The conflicts between males that are definitely paired are of such common occurrence that it is scarcely necessary to mention specific instances. But the occasions on which a male attacks either s.e.x of a neighbouring pair indiscriminately, or on which a pair combine to attack a female, are less frequent.

Now if it be true that males fight for no other purpose than to gain possession of a mate, what meaning are we to attach to the battles between the pairs, or what explanation are we to give of the fact that paired males are so frequently hostile? Those who hold this view will probably argue thus: "The presence of the female is the condition under which the pugnacious instinct of the male is rendered susceptible to appropriate stimulation, and the stimulus is supplied by a rival male; we admit that all the fighting which occurs after pairing has taken place has nothing to do strictly speaking with gaining a mate, but, inasmuch as the fact of possession is always liable to be challenged--and no male can differentiate between a paired and an unpaired intruder--we contend that it would add to the security of possession if the pugnacious instinct remained susceptible to stimulation so long as there were any possibility of challenge from an unpaired male; and we think that the waste of energy involved in the struggles between paired birds, and which we grant is purposeless, would be more than balanced by the added security." This is a possible explanation and requires consideration. It cannot account for all the diverse ways in which the s.e.xes are mixed up in the fighting--it cannot, for instance, explain the fact that an unpaired male will attack either s.e.x of an adjoining pair indiscriminately--but nevertheless it appears at first sight to be a reasonable explanation of some of them. We must remember, however, that fighting continues throughout the whole period of reproduction. Even after the discharge of the s.e.xual function has ceased, and the female is engaged in incubation or in tending her young, the male is still intolerant of intruders; and it is difficult to believe that, at so late a stage in the process, a female could be any attraction s.e.xually to an unpaired male. But apart from any theoretical objection, there remains the fact--namely that there is no evidence that a male, after having once paired, is liable to be robbed of its mate. And in support of this fact I have only to state that I have met with no single instance of failure to obtain and hold a mate when once a territory had been secured. Bearing in mind then that both s.e.xes partic.i.p.ate in the fighting, and that individuals of the opposite s.e.x frequently attack one another; that all such conflicts are characterised by persistent effort, and that they are not limited to just the particular period when the s.e.xual instinct is dominant but continue throughout the breeding season; bearing in mind that in at least one form of this promiscuous warfare the influence of the female can be definitely excluded, and that, in the remaining forms, the evidence which is required to link them up with the biological end of securing mates is lacking--can it be denied that the complexity of the strife makes against the view that the possession of a female is the proximate end for which the males are fighting?

We started with the most simple aspect of the whole problem, the fighting of two males in the presence of one female--the aspect upon which attention has usually been fixed. And if it remained at that, if observation failed to disclose any further development in the situation, then there would be no need to probe the matter deeper, there would be no reason to doubt the a.s.sertion that the quarrel had direct reference to the female. But a.s.suredly no one can ponder over the diversity of battle and still believe that the possession of a mate furnishes an adequate solution of the mystery. Clearly such an hypothesis cannot cover all the known facts; there are conflicts between separate pairs, and there are conflicts between males when females are known to be absent and when their mates are even engaged in the work of incubation--these cannot be due to an impulse in a member of one s.e.x to gain or keep possession of one of the other s.e.x. So that taking all these facts into consideration, we are justified, I think, in hesitating to accept this view, and must look elsewhere for the real condition under which the pugnacious nature of the male is rendered susceptible to appropriate stimulation.

What then is the meaning of all this warfare? The process of reproduction is a complex one, built up of a number of different parts forming one inter-related whole; it is not merely a question of "battle," or of "territory," or of "song," or of "emotional manifestation," but of all these together. The fighting is thus one link in a chain of events whose end is the attainment of reproduction; it is a relationship in an inter-related process, and to speak of it as being even directly related to the territory is scarcely sufficient, for it is intimately a.s.sociated with the disposition which is manifested in the isolation of the male from its companions, and forms therewith an _imperium in imperio_ from which our concept of breeding territory is taken. But let me say at once that it is no easy matter to prove this, for since so many modes of behaviour, which can be interpreted as lending support to this view, are likewise interpretable on the view that the presence of a female is a necessary condition of the fighting, it is difficult to find just the sort of evidence that is required.

Nevertheless, after hearing the whole of the evidence and at the same time keeping in mind the conclusion which we have already reached, I venture to think that the close relationship between the warfare on the one hand and the territory on the other will be fully admitted.

