be allowed if the species is to maintain its position in the struggle for existence.

Our difficulty in estimating the importance of the various factors that make for success or failure arises from our inability to see more than a small part of the scene as it slowly unfolds itself. The peculiar circ.u.mstances under which these cliff-breeding forms dwell does, however, enable us to picture, on the one hand, the precarious situation of an individual that was incapable of winning or holding a position at the accustomed breeding station, and, on the other, the plight of the species as a whole if each one exercised authority over too large an area. With the majority of species it is difficult to do this. So many square miles of suitable breeding ground are inhabited by so few Reed-Buntings that, even supposing certain members were to establish an ascendency over too wide an area, it would be impossible to discover by actual observation whether the race as a whole were being adversely affected. Compet.i.tion doubtless varies at different periods and in different districts according to the numerical standing of the species in a given locality and according to the numerical standing of others that require similar conditions of existence; at times it may even be absent, just as at any moment it may become acute. These examples show how profoundly the evolution of the breeding territory may have been influenced by relationships in the inorganic world, and they give some idea of the intricate nature of the problem with which we have to deal.

I mentioned that the first visible manifestation of the revival of the s.e.xual instinct was to be found in the movements undertaken by the males at the commencement of the breeding season. Such movements are characterised by a definiteness of purpose, whether they involve a protracted journey of some hundreds of miles or merely embrace a parish or so in extent, and that purpose is the acquirement of a territory suitable for rearing offspring. They are thus directly related to the territory, and the question arises as to whether their origin may not be traced to such relatedness. So long as we fix our attention solely upon the magnitude of the distance traversed the suggestion may seem a fanciful one. Nevertheless, if the battles between males of the same species _are_ directly related to the occupation of a position suitable for breeding purposes, if those which occur between males of closely related forms _can_ be traced to a similar source, if the females take their share in the defence of the ground that is occupied, if, in short, the compet.i.tion is as severe as I believe it to be, and is wholly responsible for the strife which is prevalent at the commencement of the breeding season--then such compet.i.tion must have introduced profound modifications in the distribution of species; it must have even influenced the question of the survival of certain forms and the elimination of others; and since the powers of locomotion of a bird are so highly developed it must have led to an extension of breeding range, limited only by unfavourable conditions of existence.

CHAPTER II

THE DISPOSITION TO SECURE A TERRITORY

Those who have studied bird life throughout the year are aware that the distribution of individuals changes with the changing seasons. During autumn and winter, food is not so plentiful and can only be found in certain places, and so, partly by force of circ.u.mstances and partly on account of the gregarious instinct which then comes into functional activity, different individuals are drawn together and form flocks of greater or less dimensions, which come and go according to the prevailing climatic conditions. But with the advent of spring a change comes over the scene: flocks disperse, family parties break up, summer migrants begin to arrive, and the hedgerows and plantations are suddenly quickened into life. The silence of the winter is broken by an outburst of song from the throats of many different species, and individuals appear in their old haunts and vie with one another in advertising their presence by the aid of whatever vocal powers they happen to possess--the Woodp.e.c.k.e.r utters its monotonous call from the accustomed oak; the Missel-Thrush, perched upon the topmost branches of the elm, persistently repeats its few wild notes; and the Swallow returns to the barn.

All of this we observe each season, and our thoughts probably travel to the delicate piece of architecture in the undergrowth, or to the hole excavated with such skill in the tree trunk; to the beautifully shaped eggs; to the parent birds carrying out their work with devoted zeal--in fact, to the whole series of events which complete the s.e.xual life of the individual; and the attachment of a particular bird to a particular spot is readily accounted for in terms of one or other of the emotions which centre round the human home.

But if this behaviour is to be understood aright; if, that is to say, the exact position it occupies in the drama of bird life is to be properly determined, and its biological significance estimated at its true value, it is above all things necessary to refrain from appealing to any one of the emotions which we are accustomed to a.s.sociate with ourselves, unless our ground for doing so is more than ordinarily secure. I shall try to show that, in the case of many species, the male inherits a disposition to secure a territory; or, inasmuch as the word "secure" carries with it too much prospective meaning, a disposition to remain in a particular place when the appropriate time arrives.

If the part which the breeding territory plays in the s.e.xual life of birds is the important one I believe it to be, it follows that the necessary physiological condition must arise at an early stage in the cycle of events which follow one another in ordered sequence and make towards the goal of reproduction, and that the behaviour to which it leads must be one of the earliest visible manifestations of the seasonal development of the s.e.xual instinct. When does this seasonal development occur? For how long does the instinct lie dormant? In some species there is evidence of this first step in the process of reproduction early in February; there is reason to believe that in others the latter part of January is the period of revival; and the possibility must not be overlooked of still earlier awakenings, marked with little definiteness, though nevertheless of sufficient strength to call into functional activity the primary impulse in the s.e.xual cycle. Here, then, we meet with a difficulty so far as direct observation is concerned, for the duration of the period of dormancy and the precise date of revival vary in different species; and, if accurate information is to be obtained, the study of the series of events which culminate in the attainment of reproduction ought certainly to begin the moment behaviour is influenced by the internal changes, whatever they may be, which are responsible for the awakening of the s.e.xual instinct.

