a pr 2 ¥ 7 a ms, aur pb aor) Pi en \ Nearer ee ie Ah ieee u } i Ee hare ie “ A at Meany uy 1 on i P s ‘ i ¢ mY: ™ pat rf | Lad } f] ay ; are Yea ch i ee Delt ant iH 3 at - ) 7" a ©. a ? Rick ger ve Me, rs aT if L y 5 a ‘ cf | | a aes a rs, od kel aii Apt ‘1 y f i 8 eo eee ht. || y : ri o a . 3 . 3 i 4 ne “., - : & 0 Fi Nad ids | ‘a iY 8 , _) aan tb ver e - ; Py 7 » 7 Ly ‘) » "? i 7 ee. Ww J say i 7 “eg bed en - ms nie 5 f 7 | rr 1 7 it a a y ae : - ‘a z j o | * ' TERRITORY IN BIRD LIFE f ; } OAL ~ OC) Pott PPCM l S Op PQ LA 1 C4 iE r LAL 4. ( Ca 2 y, f 7 a, TERRITORY IN Rie) B I R D LI (Oe BY H. ELIOT HOWARD WITH ILLUSTRATIONS BY G. E. LODGE AND H. GRONVOLD 2161974 NEW YORK E. P. DUTTON AND COMPANY 1920 Tie | Ae EY nok LF fi : e pty 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 in- vestigation, 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 be- haviour, and to trace out the relationships in the organic and inorganic world which have determined its survival. Much is mere specu- lation; 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. v A2 vi PREFACE 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. CONTENTS PAGE CHAPTER I INTRODUCTION . A : : ‘ ‘a a 1 CHAPTER II THE DIsPosITIonN TO SECURE A TERRITORY ° : 20 CHAPTER III Tue Disposition TO DEFEND THE TERRITORY ; 73 CHAPTER IV THE RELATION OF SONG TO THE TERRITORY ; . rts CHAPTER V THE RELATION OF THE TERRITORY TO THE SYSTEM OF REPRODUCTION . A A : : 3 2GS CHAPTER VI THE WARFARE BETWEEN DIFFERENT SPECIES AND ITS RELATION TO THE TERRITORY F ; - . 216 CHAPTER VII THE RELATION OF THE TERRITORY TO MIGRATION . 269 INDEX . : é ¥ ‘ ; ‘ x 02 vil > a a ee oe” ve oar LIST OF ILLUSTRATIONS Face page A pair of Lesser Spotted ia erat attacking a Great Spotted Woodpecker ; : ‘ Frontispiece Territorial flight of the Black-tailed Godwit Competition for territory is seldom more severe than among cliff-breeding seabirds, and the efforts of individual Razorbills to secure positions on the crowded ledges lead to desperate struggles Male Blackbirds fighting for the possession of territory. The bare skin on the crown of the defeated bird shows the nature of the injuries from which it succumbed Male Cuckoos fighting before the arrival of a female Two pairs of Pied Wagtails nee in defence of their territories . ; ‘ 5 : Long-tailed Tit: males fighting for the possession of territory. The feathers have been torn from the crown of the defeated and dying rival . A battle between two pairs of Jays . The Female Chaffinch shares in the defence of the ee and attacks other females ‘ ‘ Peregrine Falcon attacking a Raven . A battle between a pair of Green Woodpeckers and a Great Spotted Woodpecker for the possession of a hole in an oak-tree , : : E Plans of the Water-meadow showing the Territories 54 64 74 82 86 96 106 110 216 238 occupied by Lapwings in 1915 and 1916 Between 58 and 59 SCIENTIFIC NAMES OF BIRDS MENTIONED IN THE TEXT Raven . Carrion-Crow Hooded Crow Rook Magpie Jay : Chough Starling Greenfinch . Hawfinch House-Sparrow Chaffinch Brambling Linnet . Corn-Bunting Yellow Bunting Cirl Bunting Reed-Bunting Sky-Lark Pied Wagtail Tree-Pipit Meadow-Pipit Great Titmouse Blue Titmouse Long-tailed Titmouse Red-backed Shrike Whitethroat . xi Corvus corax. Corvus corone. Corvus corniz. Corvus frugilegus. Pica pica. Garrulus glandarius rufitergum. Pyrrhocorax pyrrhocorax. Sturnus vulgaris. Chloris chloris. Coccothraustes coccothraustes. Passer domesticus. Fringilla celebs. Fringilla montifringilla. Acanthis cannabina. Emberiza calandra,. Emberiza citrinella. Emberiza cirlus. Emberiza scheniclus. Alauda arvensis. Motacilla lugubris. Anthus trivialis. Anthus pratensis. Parus major newtoni. Parus ceeruleus obscurus. Aigithalus caudatus roseus. Lanius collurio. Sylvia communis. xii SCIENTIFIC NAMES OF BIRDS Lesser Whitethroat Blackcap ; Geacenee Warbler : Savi’s Warbler Reed-Warbler Marsh-Warbler Sedge-Warbler Willow-Warbler Wood-Warbler Chiffchaff Song-Thrush Redwing Blackbird Redstart Redbreast Nightingale . Stonechat Whinchat Wheatear Hedge-Sparrow Wren Spotted Flyeabeher Swallow Martin . Sand- Martin Great Spotted paren A Lesser Spotted Woodpecker. Green Woodpecker Cuckoo Tawny Owl . Buzzard Sparrow-Hawk Peregrine Falcon . Merlin. Kestrel . Sylvia curruca. Sylvia atricapilla. Locustella nevia. Locustella luscinioides. Acrocephalus scirpaceus. Acrocephalus palustris. Acrocephalus schaenobenus. Phylloscopus trochilus. Phylloscopus sibilatrix. Phylloscopus collybita. Turdus musicus clark. Turdus iliacus. Turdus merula. Pheenicurus phoenicurus. Erithacus rubecula melophilus. Luscinia megarhyncha. Saxicola rubicola. Saxicola rubetra. (nanthe cenanthe. Accentor modularis. Troglodytes troglodytes. Muscicapa striata. Hirundo rustica. Delichon urbica. Riparia riparia. Dryobates major anglicus. Dryobates minor. Picus viridis. Cuculus canorus. Strix aluco. Buteo buteo. Accipiter nisus. Falco peregrinus. Falco cesalon. Falco tinnunculus. SCIENTIFIC NAMES OF BIRDS Shag. f , Wild Duck Snipe . ‘ . Dunlin . BGas| \& Redshank Black-tailed Godwit Curlew. Whimbrel ‘ American Golden Plover Lapwing. . Oyster-Catcher Herring-Gull Kittiwake Razorbill : Guillemot , : Pati: 5 J Fulmar : “i Water-Rail , ; Corn-Crake . Moor-Hen Coot. . 5 Wood- Pigeon Turtle-Dove. Partridge : Black Grouse 3 Red Grouse , : Phalacrocorax graculus, Anas boschas. Gallinago gallinago. Tringa alpina. Machetes pugnac. Totanus totanus. Limosa limosa., Numenius arquata. Numenius phaeopus. Charadrius dominicus. Vanellus vanellus. Hematopus ostralegus, Larus argentatus. Rissa tridactyla. Alca torda, Uria troille. Fratercula arctica, Fulmarus glacialis. Rallus aquaticus. Crex crex. Gallinula chloropus. Fulica atra. Columba palumbus. Streptopelia turtur. Perdix perdix. Lyrurus tetrixa britannicus. Lagopus scoticus. xili TERRITORY IN BIRD LIFE CHAPTER |! INTRODUCTION In his Manual of Psychology Dr Stout reminds us that ‘Human language is especially con- structed 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 con- nection with the sexual life of birds is open to the danger which we are here asked to guard against, and I propose, therefore, before attempt- ing 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 1 2 INTRODUCTION a simple mental process we conceive of a state in bird life analogous to that which we know to be customary amongst ourselves. Now, although the term ‘breeding territory,” when applied to the sexual life of birds, is not alto- gether 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 indi- vidual in the attainment of reproduction, has been gradually evolved to meet the exigencies of diverse circumstances. Regarded thus, we avoid the risk of conceiving of the act of secur- ing 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 sexual 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” ean only be held to apply to certain forms of life; for where the young have to be cared for, SECURING TERRITORY 3 fostered, and protected from molestation for periods of varying lengths, the actual discharge of the sexual function marks but one stage in a process which can only succeed if all the con- tributory 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 sexual func- tion, 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 sexual 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 exist- ence 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 detach- ments travelling from one district to another ; by isolated individuals deserting this place for B 4 INTRODUCTION 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 over- come. 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 sexual 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 SECURING TERRITORY 5 one motive—the procuring of food. And since it is to the advantage of all that the indi- vidual should be subordinated to the welfare of the community as a whole there is no dis- sension, 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 develop- ing 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 terri- tories, 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 6 INTRODUCTION the purpose of the theory I shall give ex- pression 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 dis- cussion, for that part of the inherited nature which has been organised to subserve a specific biological purpose—strict compliance with the rules of psychological analysis 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 attain- ment 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 func- tional activity at much the same stage of sexual 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 re- production. 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 breed- BOUNDARIES DETERMINED BY HABIT 7 ing 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 suscep- tible 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 B2 8 INTRODUCTION recourse to so complex a principle of explana- tion, 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 repetition 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 pre- judice 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 estab- lished 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 BOUNDARIES DETERMINED BY HABIT 9 headquarters, especially as regards the direction, frequency, and extent of the journeys; and we discover not only that these journeys pro- ceed 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 con- tinued observation discover that these limits are seldom exceeded, that definition grows more and more pronounced, 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 repetition certain performances become stereotyped, cer- tain paths fixed, and a routine is thus estab- lished 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 circum- stances 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 10 INTRODUCTION 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 sex, leads to a vast amount of strife. Nowhere in the animal world are conflicts more frequent, more prolonged, and more determined than in the sexual life of birds; and though they are acknowledged to be an important factor in the life of the individual, yet there is much differ- ence 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 competition thus created would be a means of maintaining efficiency, the females, by common consent, are supposed to supply the condition DEFENCE OF THE TERRITORY 11 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 sex, so long were there grounds for hoping that their origin might be traced to such competition. 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 sex 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 12 INTRODUCTION 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 sexes at the very commencement of the sexual process. What is the immediate consequence? Since the male isolates itself, it follows, if the union of the sexes 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 reproduc- tion 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 assists in the attain- ment 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 RELATION OF SONG TO THE TERRITORY 13 the other, and impossible to regard the voice as the medium through which an effectual union of the sexes 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 occupa- tion 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 sexual behaviour is concerned. So that just at the moment when the sexual impulse of the female is most sus- ceptible 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 assured to her; for with multitudes of individuals striving to pro- create 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. Competition 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 14 INTRODUCTION assistance 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 sexual behaviour regarded as so many distinct phenomena requir- ing 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 adjust- ments 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 ORGANIC AND INORGANIC RELATIONSHIPS 15 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 reproduc- tion. 