Formerly I deemed the spring rivalry to be the result of accidental encounters, and I believed that an issue to a struggle was only reached when one of the combatants succ.u.mbed or disappeared from the locality, a view which neither recognised method nor admitted control. Recent experience has shown, however, that I was wrong, and that there is a very definite control over and above that which is supplied by the physical capabilities of the birds.

Let us take some common species, the Willow-Warbler being our first example; and, having found three adjoining territories occupied by unpaired males, let us study the conflicts at each stage in the s.e.xual life of the three individuals, observing them before females have arrived upon the scene, again when one or two of the three males have secured mates, and yet again when all three have paired. Now we shall find that the conditions which lead up to and which terminate the conflicts are remarkably alike at each of these periods. A male intrudes, and the intrusion evokes an immediate display of irritation on the part of the owner of the territory, who, rapidly uttering its song and jerking its wings, begins hostilities. Flying towards the intruder, it attacks viciously, and there follows much fluttering of wings and snapping or clicking of bills. At one moment the birds are in the tree-tops, at another in the air, and sometimes even on the ground, and fighting thus they gradually approach and pa.s.s beyond the limits of the territory. Whereupon a change comes over the scene; the male whose territory was intruded upon and who all along had displayed such animosity, betrays no further interest in the conflict--it ceases to attack, searches around for food, or sings, and slowly makes its way back towards the centre of the territory.

Scenes of this kind are of almost daily occurrence wherever a species is so common, or the environment to which it is adapted so limited in extent, that males are obliged to occupy adjacent ground. The Moor-Hen abounds on all suitable sheets of water, and it is a bird that can be conveniently studied because, as a rule, there is nothing, except the rushes that fringe the pool, to hinder us from obtaining a panoramic view of the whole proceedings, and moreover the area occupied by each individual is comparatively small. Towards the middle of February, symptoms of s.e.xual organic change make themselves apparent, and the pool is then no longer the resort of a peaceable community; quarrels become frequent, and as different portions of the surface of the water are gradually appropriated, so the fighting becomes more incessant and more severe. Each individual has its own particular territory, embracing a piece of open water as well as a part of the rush-covered fringe, within which it moves and lives. But in the early part of the season, when the territories are still in process of being established, and definiteness has still to be acquired, trespa.s.sing is of frequent occurrence, and the conflicts are often conspicuous for their severity.

Now these conflicts are not confined to unpaired individuals, nor to one s.e.x, nor to one member of a pair--every individual that has settled upon the pool for the purpose of breeding will at one time or another be involved in a struggle with its neighbour. If then we single out certain pairs and day by day observe their actions and their att.i.tude towards intruders, we shall notice that, instead of their routine of existence consisting, as a casual acquaintance with the pool and its inmates might lead us to believe, of an endless series of meaningless disputes, the behaviour of each individual is directed towards a similar goal--the increasing of the security of its possession; and further, if we pay particular attention to the circ.u.mstances which lead up to the quarrels and the circ.u.mstances under which such quarrels come to an end, we shall find, when we have acc.u.mulated a sufficient body of observations, that the disputes always originate in trespa.s.s, and that hostilities always cease when the trespa.s.ser returns again to its own territory. By careful observation it is possible to make oneself acquainted with the boundaries--I know not what other term to use--which separate this territory from that; and it is the conduct of the birds on or near these boundaries to which attention must be drawn. A bird may be feeding quietly in one corner of its territory when an intruder enters. Becoming aware of what is happening it ceases to search for food, and approaching the intruder, at first swimming slowly but gradually increasing its pace, it finally rises and attacks with wings and beak, and drives its rival back again beyond the boundary. Thereupon its att.i.tude undergoes a remarkable change; ceasing to attack, but remaining standing for a few moments as if still keeping guard, it betrays no further interest in the bird with which a few seconds previously it was fighting furiously. On one occasion I watched a trespa.s.ser settle upon a conspicuous clump of rushes situated near the boundary. The owner, who was at the moment some distance away, approached in the usual manner, and, having driven off the trespa.s.ser, returned immediately to the clump, where it remained erect and motionless.

A feature which marks all the fighting, and which we cannot afford to disregard, is the conative aspect of the behaviour of the owner of the territory. The bird attacks with apparent deliberation _as if_ it were striving to attain some definite end. I recollect an incident which was interesting from this point of view. A pair of Reed-Buntings were disturbed by a Weasel which had approached their nest containing young.