In considering how this difficulty might be met, the importance of migratory species as a channel of information was gradually borne in upon me; for it seemed that the definiteness with which the initial stage in the s.e.xual process was marked off, as a result of the incidence of migration, would go far towards removing much of the obscurity which appeared to surround the earlier stages of the breeding problem in the case of resident species. Recent observation has shown that I exaggerated this difficulty, and that it is generally possible to determine with reasonable accuracy the approximate date at which the internal changes begin to exert an influence on the behaviour of resident species also. Nevertheless, the specialised behaviour of the migrants furnished a clue, and pointed out the direction which further inquiry ought to take.

Those who are accustomed to notice the arrival of the migrants are aware that the woods, thickets, and marshes do not suddenly become occupied by large numbers of individuals, but that the process of "filling up" is a gradual one. An individual appears here, another there; then after a pause there is a further addition, and so on with increasing volume until the tide reaches its maximum, then activity wanes, and the slowly decreasing number of fresh arrivals pa.s.ses unnoticed in the wealth of new life that everywhere forces itself upon our attention. If now, instead of surveying the migrants as a whole, our attention be directed to one species only, this gradual arrival of single individuals in their accustomed haunts will become even more apparent; and if the investigation be pursued still further and these single individuals observed more closely, it will be found that in nearly every case they belong to the male s.e.x. Males therefore arrive before females. This does not mean, however, that the respective times of arrival of the males and females belonging to any one species are definitely divided, for males continue to arrive even after some of the females have reached their destination; and thus a certain amount of overlapping occurs. A truer definition of the order of migration would be as follows:--Some males arrive before others, and some females arrive before others, but on the average males arrive before females. This fact has long been known.

Gatke refers to it in his _Birds of Heligoland_. "Here in Heligoland,"

he says, "the forerunners of the spring migration are invariably old males; a week or two later, solitary old females make their appearance; and after several weeks, both s.e.xes occur mixed, _i.e._, females and younger males; while finally only young birds of the previous year are met with." Newton alludes to it as follows:--"It has been ascertained by repeated observation that in the spring movement of most species of the northern hemisphere, the c.o.c.k birds are always in the van of the advancing army, and that they appear some days, or perhaps weeks, before the hens"; and Dr Eagle Clarke, in his _Studies in Bird Migration_, makes the following statement:--"Another characteristic of the spring is that the males, the more ardent suitors, of most species, travel in advance of the females, and arrive at their meeting quarters some days, it is said in some cases even weeks, before their consorts." Some interesting details were given in _British Birds_[1] in regard to the s.e.x of the migrants that were killed by striking the lantern at the Tuskar Rock, Co. Wexford, on the 30th April 1914. In all, there were twenty-four Whitethroats, nine Willow-Warblers, eight Sedge-Warblers, and six Wheatears; and on dissection it was found that twenty Whitethroats, seven Willow-Warblers, eight Sedge-Warblers, and one Wheatear were males.

What a curious departure this seems from the usual custom in the animal world! Here we have the spectacle afforded us of the males, in whom presumably the s.e.xual instinct has awakened, deserting the females just at the moment when we might reasonably expect their impulse to accompany them would be strongest; and this because of their inherited disposition to reach the breeding grounds. If, in order to attain to reproduction, the male depended primarily upon securing a female--whether by winning or fighting matters not at the moment--if her possession const.i.tuted the sole difference in his external environment between success and failure, then surely one would suppose that an advantage must rest with those individuals which, instead of rushing forward and inflicting upon themselves a life of temporary isolation, remained with the females and increased their opportunities for developing that mutual appreciation which, by some, is held to be a necessary prelude to the completion of the s.e.xual act, and to which close companionship would tend to impart a stimulus.