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 con- ditions 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 16 INTRODUCTION inhabiting a certain piece of marsh are divided into two classes, 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 ~ competition in every direction, will be com- pelled 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 con- ditions under which it is reared, observing the proportion of time it passes 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. ORGANIC AND INORGANIC RELATIONSHIPS 17 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 assemble 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 space 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 space occupied by each individual is therefore a matter of urgent importance. A few square feet of rock sufficient for the im- mediate 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 circumstances under which these cliff-breeding forms dwell does, however, 18 INTRODUCTION 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. Com- petition 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 mani- festation of the revival of the sexual instinct was to be found in the movements under- taken 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 EXTENSION OF BREEDING RANGE 19 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 related- ness. So long as we fix our attention solely upon the magnitude of the distance traversed the suggestion may seem a fanciful one. Never- theless, if the battles between males of the same species are directly related to the occupa- tion 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 competition 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 competition 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 THOosE 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 circumstances 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 Woodpecker utters its monotonous call from the accustomed oak; the 20 HOW BEHAVIOUR IS DETERMINED 21 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 sexual life of the individual ; and the attach- ment 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 signifi- cance estimated at its true value, it is above all things necessary to refrain from appealing to any one of the emotions which we are accus- tomed to associate 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 sexual life of birds is the important one I believe it to be, it follows that the 22 DISPOSITION 'TO SECURE A TERRITORY 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 sexual 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 sexual cycle. Here, then, we meet with a difficulty so far as direct observation is con- cerned, 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 sexual 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 BEHAVIOUR OF MIGRATORY MALES — 23 with which the initial stage in the sexual process was marked off, as a result of the incidence cf migration, would go far towards removing much of the obscurity which appeared to surround the earlier stages of the breeding problem in the ease 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 passes 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 €2 24 DISPOSITION TO SECURE A TERRITORY more closely, it will be found that in nearly every case they belong to the male sex. 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 cer- tain 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. Gitke 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 sexes occur mixed, 2.¢., 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 cock 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 Migra- tion, 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 BEHAVIOUR OF MIGRATORY MALES 25 cases even weeks, before their consorts.” Some interesting details were given in British Birds’ in regard to the sex 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 sexual 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 constituted 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 isola- tion, remained with the females and increased their opportunities for developing that mutual appreciation which, by some, is held to be a 1 June 1915, R. M. Barrington. 26 DISPOSITION TO SECURE A TERRITORY necessary prelude to the completion of the sexual act, and to which close companionship would tend to impart a stimulus. In thus speaking, however, we assume that the revival of the sexual 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 assumption is based upon fact, and how much is due to questionable inference. All that can be definitely asserted 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 sexual organs. Beyond this there is nothing to go upon. Yet if the term “sexual 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 assumption 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 sexual 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 BEHAVIOUR OF RESIDENT MALES 27 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 sexual 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 environ- ment 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 principally amongst the smaller species—the Finches and the Buntings—which often pass 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 28 DISPOSITION TO SECURE A TERRITORY 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 pass 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; other- wise the earlier symptoms of any disposition to secure a territory may quite possibly be over- looked in the search for its breeding haunts. In open weather Reed-Buntings pass 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 BEHAVIOUR OF RESIDENT MALES 29 ground where the Juncus communis grows in abundance, to the dense masses of the common reed (Arundo phragmites), and such like places. During the winter, the male’s routine of exist- ence is of asomewhat 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 30 DISPOSITION 'TO SECURE A TERRITORY 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. ‘The male does not appear in its few acres suddenly and remain there permanently as does the migrant; at first it may not even roost in the prospective territory. ‘The course of procedure is somewhat as follows :—At dawn it arrives and for a while utters its song, preens its feathers, or searches for food ; then it vanishes, BEHAVIOUR OF RESIDENT MALES 31 rising into the air and flying in one fixed direction as far as the eye can follow, until it becomes a speck upon the horizon and is ultimately lost to view. During these excursions it rejoins the small composite flocks which still frequent the fields and farm buildings. For a time the hedgerow is deserted and the bird remains with its companions. But one does not have to wait long for the return; it reappears as suddenly as it vanished, flying straight back to the few acres which constitute its territory, back even to the same gate-post or railing, where it again sings. This simple routine may be repeated quite a number of times during the first two hours or so of daylight, with, of course, a certain amount of variation; on one occasion the bird may be away for a few minutes only, on another for perhaps half an hour, whilst sometimes it will fly for a few hundred yards, hesitate, and then return—all of which shows clearly enough that these few acres possess some peculiar significance and are capable of exercising a powerful influence upon the course of its behaviour. And so the disposition in relation to the territory becomes dominant in the life of the bird. Or take the case of the Chaffinch. In winter large or small flocks can be found in many varied situations. But in the latter part of February, or the early days of March, these flocks begin to disperse. At daylight males can then be observed in all kinds of situations, either calling loudly, uttering their spring note, 32 DISPOSITION TO SECURE A TERRITORY or exercising their vocal powers to the full; and it will be found that, in the majority of instances, these males are solitary individuals, that they pass the early hours of the morning alone, and that their normal routine of calling, singing, or searching for food, is only interrupted by quarrels with their neighbours. The same locality is visited regularly—not only the same acre or so of ground, but even the same elm or oak, has, as its daily occupant, the same cock Chaffinch. And temporary desertions from the territory occur also, much like those referred to in the life of the Bunting, but perhaps not so frequently. One has grown so accustomed during the dark days of winter to the sociable side of Chaffinch behaviour—to the large flocks searching for food, to the endless stream of individuals returning in the evening to roost in the holly-trees, to the absence of song— that this radical departure from the normal routine comes as something of a surprise; for the days are still short, the temperature is still low, the nesting season is still many weeks ahead, and yet for part of the day, and for just that part when the promptings of hunger must be strongest, the male, instead of joining the flock, isolates itself and expends a good deal of energy in insuring that its isolation shall be complete. And in place of the silence we hear from all directions the cheerful song uttered with such marked persistency that it almost seems as if the bird itself must be aware that by doing so it was advertising the BEHAVIOUR OF RESIDENT MALES 33 fact of its occupation of a territory. This is surely a remarkable change, and the females in the meantime continue their winter routine. One other example. The monotonous call of the Greenfinch is probably familiai to all. In winter these birds accompany other Finches and form with them flocks of varying sizes, but in the spring the flocks disperse, and the Green- finch, in common with other units of the flock, alters its mode of life. But whereas the Chaffinch or the Bunting begins to acquire its territory in February, the Greenfinch only does so in April. When the organic changes do at length begin to make themselves felt, the male seeks a position of its own, and having found one remains there, uttering its characteristic call. But owing probably to the fact that it is much later than the afore- mentioned species in acquiring a territory, temporary desertions are not so much in evi- dence. The species is so very plentiful, and the bird is so prone to nest in gardens and shrubberies surrounding human habitations, that this seasonal change in its routine of existence cannot fail to be noticed. One can hear its call in every direction, one can watch the same individual in the same tree; and it is the male that is thus seen and heard, the female appears later. Thus the behaviour falls into line with that of the Bunting or the Chaffinch. The behaviour of these resident species throws some light upon the early arrival of the 34 DISPOSITION TO SECURE A TERRITORY males which we are endeavouring to explain in the case of the migrants. Let us see how their actions compare. The male resident deserts the female early in the year and establishes itself in a definite position, where it advertises its presence by song; the male migrant travels from a great distance, arrives later, and also establishes itself in a definite position, where it, too, advertises its presence by song. ‘The male resident passes only the earlier part of the day in its territory at the commencement of the period of occupation ; the male migrant remains there continuously from the moment it arrives. ‘The male resident deserts its territory at intervals, even in the morning ; the male migrant betrays no inclina- tion to do so. Thus there is a very close correspondence between the behaviour of the two, and what difference there is—slight after all—cannot be said to affect the main biological end of securing territory. One is apt to think of the problem of migration in terms of the species instead of in terms of the individual. One pictures a vast army of birds travelling each spring over many miles of sea and land, and finally establishing themselves in different quarters of the globe; and so it comes about, I suppose, that a country or some well-defined but extensive area is regarded as the destination, the ultimate goal, of the wanderers. But the resident male has a journey to perform, short though it may be; it, too, has a destination to reach, neither a country nor a locality, but a place wherein the rearing of offspring can MALES ARRIVE BEFORE FEMALES 35 be safely accomplished, and it, too, arrives in that place in advance of the female. With these facts at our disposal, we will endeavour to find an explanation. It is unlikely that specialised behaviour would occur in genera- tion after generation under such widely divergent conditions, and, moreover, expose the birds to risk of special dangers, if it were but an hereditary peculiarity to which no meaning could be attached. Hence the appearance of the males in their breeding haunts ahead of the females becomes a fact of some importance, and suggests that the extensive journey in the one case, and the short journey in the other, may both have a similar biological end to serve. Darwin evidently attached importance to this difference between the males and the females in their times of arrival. In _ the Descent of Man he referred to it as follows: “Those males which annually first migrated in any country, or which in spring were first ready to breed, or were the most eager, would leave the largest number of offspring; and _ these would tend to inherit similar instincts and constitutions. It must be borne in mind that it would have been impossible to change very materially the time of sexual maturity in the females without at the same time interfering with the period of the production of the young —a period which must be determined by the season of the year.” Newton suggested the following explanation’: “It is not difficult to 1 Dictionary of Birds, p. 556. D 36 DISPOSITION TO SECURE A TERRITORY imagine that, in the course of a journey pro- longed through some 50° or 60° of latitude, the stronger individuals should outstrip the weaker by a very perceptible distance, and it can hardly be doubted that in most species the males are stouter, as they are bigger than the females.” Granting that the males are the stronger, how can this account for their outstripping the females by a week, ten days, or even a fortnight, in a journey of perhaps 1500 miles? To expect the birds to accom- plish such a distance in seven days is surely not estimating their capabilities too highly, and any slight inequality in the power of flight or endurance could give the males an advantage of a few hours only. But this ex- planation, based upon inequalities in the power of flight and endurance on the one hand, and the magnitude of the distance traversed on the other, cannot