Both birds betrayed symptoms of excitement; as the Weasel threaded its way amongst the rushes, so they fluttered from clump to clump or clung to the stems, uttering a note which is peculiar to times of distress, and followed it thus until finally it disappeared in a hedge. The rapidly uttered note and the excitement of the birds caused some commotion, and the male from an adjoining territory approached the scene. Now one would have expected that the presence of this bird, and possibly its aid in driving away a common enemy, would have been welcomed; one would have thought that all else would have been subservient to the common danger, and that so real a menace to the offspring would have evoked an impulse in the parent powerful enough to dominate the situation and subordinate all the activities of the bird to the attainment of its end. But what happened? Three times during this incident, the male, whose young were in danger, abandoned the pursuit of the Weasel and pursued the intruder. It was not merely that he objected to the presence of this neighbouring male in a pa.s.sive way, nor even that he had a momentary skirmish with it, but that he determinedly drove the intruder beyond the boundary and only then returned to hara.s.s the Weasel.

Thus it seems clear that the proximate end to which the fighting is directed is not necessarily the defeat of the intruder, but its removal from a certain position. And inasmuch as this result will be obtained whether the retreat is brought about by fear of an opponent or by physical exhaustion, it is manifest that too much significance need not be attached to the amount of injury inflicted. It is necessary to bear this in mind, because it is held by some, who have carefully observed the actions of various species, that overmuch importance is attached to the conflicts, that in a large number of instances they are mere "bickerings" and lead to nothing, and that they are now only "formal,"

which means, I suppose, that they are vestigial--fragments of warfare that determined the survival of the species in bygone ages. But if the conclusion at which we have just arrived be correct, if we can recognise a single aim pa.s.sing through the whole of the warfare--and that one the removal of an intruder from a certain position, then we need no longer concern ourselves as to the degree of severity of the battles--we see it all in true perspective. Neither exhaustion nor physical inability are the sole factors which determine the nature and extent of the fighting; there is a more important factor still--position. According, that is to say, to the position which a bird occupies whilst fighting is in progress, so its pugnacious nature gains or loses susceptibility, and it is this gain or loss of susceptibility which I refer to when I speak of the fighting as being controlled.

What we have then to consider is the relation of "susceptibility" to "position." We can explain the relationship in two ways. We can say that the part of the nature of the male which leads to the occupation of a territory, and is partly hereditary and partly acquired, is stronger than the part which leads the bird to fight, and which is conditioned by the presence of a female, and that consequently when the male pa.s.ses the boundary, the impulse to return a.s.serts itself and the conflict ceases; or we can say that the occupation of a territory is the condition under which the pugnacious instinct is rendered susceptible to stimulation, that the stimulus is supplied by the intruder, and that when the male pa.s.ses outside the accustomed area its instinct is no longer so susceptible and it therefore retires from the conflict.

[Ill.u.s.tration: Long-tailed t.i.t Males fighting for possession of territory. The feathers have been torn from the crown of the defeated and dying rival.

Emery Walker ph.sc.]

Of these explanations, the first is not altogether satisfactory. It requires the presence of a female and, as we have seen, a female is by no means always present. Then it attributes to the one side of the inherited nature an influence which is not borne out by the facts, for in the ordinary routine of existence, without the incentive of battle, every individual is liable to wander occasionally beyond its boundary and to intrude temporarily upon its neighbours; and this it could scarcely do, providing its nature to remain within the territory were powerful enough to dominate its movements and curtail its activities even during the excitement of an encounter. But there is nothing inherently improbable in the alternative hypothesis, nor anything that is at all inconsistent with the behaviour as observed; on the contrary, if it is admitted, the facts become connected together and exhibit a meaning which they otherwise would not have possessed.

So much for the controlling influence of "position," which alone seems to me sufficient ground for believing that the fighting has reference to the territory. But it is not the whole of the evidence.

Now if it were possible to demonstrate by actual observation that those males which had not established territories were not pugnacious, we should have something in the nature of proof of the correctness of this view. Demonstrative evidence of this kind is, however, unattainable. Yet we can come very near to obtaining it by reason of a peculiar feature which marks the process of acquiring territory--the neutral ground. The Lapwing will serve as an ill.u.s.tration. In the previous chapter I referred to the small flocks that appeared in the accustomed water meadow early in February, and I described how they settled day after day in that meadow, but only in a limited part of it, where they pa.s.sed their time in rest, in preening their feathers, or in running this way and that lazily searching for food; and how, at length, the flock dwindled by reason of individuals breaking away in order to secure positions on the remaining part of the meadow. Here the neutral ground is adjacent to the territories, and, while still occupied by the flock, is resorted to by the males that had deserted that flock in order to establish those territories.