In thus speaking, however, we a.s.sume that the revival of the s.e.xual instinct in the migratory male is coincident in time with its return to the breeding quarters; and we do so because the act of migrating is believed to be the first step in the breeding process. But it is well to bear in mind just how much of this a.s.sumption is based upon fact, and how much is due to questionable inference. All that can be definitely a.s.serted is this, that appropriate dissection reveals in most of the migrants, upon arrival at their destination, unquestionable evidence of seasonal increase in the size of the s.e.xual organs. Beyond this there is nothing to go upon. Yet if the term "s.e.xual instinct" is held to comprise the whole series of complex relationships which are manifest to us in numerous and specialised modes of behaviour, which ultimately lead to reproduction, and which have gradually become interwoven in the tissue of the race, there can be little doubt that the a.s.sumption is a reasonable one. To some, the term may recall the fierce conflicts which are characteristic of the season; to others, emotional response; to not a few, perhaps, the actual discharge of the s.e.xual function--all of these, it is true, are different aspects of the one instinct; but at the same time each one marks a stage in the process, and the different stages follow one another in ordered sequence. However, we are not concerned at the moment with the term in its wider application; we wish to know the precise stage at which the disposition to mate influences the behaviour of the male. Is the female to him, from the moment the seasonal change in his s.e.xual organs takes place, a goal that at all costs must be attained? Or is it only when the cycle of events which leads up to reproduction is nearing completion that she looms upon his horizon? One would like to be in a position to answer these questions, but there is nothing in the way of experimental evidence to go upon; and if I say that there is reason to believe that, in the earlier stages, the female is but a shadow in the external environment of the male, it must be taken merely as an expression of opinion, though based in some measure upon a general observation of the behaviour of various species.

Before attempting to explain the difference in the times of arrival of the male and female migrant, let us examine the behaviour of some resident species at a corresponding period. My investigations have been made princ.i.p.ally amongst the smaller species--the Finches and the Buntings--which often pa.s.s the winter in or near the localities wherein they brought up offspring or were reared. It is true that they wander from one field to another according to the abundance or scarcity of food; it is also true that, if the weather is of a type which precludes the possibility of finding the necessary food, these wanderings may become extensive or even develop into partial migrations. But under the normal climatic conditions which prevail in many parts of Britain, these smaller resident species seem to find all that they require without travelling any great distance from their breeding haunts. Flocks composed of Yellow Buntings, Cirl Buntings, Corn-Buntings, Chaffinches, Greenfinches, etc., can be observed round the farmsteads or upon arable land; small flocks of Reed-Buntings take up their abode on pieces of waste land and remain there until the supply of food is exhausted, deserting their feeding ground only towards evening when they retire to the nearest reed-bed to pa.s.s the night; flocks of Hawfinches visit the same holly-trees day after day so long as there is an abundance of berries on the ground beneath; and so on.

I have mentioned the Reed-Bunting; let us take it as our first example and try to follow its movements when the influence exerted by the internal secretions begins to be reflected on the course of its behaviour. First, it will be necessary to discover the exact localities in any given district to which the species habitually returns for the purpose of procreation; otherwise the earlier symptoms of any disposition to secure a territory may quite possibly be overlooked in the search for its breeding haunts.

In open weather Reed-Buntings pa.s.s the winter either singly, in twos or threes, or in small flocks, on bare arable ground, upon seed fields, or in the vicinity of water-courses; but in the breeding season they resort to marshy ground where the _Juncus communis_ grows in abundance, to the dense ma.s.ses of the common reed (_Arundo phragmites_), and such like places. During the winter, the male's routine of existence is of a somewhat monotonous order, limited to the necessary search for food during the few short hours of daylight and enforced inactivity during the longer hours of darkness. But towards the middle of February a distinct change manifests itself in the bird's behaviour. Observe what then happens. When they leave the reed-bed in the morning, instead of flying with their companions to the accustomed feeding grounds, the males isolate themselves and scatter in different directions. The purpose of their behaviour is not, however, to find fresh feeding grounds, nor even to search for food as they have been wont to do, but rather to discover stations suitable for the purpose of breeding; and, having done so, each male behaves in a like manner--it selects some willow, alder, or prominent reed, and, perching thereon, leads a quiet life, singing or preening its feathers. Now if the movements of one particular male are kept in view, it will be noticed that only part of its time is spent in its territory. At intervals it disappears. I do not mean that one merely loses sight of it, but that it actually deserts its territory. As if seized with a sudden impulse it rises into the air and flies away, often for a considerable distance and often in the same direction, and is absent for a period which may vary in length from a few minutes to an hour or even more. But these periodical desertions become progressively less and less frequent in occurrence until the whole of its life is spent in the few acres in which it has established itself.

The behaviour of the Yellow Bunting is similar. In any roadside hedge two or more males can generally be found within a short distance of one another, and in such a place their movements can be closely and conveniently followed. Under normal conditions the ordinary winter routine continues until early in February; but the male then deserts the flock, seeks a position of its own, and becomes isolated from its companions. Now the position which it selects does not, as a rule, embrace a very large area--a few acres perhaps at the most. But there is always some one point which is singled out and resorted to with marked frequency--a tree, a bush, a gate-post, a railing, anything in fact which can form a convenient perch, and eventually it becomes a central part of the bird's environment. Here it spends the greater part of its time, here it utters its song persistently, and here it keeps watch upon intruders. The process of establishment is nevertheless a gradual one.