afford a solution of the behaviour of the resident males, and is less likely, there- fore, to be a true:solution of that of the migrants. There is another theory, simple enough in its way, which will probably occur to many. It is based on the assumption that the males reach sexual maturity before the females; and it is contended that the functioning of the instincts which contribute towards the biological end of reproduction depend upon the organic changes which the term “sexual maturity” is held to embrace, and that, inasmuch as the migratory instinct belongs to the group of such instincts, MALES ARRIVE BEFORE FEMALES 37 the males must be the first to leave their winter quarters. What is meant by the ‘“‘ migratory instinct ” ? To speak of it as one of the instincts concerned in reproduction is not enough. Reproduction involves the actual discharge of the sexual function, which involves the females; but the first visible manifestation of organic change in the male is its desertion of the females. Yet this is the behaviour which is referred to as the “ migratory instinct,” and which comes into play, according to this theory, because the bird has reached sexual maturity. Manifestly we must have some clear understanding as to what these terms represent. That organic changes deter- mine the functioning of certain definite instincts at certain specified times there can be no doubt ; that these changes may occur at a somewhat earlier date in the male than in the female is more than probable, but that this explains the behaviour in question I do not believe. One wants to know why the changes should occur earlier in the male, what disposition it is which first comes into functional activity, and to what such disposition is related. It may, however, be urged that, after all, this apparent eagerness to reach the breeding grounds is but a modification of hereditary pro- cedure under the guiding hand of experience. What more likely result would follow from the enjoyment associated with previous success in the attainment of reproduction than a craving to repeat the experience? What stronger incentive 38 DISPOSITION TO SECURE A TERRITORY to a hurried return could be imagined? It must be admitted that there are certain facts which might be used in support of an appeal to experience as a reasonable explanation. For example, the first males to arrive often display that richness of colouring which is generally supposed to indicate a fuller maturity. Gitke even speaks of the “‘most handsome old birds being invariably the first to hasten back to their old homes.” But if experience is a factor, if some dim recollection of the past is held to explain the hurried departure of the male migrant, one wants to know with what such recollection is associated. Is it associated with the former female, or with the former breeding place, or with both? I take it that any recol- lection, no matter how vague, must be primarily associated with the particular place wherein reproduction had previously been accomplished ; and I grant that if the first individuals to appear were invariably the older and experienced birds, their early return might be explained on the basis of such an association. But if there is reason to believe that a proportion are young birds on the verge of carrying out their instinc- tive routine for the first time, then we cannot appeal to past experience in explanation of their behaviour. The age of a bird is difficult to determine. Experience leads me to believe that some of the males that arrive before the females are birds born the previous season; one finds, for instance, individuals with plumage of a duller hue, MALES ARRIVE BEFORE FEMALES 39 which denotes immaturity, amongst the first batch of arrivals. But though plumage may sometimes be a satisfactory guide, yet to rely upon it alone, or upon a more perfect develop- ment of feather, is to exceed the limits of safety. How, then, can we ascertain whether all the males that arrive before the females have had some previous experience of reproduction ? Well, we take a particular locality and note the migrants that visit it year after year, and we find that the respective numbers of the different species are subject to wide annual fluctuations. Not every species lends itself to an inquiry of this kind: some are always plentiful and fluctua- tion is consequently difficult to discern; others are scarce and variation is easily determined. Those which are of local distribution but con- spicuous by their plumage, or easily traced by the beauty or the peculiarity of their song, afford the more suitable subjects for investiga- tion. For example, the Grasshopper-W arbler, Marsh-Warbler, Nightingale, Corncrake, Red- backed Shrike, or Whinchat have each some distinctive peculiarity which makes them con- spicuous, and each one is subject to marked fluctuation in numbers. ‘The small plantation or wooded bank may hold a Nightingale one year, but we miss its song there the next; the osier bed or gorse-covered common which vibrates with the trill of the Grasshopper-Warbler one April is deserted the following season; the plantation which is occupied by a_ host of common migrants this summer may be enlivened D2 40 DISPOSITION TO SECURE A TERRITORY next year by the song of the rarer Marsh- Warbler also; and so on. ‘The fluctuation is considerable: we observe desertion on the one hand, appropriation on the other, and yet males appear before females whether the particular plantation, osier bed, or swamp had been in- habited or not the previous season. This fact is not without significance. It shows that similar conditions prevail both amongst the males that appropriate breeding grounds new to them, and amongst those that return to some well- established haunt; and on the assumption that the earlier arrivals are experienced males, the same birds evidently do not return to the same place year after year. Granting, then, that the males which appropriate new breeding-grounds are young birds, how can their earlier arrival be explained in terms of past experience; and granting that they are old, and_ therefore experienced, how can it be explained in terms of association ? Again, it may be urged that if there is some biological end to be furthered by this hurried return, and if recollection of past experience is a means towards that end, such recollection need not necessarily be associated with a definite place, but only in a vague way with the whole series of events leading up to reproduction—in which series the migratory journey may even have acquired meaning, Whether there be any recollection of a previous journey or of a nest with young, I do not know. But the young bird is capable of performing its journey, of MALES ARRIVE BEFORE FEMALES 41 building its nest, and of rearing its young ante- cedent to experience—racial preparation has fitted it thus far; why then exclude the other event in the series, the earlier departure of the male, from hereditary equipment? If the journey were a casual affair without any goal attaching to it, if the males upon arrival wandered about in search of a mate, there would be some ground for thinking that a vague recollection of the whole former experience was sufficient to explain the hurried return; but since the pleasurable effect of association, founded upon previous experience of a definite place, cannot well be established, and since it is so difficult to study the objective aspect of the behaviour in question without coming to the conclusion that the journey is related to the appropriation of a place suitable for the rearing of offspring, one is tempted to ask whether the hurried return may not also be so related. Now the males of some of the migratory species, especially of those which are accus- tomed to return to their breeding haunts early in the season, are called upon to face greater dangers and have a greater strain imposed upon their strength by starting forth upon their journey ten days or a fortnight before their prospective mates. The blizzards which so often sweep across the northern parts of Europe in the latter half of March, destroying in their course the all too scanty supply of insect life, may take toll of their numbers; or the westerly gales, which are not infrequent at that period, 42 DISPOSITION TO SECURE A TERRITORY may meet them in mid-ocean and add to the perils of their journey; or the temperature of the previous weeks may have been sufficiently low to arrest the development of insect life— and yet males are annually exposed to these risks in hurrying to their breeding grounds. For what purpose? The answer will -largely depend upon the way in which we regard those few acres wherein a resting place is ultimately found. For myself, I believe that they are of importance, inasmuch as the securing of a place suitable for the rearing of offspring is a primary condition of success in the attain- ment of reproduction; and if this be so, it is evident that the interests of the race will be better served by the males making good this first step before the females are ready to pair, otherwise they might oscillate between two modes of behaviour, created by the premature functioning of conflicting impulses. The different steps in the process seem to follow one another in ordered sequence. The male inherits a disposition—which for us, of course, has prospective meaning—to seek the appropriate breeding ground and there to establish itself; and as early a functioning of this disposition as possible, consonant with the conditions of existence in the external environ- ment, may have been evolved for the following reasons — firstly, the earlier individuals will meet with less interference wherever they may settle, every locality will be open to them, every acre free, their only need being that MALES ARRIVE BEFORE FEMALES 43 particular environment for which racial pre- paration has fitted them. In the second place, being already established when other males appear upon the scene, and advertising their presence by song, they will be less liable to molestation; thirdly, in those cases in which a long journey is undertaken, they will have ample time to recover from the fatigue, and, if attacked by later arrivals, will thus be in a better position to defend their territories; and lastly, a greater uniformity in their distribution will be insured before the females begin their search. There is, besides, another good reason for thinking that the earlier males will have an advantage. We will assume—and from the abundant evidence supplied by the marking of birds, it is quite a reasonable assumption— that there is a tendency, generally speaking, for individuals to return to the neighbourhood of their birthplace, or to the place in which they had previously reared their offspring. Now the earlier arrivals will have no difficulty” in securing territories; those that come later may have to search more diligently, still they will gain all that they require so long as any available space remains. ‘Then comes the point when all suitable ground is occupied, and yet there are males to be provided for. What will be the position of these males? Urged by their inherited nature, they will leave the district and possibly continue their search into those adjoining, only, however, to add to the diffi- 44 DISPOSITION TO SECURE A TERRITORY culties of the males there similarly situated ; and even allowing that they are at length successful in establishing themselves, what are their prospects of securing mates? Since the earlier females will not extend their wander- ings farther than is absolutely necessary, but will pair whenever the opportunity for doing so arises, it is to the later females, forced onwards by competition, that the late males must look for mates; so that when at length pairing does take place, much valuable time will have been lost. The disadvantages which the late arrivals have to face are therefore great, and it is probable that the percentage which attain to reproduction will on the average be somewhat lower than the percentage in the case of the earlier arrivals. The district in which my observations have been made lies well within the limits of the breeding range of most of our common species, and it is not surprising that I should have met with little evidence of failure to breed as a result of failure to secure territory. Some interesting information was supplied to me, however, by the late Robert Service. He found, in certain seasons in Dumfriesshire, flocks of from ten to fifty unmated Sedge-Warblers, which, from the time of their arrival in May until the middle of July, haunted reed-filled spaces along stagnant streams. These flocks appeared to him to be composed of loosely-attached individuals of a migrant flock that had failed to find things IDENTITY OF THE MALE 45 congenial enough to entice them to disperse. But may they not have been composed of males that had failed to secure territories, or of females that had-failed to discover males in possession of territories, or of both ? We have seen that, in the case of many species, each male establishes itself in a particular place at the commencement of the breeding season, even though this may mean a partial or perhaps a complete severance from former companions. We must now discuss this fact in greater detail because it is opposed to the views often held regarding the sexual behaviour of birds, and is manifestly of impor- tance when considering the theory of breeding territory. First, however, there