Suppose now that we have the whole meadow in view from some point of vantage. In front of us are the territories, in the distance the neutral ground; and in each territory there is a solitary male, while on the neutral ground a number of individuals of both s.e.xes are a.s.sembled, and move about freely one amongst another. So that the scene presented to view is somewhat as follows: a flat meadow, at one end of which, and at fairly regular intervals, a few solitary individuals are dotted about, each one keeping at a distance from its neighbours; while at the other end a number of individuals are collected together in a comparatively small s.p.a.ce, apparently deriving some satisfaction from their close a.s.sociation. That surely is a very remarkable contrast. But let us continue our investigation, first fixing our attention upon the solitary individuals; one is standing preening its feathers, another is squatting upon the ground, a third runs a few yards in this direction then a few yards in that, stimulated apparently by the sight of food, and so on.

Moreover, each one keeps strictly to a well-defined area and makes no attempt to a.s.sociate with its fellows. One of the males, however, whilst roaming backwards and forwards approaches the limit of its territory, and this brings the neighbouring bird, whose boundary is threatened, rapidly to the spot. In an upright position both stand face to face, and the battle then begins; with their wings they attempt to beat one another about the body, with their beaks they aim blows at the head, and in the melee wings and legs seem to be inextricably mixed; whilst at intervals, driven backwards by the force of the collision, they are compelled to separate, only, however, to return to the charge--and the sound of beating wings and the feathers that float in the air are tokens of earnestness. Such scenes are of frequent occurrence; but the conflicts vary in intensity, and the circ.u.mstances under which they occur vary too, and females come and go without leaving any clue as to their ultimate intentions.

Turning now to the flock one is impressed with the friendship that seems to exist between the various members. There are, it is true, occasional displays of pugnacity which never seem to develop into anything very serious; for instance, one bird will fly at another, and a momentary scuffle is followed by a short pursuit but nothing more--nothing, that is to say, in the least comparable with the battle previously described.

Of what is the flock composed? Of members of both s.e.xes. There is no difficulty in a.s.suring oneself that this is so. But is it entirely composed of individuals in whom development has not reached a stage adequate for the functioning of the primary dispositions? No, not entirely; for it will be observed that its number is a fluctuating one, that birds come and go, and, if a close watch is kept upon the different individuals as they leave, it will be noticed that some at least are inmates of the territories at the opposite end of the meadow--the solitary members whose behaviour we were recently watching. This fact is an important one. We were impressed, it may be remembered, with the contrast between the general behaviour of the birds at the opposite ends of the meadow. But now it appears as if the contrast were not between this individual and that, but between the behaviour of the same one under different circ.u.mstances. The male, that is to say, which, while in its territory, tolerates the approach of no other male, flies to the flock and is there welcomed by the very individuals with whom a short time previously it had been engaged in serious conflict.

But if the conditions are reversed and the flock happens to settle in an occupied territory, the att.i.tude of the owner towards the flock is very different. In the year 1916 an incident of this kind occurred in the meadow to which reference has already been made. The weather had been exceptionally severe--very cold easterly and north-easterly winds, frost, and frequent falls of snow had affected the behaviour of the Lapwings, and seemed to have checked the normal development of their s.e.xual routine. The males would attempt to establish themselves, and then, when the temperature fell and the ground was covered with snow, would collect again in flocks and follow their winter routine. It was on the 9th March, during one of the spells of milder weather, that the flock on the neutral ground was disturbed and settled mainly in the territory marked No. 3 on the 1916 plan, but partly on that marked No.

2. The owners thereupon began to attack the different members of the invading flock. Fixing attention upon a particular bird whilst ignoring the remainder, the No. 3 male drove it away, and then after a pause drove another away, and so on until by degrees all the invaders were banished, and the No. 2 male did likewise. The interest of this incident lies, however, in the behaviour of the different individuals of which the flock was composed; when attacked they made no real show of resistance, but accepted the situation and left. The will to fight was clearly lacking, yet their presence was a source of annoyance to the owners of the territories. A short time previously a female had accompanied one of the males and was at that time somewhere in the vicinity, but beyond this there was no evidence to show that either of them were paired, and even if the presence of the female were the reason of the pugnacity of the one, it could not well account for that of the other.

The neutral ground does not always happen to be so close at hand as in the case of the meadow referred to. Sometimes the birds will resort to a particular field, attracted probably by a plentiful supply of food, and here they collect and behave as they do during the winter, running this way and that as the fancy takes them, meeting together by accident at one moment, parting at another, according to the direction in which they happen to wander. Of animosity there is little sign; the season might be the middle of winter instead of the middle of March for all the indication there is of s.e.xual development, and yet one knows that they will behave differently when they leave this ground, as presently they will, and return to their territories in the surrounding neighbourhood, and that there each one will fight if necessary to preserve its acre from intrusion.

It would seem, then, from this that the fighting must bear some relation to the particular area of ground in which it occurs; and unless it can be shown that there is some other factor in the external environment of the male, that is the direction in which we must look for the condition under which the instinct is rendered susceptible. One's thoughts turn, of course, to the female, but she too pa.s.ses backwards and forwards between the territories and the neutral ground, and if her presence were really a _conditio sine qua non_ of the strife, one would like to know why, when she leaves those territories and joins the flock and the males do likewise, similar conflicts should not prevail there also.

Other species have their neutral ground, but the environment seldom affords such facilities for observation as does that of the Lapwing.

Even though the Moor-Hens, who are so conspicuously intolerant upon the pool, _do_ feed together amicably upon the meadows adjoining; and the Chaffinch that is so pugnacious in the morning, _does_ seek out the flock later in the day; yet their conditions of existence prevent our obtaining a panoramic view of the whole proceeding, and we have to study each scene separately before discovering that the relationship between intolerance and the territory on the one hand, and friendship and the neutral ground on the other, is just as strong a feature as it is in the behaviour of the Lapwing.

I shall now give a brief account of the conduct of a male Reed-Bunting which by persistent effort established itself late in the season, and I shall do so because its behaviour tends to confirm much that has been said in the preceding pages.

Early in March three male Reed-Buntings occupied a small water meadow overgrown with the common rush, and by the third week all of them were paired. On the 30th March two of the males were unusually pugnacious, and on the following day fighting continued and at times was very severe. Now I knew that the occupants of the ground in which the fighting was taking place were paired, and not doubting that the combatants were the owners of two territories marked for convenience sake Nos. 1 and 2, I was at a loss to understand the meaning of so determined and persistent a struggle. My attention, however, was presently drawn to a third bird, which also joined in the conflict and made the whole situation still more perplexing. This bird, as it soon became clear, was none other than the owner of No. 2 territory, and the one that I had previously regarded as such was a new arrival. On the following day, the 1st April, fighting continued, and in my record for that day there is a note to the effect that "No. 2 female seems to be of no interest to No. 5 male (the new arrival); its purpose seems to be to drive away intruders." On the 2nd April and subsequent days, this bird attacked every other male that approached, and not only maintained its position but ultimately succeeded in securing a mate. Here then we have two territories occupied by two males, both of which had obtained a mate. The relation of these two birds was normal, a month's routine had defined their boundaries, and conflicts were less frequent than formerly. But upon this comparatively peaceful scene a strange male intrudes. Observe the manner of the intrusion. The stranger does not wander about first in this direction and then in that, but acts _as if_ it had some definite end in view, and establishing itself in a small alder bush which it uses as a base or headquarters, it gradually extends its dominion, gains the mastery over the surrounding ground, part of which belonged to No. 1 male and part to No. 2, and finally drives a wedge, so to speak, between the two territories.

How is its behaviour to be explained, and why did its presence cause such commotion? No one could have watched the gradual unfolding of this incident day by day and not have been impressed by the persistent endeavour with which this male maintained its position in one small part of the meadow. This is the first and most important consideration. Then there is the att.i.tude, also significant, which it adopted towards the females; for I take it that, apart from the question of territory, the explanation of its intrusion must be sought in the necessity for securing a mate--that it was attracted by the presence of the females, and that the proximate end of its behaviour was the possession of one of them. But if there is one thing that emerges from the facts more clearly than another it is that the course of its behaviour was in no way influenced by the presence or absence of either of the females. My reasons for saying so are the following: in the first place, it made no attempt to pursue or to thrust its attention upon either one or the other of them; secondly, it even went so far as to attack and drive them away when they approached too closely; and in the third place, when an unpaired female did at length appear, it adopted a different att.i.tude and forthwith paired. And bearing in mind that these two females had already been with their respective mates for some considerable time, and that there was reason to believe that coition had actually taken place, is it likely that any counter-attraction would have proved successful in tempting either of them away from its mate, or probable, if they were the sole attraction, that the intruding male would have been so persistent in remaining? How very much simpler it is to fit the pieces together, if for the time being we ignore the female and fix our attention upon the territory. Each item of behaviour then falls into its proper place, and the fighting which seemed so perplexing and meaningless becomes a factor of prime importance. First of all the male arrives; then it establishes itself in a small alder bush and advertises its presence by song; next, by persistent effort in attacking the neighbouring males, it frees a piece of ground from their dominion; and finally, in proper sequence, a female arrives, pairing takes place, and reproduction is secured.