is a point which requires some explanation. I speak of the same male being in the same place. How can I prove its identity? In the first place it is highly improbable that a bird which roams _ about within the same small area of ground, makes regular use of a certain tree and a certain branch of that tree, and observes a_ similar routine day after day, can be other than the same individual. But, apart from this general consideration, are there any means by which individuals of the same species can be identified ¢ Well, there is variation in the plumage. Supposing we take a dozen cock Chaffinches and examine them carefully, we shall find slight differences in pattern and in colour—more grey — 46 DISPOSITION TO SECURE A TERRITORY here or a duller red there, as the case may be— and though these differences may not be sufficient to enable us to pick out a bird at a distance, they are nevertheless conspicuous when it is close at hand. Then again there is variation in the song; and the more highly developed the vocal powers the greater scope there is for variation. But even the phrases of a simple song can be split up and recombined in different ways. If one were asked casually whether the different phrases of the Reed- Bunting’s song always followed one another in the same sequence, the answer would probably be that they certainly did so, whereas the bird is capable of combining the few notes it possesses in a surprising number of different ways. And lastly, there are differences in just the particular way in which specific behaviour, founded upon a congenital basis, is adapted by each individual to its own special environment. Racial pre- paration determines behaviour as a whole, but the individual is allowed some latitude in the execution of details which are in themselves of small moment—the selection of a particular tree as a headquarters and a particular branch upon that tree, the direction of the distant excursion, and the direction of the limited wanderings within the small area surrounding the head- quarters which in the course of time determine the extent of the territory, are matters for each individual to decide when the occasion for doing so arises. Moreover instances of abnormal coloration or abnormal song are not IDENTITY OF THE MALE 47 rare, and they are valuable since they place the identity of the individual beyond dispute. I can recall the case of a Willow- Warbler whose song was unlike that of its own or any other species, and of a Redbreast whose voice puzzled me not alittle. I can recollect alsoa male Yellow Bunting whose foot was injured or deformed. Of this bird’s behaviour I kept a record for two months or so; and inasmuch as it inhabited a roadside hedge, and was of fearless disposition, the deformed foot could plainly be seen when- ever it settled upon the road to search for food. Identification is not, therefore, a difficulty. There is always some small difference in colour or in song, or some well-defined routine which makes recognition possible. Owing to their great powers of locomotion, birds have generally been regarded as wanderers more or less; anything in the nature of a fixed abode, apart from the actual nest, having been accounted foreign to their mode of life; and even the locality immediately surrounding the nest has not been apprehended as possessing any meaning for the owner of that nest. No doubt the supply of food determines their movements for a considerable part of the year; they seek it where they can find it, here to-day, there to-morrow—in fact few species fail to move their quarters at one season or another, so that there is much truth in the notion that birds are wanderers. Yet to suppose that every individual one sees or hears—every Lapwing on the meadow, or Nightingale in the withy 48 DISPOSITION TO SECURE A 'TERRITORY bed—is in that particular spot just because it happens to alight there as it roams from place to place, is to take a view which the observed facts do not support. For as soon as the question of reproduction dominates the situation, a new condition arises, and the habits formed during the previous months are reversed, and the males, avoiding one another, or even becoming actively hostile, prefer a life of seclusion to their former gregariousness—all of which occurs just at the moment when we might reasonably expect them to exhibit an increased liveliness and restlessness as a result of their endeavour to secure mates; and so universal is the change that it might almost be described as an accompaniment of the sexual life of birds generally. That the Raven and certain birds of prey exert an influence over the particular area which they inhabit has long been known, and it has been recognised more especially in the case of the Peregrine Falcon, possibly because the bird lives in a wild and attractive country, and, forcing itself under the notice of naturalists, has thus had a larger share of attention devoted to its habits. Moreover, when a species is represented by comparatively few individuals, and each pair occupies a comparatively large tract of country, it is a simple matter to trace the movements and analyse the behaviour of the birds. ‘There is a rocky headland in the north-west of Co. Donegal comprising some seven miles or so of cliffs, where three pairs of Falcons and two pairs of Ravens have nested for many years. ISOLATION OF THE MALE 49 Each year the different pairs have been more or less successful in rearing their young; each year the young can be seen accompanying their parents up to the time when the sexual instinct arises ; and yet the actual number of pairs is on the whole remarkably constant, and there is no perceptible increase. It seems as if the numbers of three and two respectively were the maxi- mum the headland could maintain. But this is no exceptional case; it represents fairly the conditions which obtain as a rule amongst those species, granting, of course, a certain amount of variation in the size of each terri- tory determined by the exigencies of diverse circumstances. If we take a given district, and devote our attention to the smaller migrants that visit Western Europe each returning spring for the purpose of procreation, we shall find that the movements of the males are subject to a very definite routine. This, however, is not true of every male; some may be wending their way to breeding grounds at a distance; others may be seeking the particular environment to which they;may be adapted ; others again, having found their old haunts destroyed, may consequently be seeking new. Of all this there is evidence. Small parties of Chiffchaffs pass through a district on their way to other breeding grounds, flitting from hedge to hedge as they move in a definite direction with apparently a definite purpose ; Reed-Warblers settle in a garden or plantation, 50 DISPOSITION TO SECURE A TERRITORY eminently unsuited to their requirements, and disappear ; Wood-Warblers arrive in some old haunt, and finding it no longer suitable for their purpose, seek new ground. So that plenty of individuals are always to be found, which, for the time being at least, are wanderers. In the district which I have in mind, the wandering males form only a small part of the incoming bird population. The majority of individuals that fall under observation are those that have made this particular district their destination ; and in doing so, they may possibly have been guided by their experience as owners or inmates of former nests, for it cannot be doubted that a return to the neighbourhood of the birthplace would lead to a more uniform distribution and therefore be advantageous, and the tendency to do so might consequently have become interwoven in the tissue of the race. How, then, do they behave? A certain amount of movement, an interchanging of positions, even though restricted to an area defined, let us say, by experience, might be expected under the circumstances—that, however, is not what we find ; we observe the available situations plotted out into so many territories, each one of which is occupied by a male who passes the whole of his time therein. Take whatever species we will—Whitethroat, Whinchat, Willow-Warbler, Red-backed Shrike, it matters not which, for there is no essential difference in the general course of procedure—this condition will be found to prevail. Generally speaking, the — ISOLATION OF THE MALE 51 behaviour in relation to the territory can be studied more conveniently where a number of individuals of the same species have established themselves in proximity to one another. Such species as the Chiffchaff, Willow-Warbler, or Wood-Warbler are often sufficiently common to allow of three or more of their respective males being kept in view at the same time; and the disposition to occupy a definite position can be readily observed. ‘The Reed-Warbler is a suit- able subject for an investigation of this kind ; for since it is restricted by its habits to localities wherein the common reed (Arundo phragmites) grows in abundance, and since such localities are none too plentiful and often limited in extent, the area occupied by each individual is necessarily small—if it were not so the species would become extinct. Hence it is a simple matter to study the routine of the different individuals and to mark the extent of their wanderings. In this way the males of all the Warblers that breed commonly in Great Britain establish themselves, each one in its respective station at the respective breeding ground; so, too, do those of many other migrants—for example, the Whinchat, Wheatear, Tree- Pipit, and Red - backed Shrike. All of these, it is true, are common species—numbers of individuals can often be found in close proximity—and therefore it may be argued that they keep to one position more from pressure of population than from any inherited disposition working towards that end. E 52 DISPOSITION TO SECURE A TERRITORY But the rarer species behave similarly. Districts frequented by the Marsh-Warbler and offering plenty of situations of the type required by the bird are often inhabited by a few members only, and yet the disposition to remain in a definite position is Just as marked. You will say, however, that these smaller migrants have no exceptional powers of flight ; that they have besides just completed a long and arduous journey; and you will ask why they should be expected to wander, whether it is not more reasonable to expect that, in order to overcome their fatigue, they should remain where they settle. The Cuckoo is a wanderer in the wider sense of the term, and is gifted with considerable powers of flight. Upon arrival the male flies briskly from field to field, showing but little signs of weariness; yet we have only to follow its movements for a few days in succession to assure ourselves that the bird is no longer a wanderer ; for just as the Warbler or the Chat moves only within a definitely delimited area, so the male Cuckoo, strange as it may seem, restricts itself to a particular tract of land. The area over which it wanders is often con- siderable and consequently it is not possible to keep the bird always in view, but inasmuch as the variation in the voices of different individuals is quite appreciable, identification is really a simple matter. If we cannot keep the bird in sight, we can trace its movements by sound and mark the extent of its wanderings, which by repetition become more and more ISOLATION OF 'THE MALE 53 defined, until a belt of trees here, or an orchard there, mark a rough and rarely passed boundary line. Let us take another example from the larger migrants — the Black-tailed Godwit, a bird common enough in the Dutch marshes but no longer breeding in this country. On suitable stretches of marsh land, numbers will be found in proximity one to another after the manner of the Lapwing, each male occupying a definite space of ground wherein it passes the time preening, searching for food, or in sleep— though at the same time keeping a strict watch over its territory. Now the preference shown for a particular piece of ground, and the deter- mination with which it is resorted to, is the more remarkable when we take into considera- tion the specific emotional behaviour arising from the seasonal sexual condition. This behaviour is expressed in a peculiar flight. The bird rises high in the air, circles round with slowly beating wings above the marsh, and utters a call which, as far as my experience goes, is characteristic of the performance. The air is often full of individuals circling thus even beyond the confines of the marsh, for a male does not limit its flight to a space immediately above its territory; but nevertheless careful observation will show how unerringly each one returns to its own position on the breeding ground, no matter how extensive the aerial excursion may have been. And so, when the males of the smaller migrants confine their 54 DISPOSITION TO SECURE A TERRITORY movements to an acre of ground at the com- pletion of their long journey, they are acting no more under the influence of fatigue than the Cuckoo, which keeps within certain bounds yet flies about briskly, or the Godwit which, though holding to its few square yards on the ground, executes most tiring and extensive flights above the marsh. Of all the migrants, however, the behaviour of the Ruff is perhaps the most strange, and though it has long been known that these birds have their special meeting places where they perform antics and