[Ill.u.s.tration: A battle between two pairs of Jays

Emery Walker ph.sc.]

How then does the whole matter stand? If it were males only that engaged in serious conflict, and if they fought only in the presence of a female, the problem would resolve itself into one simply of obtaining mates. But the warfare extends in a variety of directions, it is not confined to one s.e.x, nor to unpaired individuals, nor need the opponents necessarily be of the same s.e.x; it involves both s.e.xes alike singly or combined. Now the view that the biological end of battle is, in its primary aspect, related to the female, cannot, as we have seen, apply to the conflicts between different pairs, and only by much stretching of the imagination can it be held responsible for the hostility that males frequently display towards females or _vice versa_. It is valid only for a certain form of warfare. But that form represents, you will say, a large proportion of the whole, which is true; and so long as we ignore the remainder, we might rest content in the belief that we had solved the major part of the problem. But can we ignore the remainder? Can we say that the conflicts between paired males, for example, are simply offshoots of the pugnacious disposition, and have no part to play in the process of reproduction? They recur with marked persistency season after season and generation after generation; they are to be found in species widely remote; they are frequent in occurrence; and no one who had observed them and noted the vigour with which they are conducted, could, I think, conclude that they were meaningless--and be satisfied. They must somehow be explained. So that if anyone thinks fit to maintain that possession of a mate is an adequate explanation of part of the hostilities, it is clearly impossible to regard all the fighting as a manifestation of one principle directed towards a common biological end.

But wherever we extend our researches, we find that the facts give precision to the view that the occupation of a territory is the condition under which the pugnacious instinct is rendered susceptible to stimulation. The Lapwing, when in its territory, displays hostility towards other males of its own species, but when upon neutral ground, treats them with indifference; the Chiffchaff pursues its rival up to the boundary and is then apparently satisfied that its object has been achieved; the c.o.c.k Chaffinch in March permits no other male to intrude upon its acre or so of ground during the early hours of the morning, but for the rest of the day it joins the flock and is sociable; the Herring-Gull resents the approach of strangers so long as it occupies its few square feet of cliff, but welcomes companions whilst it is following the plough--all of which points to a relation between the territory and the fighting. And this view has at least one merit--it accounts for all the fighting no matter what degree of severity may be reached or in what way the s.e.xes may be involved. The complexity of the strife presents no obstacle; for if the biological end of the fighting is to render the territory, which has already been established, secure from intrusion, each s.e.x will have its allotted part to play at the allotted time: thus the battles between the males before females appear on the scene will decide the initial question of ownership; those between the females will give an advantage to the more virile members and insure an even distribution of mates for the successful males; the constant struggles between paired males will roughly maintain the boundaries and prevent such encroachment as might hamper the supply of food for the young; and the co-operation of male and female in defence of the territory will be an additional safeguard. Each form of battle will contribute some share towards the main biological function of reproduction.

Hitherto we have dealt princ.i.p.ally with the male. We have referred, it is true, to the fact that the female co-operates with her mate in order to drive away intruders, but beyond this, we have made no attempt to trace what part, if any, she plays in the whole scheme. We must do so now.

The various steps by which the territory is not only established but made secure from invasion, imply an inherited nature nicely balanced in many directions--first of all the male must be so attuned as to be ready to search for a territory at the right moment; then it must be capable of selecting a suitable environment; and, having established itself, it must be prepared to defend its area from a rival, and to resist encroachment by its neighbours--and if it failed in any one of these respects, it would run the risk of failure in the attainment of reproduction. Each individual has therefore to pa.s.s, so to speak, through a number of sieves--the meshes of which are none too wide--before it can have a reasonable prospect of success. This being so, we ask, in the first place, whether the female, too, may not have an eliminating test to pa.s.s; and in the second place, whether she may not also a.s.sist in furthering the biological end of securing the territory.