engage in serious strife, yet it is only within recent years that the primary purpose of these gatherings has been ascertained —that purpose being the actual discharge of the sexual function. Mr Edmund Selous has carried out some exhaustive investigations into their activities at the meeting places, and he makes it clear that each bird has its allotted position. He says, for example, that “It begins to look as though different birds had little seraglios of their own in different parts of the ground,” that ‘each Ruff has certainly a place of its own,” or again that “this Ruff indeed, which I think must be a tender-foot, does not seem to have a place of its own like the others.” Nevertheless it is only at the meeting places that they have their special positions; there is no evidence to show that each one has a special territory, wherein it seeks its food, as the Warbler has, and therefore some may think that we are here confronted with behaviour of a ISOLATION OF THE MALE 55 different order. But we must bear in mind that the process has been adjusted to meet the requirements of different species: the size of the territory, the period of its daily occupation, the purpose which it serves—these all depend upon manifold relationships and do not affect the principle. Why it has been differentiated in different circumstances we shall have occasion to discuss later; for the moment it is enough that at the end of its migratory journey each Ruff occupies one position on the meeting ground. Now birds that are paired for life, whose food-supply is not affected by alternations of climate, have no occasion to desert the locality wherein they have reared their offspring, and so their movements, being subject to a routine which would tend to become increasingly definite, must in the course of time and accord- ing to the law of habit formation become organised into the behaviour we observe. Is it necessary, therefore, to seek an explanation of their tendency to remain in one place in any- thing so complex as an inherited disposition ¢ Again, since we have to confess to so very much ignorance on so many points connected with the whole phenomenon of migration, may there not be some condition, hitherto shrouded in mystery, which might place so different a complexion on the corresponding aspect of migrant behaviour as to rid us, in their case also, of the necessity of appealing to an inherited disposition? Such questions are justifiable. And if the life- E 2 56 DISPOSITION TO SECURE A TERRITORY histories of other species gave no further support to our interpretation, if, in short, the evidence were to break down at this point, then we should be forced to seek some other explana- tion more in keeping with the general body of facts. But far from placing any obstacle in the way of an interpretation in terms of inherited disposi- tion, the behaviour of many of those residents which are not paired for life gives us even surer ground for that belief. Moreover in their case the initial stages in the process are more acces- sible to observation. I will endeavour to explain why. In the process of reproduction the environment has its part to play—whether in the manner here suggested, or indirectly through the question of food-supply, matters not at the moment. Now, migratory species are more highly specialised than resident species as regards food, and are affected more by variations of temperature, so that they can live for only a part of the year in the countries which they visit for the purpose of procreation. Hence the organic changes, which set the whole process in motion, must be coincident in time with the growth of appropriate conditions in the environ- ment; for if it were not so, if the internal organic changes were to develop prematurely, the bird would ‘undertake its journey only to find an insufficiency of food upon its arrival, and this would scarcely contribute towards survival. Definite limitations have therefore been imposed upon the period of organic change. But in the ISOLATION OF THE MALE 57 case of many resident species the conditions are somewhat different, for they remain in the same locality throughout the year, and a gradual unfolding of the reproductive process cannot therefore have a similarly harmful effect. Thus it comes about that the behaviour of the migrant, when it arrives at the breeding ground and first falls under observation, represents a stage in the process which, in the case of the resident, is only reached by slow degrees ; and by closely observing the behaviour as it is presented to us in the life of the resident male, we not only gain a better imsight into the changes in operation, but can actually witness the breaking down of the winter routine, stereo- typed through repetition, by the new disposition as it arises. The first visible manifestations, even though they may be characterised by a certain amount of vagueness, are therefore of great importance if the behaviour is to be interpreted aright; and in order to insure that none of these earlier symptoms shall be missed, it is necessary to begin the daily record of the bird’s movements at an early date in the season. As a rule the second week in February is sufficiently early for the purpose, but the date varies according to the prevailing climatic conditions. Even in species widely remote there is great similarity of pro- cedure, and the behaviour of the Buntings is typical of that of many. With the rise of the appropriate organic state the male resorts at daybreak to a suitable environment, occupies a 58 DISPOSITION TO SECURE A TERRITORY definite position, and singling out some tree or prominent bush, which will serve as a head- quarters, advertises its presence there by song. At first the bird restricts its visits, which though frequent in occurrence are of short duration, for the most part to the early hours of the morning ; it disappears as suddenly as it appeared, and one can trace its flight to the feeding grounds —a homestead or perhaps some newly sown field. But by degrees the impulse to seek the society of the flock grows less and less pro- nounced, the visits to the territory are more and more prolonged, and the occupation of it then becomes the outstanding feature of the bird’s existence. This in outline is the course of procedure as it appears to an external observer. But although much can be learnt from the lives of these smaller species, there is no gain- saying the fact that a great deal of patient observation is required, and the process is apt to become tedious. ‘There are others, however, which are more readily observed, whilst their life-histories afford just as clear an insight into the effect produced by the new disposition upon the developing situation ; and among these the Lapwing takes a prominent position, because it is plentiful and inhabits open ground where it is easily kept in view. There is a water meadow with which I am familiar, where large numbers resort annually for the purpose of procreation. Here they begin to arrive towards the end of February, <= ‘S161 avof oy ur ssutmdey Aq pardnooo sariozt110} dy] SuImoys MOpvaUt 19}VM ay} Jo urTg aad NP Sel Nl Yi ys] Cael acd, ; Reena UPD BU OO 477 7 ee oe: seer aera BOTs as U/ Le Vigne *. Peer pea Ye A ay 3109 (Cr Ae vi oe Yi 3 Z ARNE N Ng wK NN d 205 f Spoojy 0} 9/Q0IT7 0 fee iN a! YS WS NYY aN YOu VUO 07 Joa Fz 10 8°8% ayeos plaid I or 234 feet to one inch I 2808 Scale Se SKS ARSENE RSs Danone Se VR nel, Emery Walker Ltd. sc. Plan of the water meadow showing the territories occupied by Lapwings in the year 1916. [Between pages 58 and 59. ISOLATION OF THE MALE 59 and at first collect in a small flock at one end of the meadow. A male, here and there, can then be seen to break away from the flock, and to establish itself in a definite position upon the unoccupied portion of the ground, where it remains isolated from its companions. Others do likewise until the greater part of the meadow is divided into territories. Six of these terri- tories I kept under observation for approximately two months in the year 1915. The occupant of the one marked No. 6 upon the 1915 plan was a lame bird, a fortunate occurrence as it enabled me to follow its movements with some accuracy ; and though it maintained its position for some weeks, it ultimately disappeared, as a result, I believe, of the persistent attacks of neighbouring males. The behaviour of the males during the first fortnight or so after they broke away from the flock was interesting. Though they retired to their territories and remained in them for the greater part of their time, yet it was only by degrees that they finally severed their connection with the flock, for so long as a nucleus of a flock remained, so long were they liable to desert their territories temporarily and to rejoin their companions. Lapwings, as is well known, collect in flocks during the winter months, and these flocks, which sometimes reach vast proportions, are to be found on tidal estuaries, water meadows, arable land, and such like places, according to the prevailing climatic conditions. ‘This flocking 60 DISPOSITION TO SECURE A TERRITORY may contribute towards survival, and may therefore be the result of congenital disposi- tions which have been determined on biological grounds. On the other hand, since food at that season is only to be obtained in a limited number of situations, the birds may be simply drawn together by accident. In the former case the behaviour would be instinctive, in the latter, though accidental at first, recurrent repetition would tend to make it habitual; but in either case the impulse to accompany the flock must be a powerful one, for on the one hand it would depend upon inherited, and on the other hand upon acquired, connections in the nervous system. Now observe that soon after the flock arrived in the meadow, single males detached themselves; there was no hesitation, they just retired from their com- panions and settled in their respective territories. They were not expelled, for if their leaving had been compulsory much commotion would have preceded their departure, and their return would certainly not have been welcomed. A reference to the plan will make the position clearer; the neutral zone inhabited by the flock is there shown as situated in one corner of the meadow, the territories that fell under observation are plotted out as far as possible to scale, and the more important zones of conflict are also marked. The males spent part of their time in their respective territories and part with the flock, so long as it remained in existence. When a ISOLATION OF THE MALE 61 male was in its territory it avoided companions and was openly hostile to intruders; when it was with the flock it wandered about with companions in search of food. The contrast between the two modes of behaviour was very marked, and it was evident that the gregarious instinct was gradually yielding its position of importance to the new factor—the territory. If there had been no flock, if a few solitary individuals had appeared here and there and had established themselves in different parts of the meadow, one would have had no definite evidence of the strength of the impulse in the male to seek a position of its own, one could only have argued from the general fact of males flocking in the winter and isolating themselves in spring that something more than accident was required to explain so radical a change. But since the birds returned in a flock to the ground upon which they intended to breed, and since the flock occupied temporarily part of the ground whilst the partitioning of the remainder was still proceeding, it was possible to gauge the strength of the impulse, which was forcing the males to isolate themselves in particular areas of ground, by comparing it with the impulse to accompany the flock—and the measure of its intensity was the rapidity with which the latter impulse yielded its position of importance. Like the Lapwing, the Coot and Moor-Hen are easily kept under observation, and since many individuals often breed in proximity, 62 DISPOSITION TO SECURE A TERRITORY more than one can be watched at the same moment; moreover the area occupied by each male generally embraces an open piece of water as well as part of the fringe of reeds, so that the movements of the bird can be followed without much difficulty. Under favour- able conditions manifestations of the developing situation become visible at a comparatively early date in the season—the middle or the latter part of February —and these manifes- tations resemble those of other species. But the Moor-Hen passes summer and winter alike in the same situation, and being therefore in a position to respond at once to internal stimu- lation, however vague, the change from the one state to the other is gradual. This, however, is a matter of detail; the main consideration lies in the fact that the impulse to retire to a definite position, to avoid companions, and to live in seclusion, is strongly marked, and produces a type of behaviour similar on the whole to that of the Lapwing. First of all there is the appropriation of a certain position, the limits of which are fixed according to the law of habit formation, and according to the pressure exerted by neighbouring individuals ; then there is the neutral ground over which the birds wander amicably in search of food; and finally there is the contrast between the pugnacity of the male whilst in its territory, and its comparative friendliness when upon neutral ground. Evidence of similar behaviour is to be found ISOLATION OF THE MALE 63 in the life of the Black Grouse, a bird which has always excited the curiosity of naturalists on account of the special meeting places to which both sexes resort in the spring. Mr Edmund Selous watched these birds in Scandinavia, where he kept a daily record at one of the meeting places. In various passages he refers to the appropriation of particular positions by particular males, and concludes thus: ‘ It would seem from this that, like the Ruffs, each male Blackeock has its particular domain on _ the assembly ground, though the size of this is in proportion to the much greater space of the whole. On the other mornings, too, the same birds, as I now make no doubt they are, have flown down into approximately the same areas.” The cliff-breeding species—Guillemots, Razor- bills, and Puffins—are difficult to investigate because individuals vary so little, and the sexes resemble one another so closely; yet, despite these difficulties, we can gain some idea of the general purport of their activities. But when the ledges are crowded and the air is filled with countless multitudes, how is it possible to keep a single bird in view for a sufficient length of time to understand its routine? The difficulty is not an insuperable one. The flights, under- taken seemingly for no particular purpose, are often of short duration and are completed before the strain of observation becomes too great ; moreover an individual sometimes possesses a special mark or characteristic which serves to 64 DISPOSITION TO SECURE A TERRITORY make it conspicuous. For example, there is a well-marked variety of the Common Guillemot, the Ringed or Bridled Guillemot of science, distinguished by an unusual development of white round the eye and along the furrow behind it. One such individual I was fortunate in discovering upon a crowded cliff, and, as in the case of the Lapwing with the broken leg or the Yellow Bunting with the injured foot, the identity of the bird was beyond dis- pute, and one could observe that it appropriated to itself a particular position upon a particular ledge. Guillemots and Razorbills return at intervals - to the breeding stations early in the season, and these visits are repeated with growing frequency until the birds are finally established. I have witnessed these periodic returns during March in the south of England, and during April in the north-west of Ireland, and I am informed that in the latter district such visits may occur as early as February. Giitke, who had ample opportunity of observing the birds in Heligoland, puts their return at an even earlier date. ‘They visit their breeding places,” he says, “in flocks of thousands at the New Year, often even as early as December, as though they wanted to make sure of their former haunts being well preserved and ready for their reception.” Such visits, however, are irregular in occurrence; the birds arrive, and, after spending a short time upon the ledges, disappear. And since there is not the same evidence in their coming and going : a: re Ate | ae Hs ite ip iH ce h i PT A ae a bi a ek me ey i ISOLATION OF THE MALE 65 of that method which we observe in the periodical returns of the Bunting or the Finch, it may be thought that needless importance is being attached to an episode in their lives which is quite intelligible in terms of a feeble response determined by a dawning organic change. While it may be quite intelligible in such terms it is not thereby explained; for every response must have as its antecedent an inherited connection in the nervous system determined on biological grounds. Besides, these early periodic returns conform in general to the type of behaviour displayed by other species, the males of which return to their breed- ing grounds many weeks before the real business of reproduction begins. Are we then justified in regarding them as accidents of the developing situation? Are we not rather bound to admit that they have some definite biological end to serve ? These examples show that the males of many species reverse their mode of life at the com- mencement of the breeding season and proceed to isolate themselves, each one in a definitely delimited area. | There are three ways in which we may attempt to interpret this particular mode of male behaviour. We may regard it as an accidental circumstance, nowise influencing the course of subsequent procedure; or, appealing to the law of habit formation, we may regard it as an individual acquirement; or 66 DISPOSITION TO SECURE A TERRITORY again, we may invest it with a deeper sig- nificance and seek its origin in some specific congenital disposition determined on_ purely biological grounds. Which of these three shall we choose? The first by itself requires but little consideration ; for though it might explain the initial visit, it cannot account for the persistency with which the plot of ground is afterwards resorted to. Supposing, however, that we combine the first and the second; supposing, that is to say, we assume, for the purpose of argument, that the initial visit is fortuitous, and that constancy is supplied by habit formation—would that be a satisfactory interpretation? It is a simple one, inasmuch as it only requires that a male shall alight by chance in a particular place for a few mornings in succession in order that the process may be set in motion. Now an essential con- dition of habit formation is recurrent repetition ; given this repetition and, it is true, any mode of activity is liable to become firmly established. But how can we explain the repetition? Even if we are justified in assuming that the initial visit is purely an accidental occurrence, we cannot presume too far upon the laws of chance and assume that the repetition, at first, is also fortuitous. So that we come back to the congenital basis, the last of our three propositions. And it will, I think, be admitted that the facts give us some grounds for believing that the securing of the territory has its root in the inherited con- CONCLUSION 67 stitution of the bird. In comparing the behaviour of the migratory male with that of the resident, attention was drawn to the manner in which the occupation of a territory was effected: the former bird, it may be remembered, established itself without delay, whereas the latter did so only by degrees, and the difference was attributed to the incidence of migration which required a closer correspondence between organic process and external environment. But the significance for us just now lies in the fact that the definite- ness, which accompanies the initial behaviour of the migratory male in relation to the territory, cannot have been acquired by repetition; for this reason, that when the male occupies its space of ground at the end of its long and arduous journey, it does so without preparation or experiment, even without hesitation, as if aware that it was making good the first step in the process of reproduction. No doubt, if it happened to be an individual that had already experienced the enjoyment of reproduction, it might be aware of the immediate results to be achieved and act accordingly. But among the hosts of migrants that one observes, there must be many males which have not previously mated ; and yet, upon arrival, they all behave in a similarly definite manner—so that experience cannot well be the primary factor in the situa- tion. If, then, the essential condition of habit formation is absent and experience is eliminated, there is nothing left but racial preparation to fall back upon. F 68 DISPOSITION TO SECURE A TERRITORY Nevertheless, it is true that many resident males seem to pass through a period of indecision before they establish themselves permanently in their respective territories; they come and go, their visits grow more and more pro- longed, and only after the lapse of some considerable time does the process of establish- ment attain that degree of completeness which is represented in the initial behaviour of the migratory male. Their whole procedure seems therefore to bear the stamp of individual ac- quirement ; and, if it stood alone, we might be content to construe it thus, but the example of the migratory male necessitates our look- ing elsewhere for the real meaning of the indecision. Let me first of all give some instances of the persistence with which a male remains in one spot, and this despite the fact that it has no mate. A Reed-Bunting occupied a central territory in a strip of marshy ground inhabited annually by four or five males of this species. Through- out April, May, and until the 19th June, it clung to its small plot of ground, tolerated no intrusion, and sang incessantly. Two Whitethroats arrived at much the same time—the 30th April approximately—and occupied the corner of a small plantation ; the one obtained a mate the day following its arrival, the other remained unpaired for a fortnight. A Reed-Warbler established itself amongst CONCLUSION 69 some willows and alders adjoining a reed-bed and made its headquarters in a small willow bush. Not more than fifteen yards away, on the edge of the main portion of the reeds, another male was established and was paired on the 22nd May. Each morning the single male behaved in much the same way, singing continuously whilst perched upon the bush. And so the days passed by until it seemed improbable that it would ever secure a mate, but one appeared on the 20th June, and a nest was built forthwith. Now it is difficult to believe that a chance visit, even though repeated for a few mornings in succession, could have accounted for the Reed-Bunting remaining so persistently in the marsh, or the Whitethroat in one corner of the osier bed, or the Reed-Warbler in that one particular willow. Not only so, but if a habit of such evident strength can be acquired so readily, we have a right to ask why it should only be acquired in the spring—why not at every season ? Considerations such as these lead to the belief that there must be some congenital basis to account for such persistent endeavour; the more so since it is difficult not to be impressed with the conative aspect of the male’s behaviour. To a stranger, unacquainted with its previous history, the bird might appear to be leading a life of hesitation, whereas, if carefully watched, its whole attitude will be found to betray symptoms of a striving towards some end ; and the frequent departure and return, which might 70 DISPOSITION TO SECURE A TERRITORY be pointed to as the material from which a definite mode of procedure would be likely to emerge, is in reality behaviour of a determinate sort. My interpretation, then, of the apparent indecision in the behaviour of the resident male is this. During the winter most species live in societies, together they seek their food and together they retire in the evening to the accustomed roosting places; and the association of different individuals confers mutual benefits upon the associates. The movements of these societies are dominated by the question of food ; all else is subservient, and the supply of the necessary sustenance may, under certain con- ditions, become a difficulty which can only be met by energy and resource. After the long night the sensation of hunger is strong, and the birds, on awakening, fly to the accustomed feeding grounds, returning again in the evening to the selected spot, and by frequent repeti- tion a routine becomes established. Thus the behaviour of each individual is determined not only by the powerful gregarious impulse but also by the habits formed in connection therewith during many weeks in succession. Now with the rise of the appropriate organic state, the disposition to seek the breeding ground and there to establish itself becomes dominant in the male. But the process is a gradual one. There is no need, as happens amongst the migrants, for the period of organic change to conform rigidly to the growth of CONCLUSION 71 any particular condition in the environment, and hence for a time the bird oscillates between two modes of behaviour—between that one organised by frequent repetition and that one determined by the functioning of this new disposition. To look at the matter broadly, it is scarcely likely that so definite a mode of behaviour would recur with such regularity, generation after generation, in the individuals belonging to so many widely divergent forms, if it had no root in the inborn constitution of the bird. But the law of habit formation has its part to play also. By itself it is inadequate; yet it probably does assist very materially in adding still greater definition, and it probably is responsible in a large measure for determining the limits of the territory according to the conditions of existence of the species—thus the Falcon seeks its prey over wide tracts of land, and, by hunting over certain ground repeatedly, establishes a routine, which broadly fixes the area occupied; the Woodpecker cannot find food upon every tree, and every forest does not contain the necessary trees, and therefore the bird regulates its flight according to the position of the trees; and the Warbler, finding food close at hand, does not need to travel far, and the area it occupies is consequently small. So that the most likely solution of the problem will be found in a combination of our second and third propositions; that is to say, in F 2 72 DISPOSITION TO SECURE A TERRITORY an initial