Now the answer to the first of these questions will be found to be in the affirmative. Just as, in the securing of a territory, the ultimate appeal is to the physical strength of the male, so, in the course of her search for a mate, the female may be called upon to challenge, or may be challenged by a rival, and the issue is decided by force. My attention was first drawn to this fact by a struggle between two female Whitethroats, which I have described elsewhere. The scene of its occurrence was the corner of a small osier bed occupied by one male, and the females that took part in it had only recently arrived, but the male, an unpaired bird, had been in possession of its territory for some days. The sequel to this struggle, which was protracted and severe, was the disappearance of both females, the male being left without a mate for a further ten days.

[Ill.u.s.tration: Emery Walker ph.sc.

The female Chaffinch shares in the defence of the territory and attacks other females.]

Numerous instances have since come under my notice. Hen Chaffinches become so absorbed that they fall to the ground and there continue the struggle. Seizing hold of one another by the feathers of the head, they roll from side to side, and then, without relaxing their grip, lie exhausted--the quickened heart-beat, altered respiration, tightly compressed feathers and partially expanded wings betraying the intensity of the conflict.

As the breeding season approaches, hen Blackbirds grow more pugnacious.

Individuals that early in the year have frequented the same spot daily and have even shown every sign of friendship, become openly hostile. For two years in succession I had an opportunity of observing females under such conditions, and of studying the gradual change in their relationship. Each morning at break of day and for some hours afterwards they could be seen in the same place, one following the other as they searched for food first in this direction and then in that, as if they derived some special pleasure from the fact of their companionship. Then a change began to manifest itself. Indications of animosity became apparent; one would run towards the other in a threatening att.i.tude and, in a half-hearted manner, peck at it; and gradually the hostility grew, until the tentative pecking developed into a scuffle and the scuffle into a conflict.

Much fighting also occurs between the females of the Reed-Bunting, and likewise between those of the Moor-Hen, and because these two species are not only common but inhabit respectively open stretches of marshy ground or large sheets of water, the fighting can be readily observed.

Why do the females fight before they are definitely paired? To obtain mates? This certainly seems to be the obvious explanation because any question of securing territory can be excluded; yet if it be true that their s.e.x is numerically inferior, it is difficult to understand the necessity for such strenuous compet.i.tion. But what is the condition under which the pugnacious instinct of the female is rendered susceptible to stimulation? It cannot be merely the presence of a male ready to breed, for then there would be endless commotion amongst the flocks of Chaffinches or of Lapwings which in March are composed of both s.e.xes, including even males that have secured territories. There must be some other circ.u.mstance; and, judging by experience, it is to be found in the territory--a male, that is to say, in occupation of one, is the condition under which the inherited nature of the female is allowed free play. We must bear in mind, however, that the compet.i.tion between the males is very severe, that large numbers probably fail to pa.s.s even this preliminary test, and that only a proportion are in a position to offer to the female the condition under which her process can successfully run its course; so that the presumption is--though it is incapable of demonstration--that there is a compet.i.tion for such males each recurring season, and that, on the average, the weaker females fail to procreate their kind.

But apart from any direct a.s.sistance she may give in driving away intruders, does she in any way help to further the biological end of reproduction? This is a difficult question to answer, and the suggestion I have to make can only apply in those cases in which the territory is occupied throughout the breeding season. Much of the fighting between the males occurs in her presence, and it must be admitted--though it is difficult to speak with any degree of certainty--that such fighting, taken as a whole, bears the stamp of exceptional determination. Let us then grant that the excitement of a male does, under these circ.u.mstances, reach a higher level of intensity, and let us see how this will add to the security of the territory. The fact that the male has established itself and obtained a mate is not alone sufficient to accomplish the end for which the territory has been evolved. During the period between the initial discharge of the s.e.xual function and the time when incubation draws to a close, much may happen to prejudice the future of the offspring; there is always the possibility of invasion by an individual whose development is backward or which has been unsuccessful in making good the first step, and, as we saw in the case of the Reed-Bunting, a portion of the ground won may be lost; there is always the danger of gradual encroachment by neighbouring owners; and there is even a possibility that a pair may be so persistently hara.s.sed by more virile neighbours as to forsake the locality permanently. If then a male is to attain a full measure of success it must be capable of keeping its boundaries intact up to the time when the young are able to fend for themselves, and consequently it is important that its intolerant nature should remain susceptible to stimulation throughout the greater part of the season.

Does the presence of a female serve to promote this end? Now we know very little of the influence exerted by one s.e.x upon the other.