responsive behaviour provided for in the inherited constitution of the nervous system, and in a definiteness acquired by repetition and determined by relationships in the external environment. CHAPTER III THE DISPOSITION TO DEFEND THE TERRITORY In the previous chapter I endeavoured to show that each male establishes a territory at the commencement of the breeding season, and there isolates itself from members of its own sex. And further I gave my reasons for believing that this particular mode of behaviour is deter- mined by the inherited nature of the bird, and that we are justified in speaking of it as “a disposition to secure a territory” because we can perceive its prospective value. But the act of establishment is only one step towards “securing.” By itself it can achieve nothing ; for any number of different individuals might fix upon the same situation, and if there were nothing in the inherited constitution of the bird to prevent this happening, where would be the security, or how could any benefit accrue to the species ? In withdrawing from its companions in the spring, the male is breaking with the past, and this action marks a definite change in its routine of existence. But the change does not end in attempted isolation; it is carried farther and extends to the innermost life and affects what, 78 74 DISPOSITION 'TO DEFEND THE TERRITORY humanly speaking, we should term its emotional nature, so that the bird becomes openly hostile towards other males with whom previously it had lived on amicable terms. The seasonal organic condition is responsible for the functioning of the disposition which results in this intolerance, just as it is for the functioning of the disposition which leads to the establishment of the territory; and the effect of these two dispositions is that a space of ground is not only occupied but made secure from intrusion. The process is a simple one. There is no reason to believe, there is no necessity to believe, that any part of the pro- cedure is conditioned by anticipatory meaning ; the behaviour is “instinctive” in Professor Lloyd Morgan’s definition of the word, since it is of a “specific congenital type, dependent upon purely biological conditions, nowise guided by conscious experience though affording data for the life of consciousness.” That the males of many animals are apt to become quarrelsome during the mating period is notorious. Darwin collected a number of facts, many of which related to birds, showing the nature and extent of the strife when the sexual instinct dominated the situation. And pondering over these facts, he deduced therefrom a “law of battle,” which, he believed, bore a direct relation to the possession of a female. And it must be admitted that he had excellent ground for his conclusion in the fact not only that the conflicts occur mainly during the pairing season, but that / / 7 / / / 4 Yq SINLOYS 11g qoazoetep ayy JOU 7ittaq to wotssassod ayy of Pu Sein THE LAW OF BATTLE 75 the female is often a spectator and seems even to pair with the victor. I accepted it, therefore, as the most reasonable interpretation of the facts. But, as time passed by, incidents of a conflicting character led me to think that after all there might be another solution of the problem. And when it was no longer possible to doubt that there was a widespread tendency to establish territories, it at once became manifest that the battles might have an important part to play in the whole scheme. But how was this to be proved? What sort of evidence could show whether the proximate end for which the males were fighting had reference to the female or to the territory? Clearly nothing but a complete record of the whole series of events leading up to reproduction could supply the necessary data upon which a decision might rest. In the present chapter I shall give, in the first place, the reasons which lead me to think that the origin of the fighting cannot be traced to the female ; afterwards, the evidence which seems to show that it must be sought in the territory ; and finally, I shall make a suggestion as to the part the female may play in the whole scheme. The facts upon which the “law of battle was founded were ample to establish the truth of its main doctrine. But the evidence upon which the interpretation of the battles was based was somewhat superficial. It was based mainly upon the general observation that one or more females could frequently be observed to accompany the combatants ; and if this were the sole condition ” 76 DISPOSITION TO DEFEND THE TERRITORY under which the fighting occurred, one must admit that this view would have much to recommend it. But it is not merely a question of males disputing in the presence of a female; for males fight when no female is present, pair attacks pair, or a male may even attack a female —in fact there is a complexity of strife which is bewildering. In attributing the rivalry to the presence of the female, it is assumed that males are in a preponderance, and that consequently two or more are always ready to compete for a mate. Her presence is presumably the condition under which his pugnacious nature is rendered suscep- tible to its appropriate stimulus, the stimulus being, of course, supplied by the opponent. There would be nothing against this interpreta- tion if it were in accord with the facts; but it can, I think, be shown that the males are just as pugnacious and the conflicts just as severe even when the question of securing a mate is definitely excluded ; and I shall now give the evidence which has led me to this conclusion. In the previous chapter we had occasion to refer to the difference in the times of arrival of the male and female migrants, and we came to the conclusion, it may be remem- bered, that this was a fact of some import- ance, because it gave us a clue to the meaning of much that was otherwise obscure in their behaviour. But it is also of importance in connection with the particular aspect of the problem which we now have in view, for if it MENTAL IMAGE OF THE FEMALE 17 can be shown that males, when they first reach their breeding grounds, are even then intolerant of one another’s presence, if their actions and attitudes betray similar symptoms of quasi- conation, if disputes are rife and the struggles of a kind to preclude all doubt as to their reality, then it is manifest that in such cases their intolerance cannot be due to the presence of the female. Here, however, I must refer to a view which is held by some psychologists, namely, that amongst the higher animals, even on_ the occasion of the first performance of an instinc- tive act, there is some vague awareness of the proximate end to be attained. Discussing the nature of instincts, Dr M‘Dougall’ says, “Nor does our definition insist, as some do, that the instinctive action is performed without aware- ness of the end towards which it tends, for this, too, is not essential ; it may be, and in the case of the lower animals no doubt often is, so performed, as also by the very young child, but in the case of the higher animals some prevision of the immediate end, however vague, probably accompanies an instinctive action that has often been repeated.” A similar view seems to be held by Dr Stout.” ‘As I have already shown,” he says, “animals in their instinctive actions do actually behave from the outset as if they were continuously interested in the development of what is for them one and the same situation or course of events; they actually 1 Social Psychology. 2 Manual of Psychology. 78 DISPOSITION TO DEFEND THE TERRITORY behave as if they were continuously attentive, looking forward beyond the immediately present experience in preparation for what is to come. They apparently watch, wait, search, are on the alert. They also behave exactly as if they appreciated a difference between relative success and failure, trying again when a certain percep- tible result is not attained and varying their procedure in so far as it has been unsuccessful. All these characters are found in the first nest- building of birds as well as in the second; they are found also in courses of conduct which occur only once in the lifetime of the animal.” Both these writers would, I imagine, contend that, even when a female is absent, the idea of the female, as the end in view throughout, is present; and they would argue that the fact of her absence during the fighting in no way disposes of the belief that she is the condition under which the pugnacious instinct of the male is rendered usceptible to stimulation. What reason is there to think that this inter- pretation is ‘applicable to the case under con- sideration? When a female is present, we observe that the males are pugnacious, and, when she is absent, that they still continue to be hostile—that is to say, they behave as zf she were present. Now, as far as I can ascertain, the “as if” is the only ground there is for supposing that the female is represented in imaginal form—there is no evidence of the fact, if fact it be. On the contrary, the behaviour of the male affords some fairly conclusive evidence MENTAL IMAGE OF THE FEMALE 19 that no such image is the primary factor in exciting the instinctive reaction. For if it be the actual presence of the female, or, in the absence of such, a mental image, that renders the pugnacious nature of the male responsive ; provided the usual stimulus were present, the instinct ought surely to respond, not only under one particular circumstance, but under all circumstances. Yet, as we shall presently see, a male is by no means consistently intolerant of other males. It may be sociable at one moment or pugnacious at another, but the pugnacity is always peculiar to a certain occasion—the occupation of a territory. What shall we say then—that a mental image is a situational item only when the territory is occupied? It may be so; it may be that the fact of occupation gives rise to the mental image which, in its turn, renders the fighting instinct explosive, which again renders the possession of the territory secure. That such an inter- pretation is possible we must all admit. But if it were true, though it would not affect the main consideration, namely, whether the fighting has reference to the possession of a particular female, or to the protection of the territory, it would make further discussion as to which of these is the condition of the fighting unprofitable, for each would have its part to play in the process, the territory remaining, however, the principal factor in the situation. Now the difference in the times of arrival of the male and female migrant varies in 80 DISPOSITION TO DEFEND THE TERRITORY different species from a few days to a fortnight or even more. It is most marked in those that return to their breeding grounds early in the season, and the greater the margin of difference the greater scope is there for observation. In my records for the past twelve years, there are frequent references to these initial male contests in the life of the Willow-Warbler and of the Chiff- chaff; and in the district which I have in mind, these two species arrive early in the season, the males preceding the females by a week or even as much as a fortnight. Suppose, then, that two Chiffchaffs establish themselves in adjoining territories ; or suppose that a male settles in a territory already occupied; what is the result ? Well, scenes of hostility soon become apparent ; as the birds approach one another they become more and more restive, their song ceases, they no longer search for food in the usual methodical manner, but instead their movements are hurried and their call-notes are uttered rapidly—all of which betrays a heightened emotional tone. Then the climax is reached, there is a momentary fluttering of tiny wings, a clicking of bills, and for the time being that may be all. But unless one or other of the combatants retires, this scene may be repeated many times in the course of a few hours, and repeated with varying degrees of severity. Yet the fighting, even in the most extreme form, when the birds locked together fall slowly to the ground, is seldom of an impressive kind, and one has to bear in mind the capabilities of the actors, remembering that ABSENCE OF THE FEMALE 81 the most severe struggle might readily be inter- preted as a game if it were not for certain symptoms which reveal its inner nature. The males of many other migrants can fre- quently be observed to fight when there was every reason to believe that females had still to arrive. The Blackcap is notoriously pug- nacious, but not more so than the Marsh-W arbler or the Whinchat. Here in Worcestershire, the Arundo phragmites grows mainly on certain sheets of water which are comparatively few and far between, and the Reed-Warbler is consequently restricted to isolated and more or less confined areas. The males arrive early in May before the new growth of reeds has attained any considerable height, and each one has its own position in the reed-bed, sings there, and throughout the whole period of reproduction actively resists intrusion on the part of other males. I have kept watch upon a small area of reeds daily from the date of the first arrival ; each individual was known to me, and as the growing reeds were only a few inches in height, a female could scarcely have escaped detection. Yet time and again disputes arose, and males pursued and pecked one another, striving to attain that isolation for which racial preparation had