Professor Lloyd Morgan has suggested that the male raises the emotional tone of the female, a suggestion which seems to me in accordance with the facts. There is reason to believe, however, that the converse is also true--namely that the excitement of the male reaches a higher level of intensity when a female is present. Granting then that his emotional tone is raised, how will this affect the question? So great is the difference of opinion as to the part that the emotions play in furthering the life of the individual that one hesitates to accept any particular one. But it seems to be generally admitted that emotion adds to the efficacy of behaviour, and this is the view of Professor Lloyd Morgan. "Whatever may be the exact psychological nature of the emotions, it may be regarded," he says, "as certain that they introduce into the conscious situation elements which contribute not a little to the energy of behaviour. They are important conditions to vigorous and sustained conation." Therefore, if it be true that the female raises the emotional tone of the male, the result will be an increased flow of energy into all the specific modes of behaviour connected with reproduction, amongst which those directly concerned in the securing and defence of the territory will receive their share; so that instead of a progressive weakening of just those elements in the situation which make for success, the level of their efficiency will be maintained as a result of such reinforcement. But the female becomes intolerant of her own s.e.x when she has discovered a male ready to breed, and, later, a.s.sists her mate in resisting intrusion; and by raising her emotional tone, he may be the means of furthering more strenuous behaviour on her part. Each member of the pair would in this way contribute towards the energy of behaviour of its mate, and hence add indirectly to the security of the territory.

It may be well to ill.u.s.trate the foregoing remarks. Suppose that there is a small piece of woodland barely sufficient to hold three pairs of Willow-Warblers, and suppose that the male and female in the middle territory did not respond to one another's influence quite as readily as the adjoining males and females, what would be the result? The emotional tone of the central pair would stand at a lower level of intensity; and, since their congenital dispositions would lack the necessary reinforcement, the birds would tend to become less and less punctilious in keeping their boundaries intact, whereas the adjoining pairs, always on the alert and meeting with little opposition, would encroach more and more and gradually extend their dominion. And so, by the time the young were hatched, the parents would be in occupation of an area too limited in extent to insure the necessarily rapid supply of food, and would be compelled to intrude upon the adjoining ground. But knowing how routine becomes ingrained in the life of the individual, knowing that for weeks this pair had submitted to their neighbours, can we believe that they would be capable of a.s.serting their authority and that the young would be properly cared for? Or suppose that different pairs of Kittiwake Gulls on the crowded ledges, or different pairs of Puffins in the crowded burrows, varied in like manner, would they all have equal chances of rearing their offspring? The struggle for reproduction is nowhere more severe than amongst the cliff-breeding sea birds; it is not for nothing that one sees Kittiwake Gulls, locked together, fall into the water hundreds of feet below and struggle to the point of exhaustion, or, as has been reported, to the point of death; it is not for nothing that Puffins fight with such desperation. And surely success will be attained by that pair whose emotional tone stands high and whose impulse to fight is therefore strong, rather than to the ill-a.s.sorted couple.

The argument, then, is briefly this. In the spring, a marked change takes place in the character of the males of very many species; instead of being gregarious they either avoid one another and become hostile, or, if their conditions of existence require that they shall still live together, they become irritable and pugnacious. This change is made known to us by the battles of varying degrees of severity which are such a feature of bird life in the spring; and since a female can commonly be observed to accompany the combatants, the possession of a mate appears at first sight to be the proximate end for which the males are contending. But when the circ.u.mstances which lead up to the quarrels are investigated closely, the problem becomes more difficult; for it is not merely a question of males fighting in the presence of a female, as is generally supposed to be the case, but on the contrary there is a complexity of strife which is bewildering--males attack females or _vice versa_; female fights with female; or a pair combine to drive away another pair, or even a solitary individual no matter of which s.e.x. This complexity of strife makes against the view that the possession of a mate is the reason of the fighting. But an even stronger objection is to be found in the fact that males are hostile when no female is present--and hence we must seek elsewhere for the true explanation.

Now if the behaviour of a male be closely observed, it will be found that its pugnacious instinct gains or loses susceptibility according to the position which it happens to occupy--when its ground is trespa.s.sed upon, the impulse to fight is strong; but when it crosses the boundary it seems to lose all interest in the intruder. Moreover, in some species, the male rejoins the flock at intervals during the early part of the season and for a time leads a double existence, pa.s.sing backwards and forwards between its territory and the neutral ground. Its behaviour under these circ.u.mstances affords some valuable evidence, for the bird displays little if any hostility when accompanying the flock, yet when it returns to the ground over which it exercises dominion, no male can approach without being attacked. The conclusion, therefore, seems to be inevitable, namely that the actual occupation of a territory is the condition under which the pugnacious nature of the male is rendered susceptible to appropriate stimulation.