fitted them. But on account of their violence, or their novelty, or because the absence of a female was beyond question, some battles stand out in one’s memory more prominently than others. An instance of this was a struggle between two 82 DISPOSITION TO DEFEND THE TERRITORY Whitethroats which happened in the latter part of April and lasted for three successive days. The scene of its occurrence was more or less the same on each occasion, and the area over which the birds wandered was comparatively small. The fighting was characterised by persistent effort and was of a most determined kind, and so engrossed did the assailants become that they even fluttered to the ground at my feet. No trace of a female was to be seen at any time during these three days, nor, during the pauses in the conflict, was the emotional behaviour of a kind which led me to suppose that a female was anywhere in the vicinity. And, if she had been near, she must have made her presence known, for the belief that she is a timid creature, | skulking on such occasions in the undergrowth, is by no means borne out by experience. Even more impressive was a battle between two male Cuckoos. It occurred high up in the air above the tops of some tall elm-trees which roughly marked the boundary line between their respective areas, and the actions of the birds were plainly visible. At the moment of actual collision the opponents were generally in a vertical position, and wings, feet, and beaks were made use of in turn; one could plainly see them strike at one another with their feet, and one could observe the open bill which generally denotes exhaustion, but may of course have been due to anger, or used as a means of producing terror. Yet no female appeared in the locality until six days after the occurrence of this struggle—and / j = / e ? iE 5 } ps f 2 ry / , j Male Cuckoos figiiing before he arrival of a female / ABSENCE OF THE FEMALE 83 she certainly is not easily overlooked, for her note is unmistakable even when the behaviour of the male does not betray her arrival. That the actual presence of the respective females exercised any influence on the course of these struggles is more than doubtful. Not only did one fail to detect them, but one’s failure to do so was confirmed by the knowledge that they had not yet arrived in those particular localities. Hence the fact of the male preceding the female is a valuable aid to the interpretation of subse- quent behaviour; and one appreciates it the more after having experienced the difficulty of deciding whether she is present during the conflicts between resident males, for no matter how carefully we may observe the conditions which lead up to, and which accompany, such conflicts, or how closely we may scrutinise the surrounding trees, undergrowth, or ground, there always remains the possibility that she may, after all, have been overlooked. But this must not be taken to imply that in such cases direct observation alone can lead to no serviceable result, or that the evidence gained therefrom is worthless. Far from it. Failure to detect a female is so very common an occurrence that, even if we lacked the corroborative evidence supplied in the life of the migratory male, it would still be unreasonable to suppose that it were solely due to mistaken observation. We mark her absence during the conflicts between the respective males of many common species— the Finches, Buntings, and Thrushes that occupy G 84 DISPOSITION TO DEFEND THE TERRITORY their territories early in the season when the hedgerows and trees are still bare; but more fre- quently amongst those that inhabit open ground, because the movements of the birds are there more accessible to observation. For instance, half a dozen or more Lapwings can be kept in view at the same time, and as they stand at dawn in solitary state, keeping watch upon their respec- tive territories, they are conspicuous objects on the short, frosted grass ; no stranger can enter the arena without the observer being aware of it, no commotion can occur but one detects it, no movement however small need be missed. And so they fight, in a manner which leaves no doubt as to the reality of the struggle, when their prospective mates are absent not only from the particular territories in which the conflicts take place, but absent too from those adjoining. If the fact that males fight before they are paired and in the absence of a female could be placed beyond all question, it would no longer be possible to regard her possession as the end for which they are contending, and consequently there would be no need to produce further evidence. But the examples which I have given refer, of course, to only a few migrants and a few residents—and moreover it must be admitted that a female is often conspicuous during the battles — so that by themselves they must be regarded, and rightly so, as inconclusive. We must therefore pass on to consider evidence of a somewhat different character. I spoke of the complexity of the strife. By COMPLEXITY OF THE FIGHTING 85 this I mean that it is not merely a matter of disputes between adjoining males, but that it is a far more comprehensive business involving both sexes. ‘Thus female fights with female and pair with pair, or a male will attack a female, or, again, a pair will combine against a single male or a single female. And from all this com- plexity of strife we gain much valuable evidence in regard to the question immediately before us. For when one pair attacks another, or males that are definitely paired fight with one another, or an unpaired male attacks either sex of a neighbouring pair indiscriminately, there is surely little ground for supposing that the possession of a mate is the reason of it all. The battles between pairs of the same species are by no means uncommon. Observe, for example, the central pair of three pairs of Reed- Buntings occupying adjoining territories, and keep a daily record of the routine of activity practised by both sexes during the early hours of the morning ; then, at the close of the season, summarise all the fighting under different head- ings, and it will be found that the number of occasions upon which the central pair attacked, or was attacked by, neighbouring pairs will form a considerable portion of the whole. Or watch the Moor-Hen, and for the purpose choose some sheet of water large enough to accommodate three or more pairs, and so situated that the birds can always be kept in view. Karly in February the pool will be haunted by numbers of individuals of both sexes, all 86 DISPOSITION TO DEFEND THE TERRITORY swimming about together, and, if the pool is surrounded by arable land, wandering over that land subject to no territorial restrictions, appar- ently free to seek food where they will. But as time goes by, their number gradually decreases until a few pairs only remain, and these will occupy definite areas. If careful watch is then kept and the relations of the pairs closely studied, there will be no difficulty in observing the particular kind of warfare to which I am alluding, and it will be noticed that the encounters are of a particularly violent descrip- tion. Thus two pairs approach one another, and, when they meet, throw themselves upon their backs, each bird striking at its adversary with its feet or seizing hold of it with its beak ; and though, in the commotion that ensues, it is almost impossible to determine what exactly is happening, there is reason to believe that the sexes attack one another indiscriminately. A struggle between two pairs of Pied Wag- tails is worth mentioning. It impressed itself upon my memory because of the unusual vigour with which it was conducted. ‘The battle lasted for fifteen minutes or more, and the four birds, collecting together, pursued and attacked one another—at one moment in the air, at another upon the reof of a house where they would alight and flutter about on the slates, uttering their call-note without ceasing—until finally they disappeared from view, still, however, con- tinuing the struggle. Such is the nature of the warfare which COMPLEXITY OF THE FIGHTING 87 prevails between neighbouring pairs, and which can be observed in the life of many other species—the Chaffinch, Stonechat, Blackbird, Partridge, Jay, to mention but a few. 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 sex of a neighbouring pair indis- criminately, 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 prob- ably 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 speak- ing 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 G2 88 DISPOSITION TO DEFEND THE TERRITORY 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 sexes are mixed up in the fighting— it cannot, for instance, explain the fact that an unpaired male will attack either sex 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 sexual function has ceased, and the female is engaged in incuba- tion 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 sexually 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 sexes participate in the fighting, and that individuals of the opposite sex fre- quently 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 sexual instinct is COMPLEXITY OF THE FIGHTING 89 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 situa- tion, then there would be no need to probe the matter deeper, there would be no reason to doubt the assertion that the quarrel had direct reference to the female. But assuredly 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 sex to gain or keep possession of one of the other sex. So that taking all these facts into consideration, we are 90 DISPOSITION TO DEFEND THE TERRITORY 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 mot merely a. question of — “battle; or sor ‘‘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 associated with the disposition which is manifested in the isolation of the male from its companions, and forms there- with an imperium im 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 con- dition of the fighting, it is difficult to find just the sort of evidence that is required. Neverthe- less, 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 FIGHTING CONTROLLED 91 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 succumbed 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 sexual 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 remark- ably 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 92 DISPOSITION TO DEFEND THE TERRITORY air, and sometimes even on the ground, and fighting thus they gradually approach and pass beyond the limits of the territory. Where- upon 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 sexual 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 gradu- ally 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 FIGHTING CONTROLLED 93 territories are still in process of being established, and definiteness has still to be acquired, tres- passing 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 sex, 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 attitude 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 circum- stances which lead up to the quarrels and the circumstances under which such quarrels come to an end, we shall find, when we have accumu- lated a sufficient body of observations, that the disputes always originate in trespass, and that hostilities always cease when the _ trespasser 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. y . t ‘ BIRDS OF PREY AND THE RAVEN - 217 though no collision may actually take place, yet the fact that the Raven, when it turns to face its adversary, is obliged to drop the stick which it carries, is not only an indication of the character of the struggle, but it shows that a definite end is gained—that the efforts of the Raven to build in that particular locality are hampered. But the Falcon is not the only enemy that the Raven has to face; Buzzards are just as intolerant of the presence of Ravens in their neighbourhood as the Ravens are of them, and consequently there is incessant quarrelling wherever the same _ locality is inhabited. As a rule, the fighting occurs whilst the birds are on the wing; the Buzzard rises to a considerable height, and, closing its wings, stoops at the Raven below, and when within a short distance of its adversary, swerves upwards and gains a position from which it can again attack. The Buzzard, however, is by no means always the aggressor; I have watched one so persistently harassed by a Raven that at length it left the rock upon which it was resting and disappeared from view, still followed by its rival. Thus it seems as if they were evenly matched, and, when they occupy the same locality, it is interesting to notice how the initiative passes from the one to the other according to the position occupied by the birds in their respective territories. That there is constant warfare between the Green Woodpecker and the Starling is well known, the purpose of the Starling being to 218 WARFARE BETWEEN DIFFERENT SPECIES gain possession of the hole which the Wood- pecker with much skill has drilled for itself. As far as my experience goes, the Starling is always the aggressor, and there is only too good reason to fear that, in the course of time, the Green Woodpecker will disappear as a result of the greater fertility and tenacity of its enemy. The Martin suffers a similar kind of persecution from the House-Sparrow, and here again there is reason to believe that the greater virility of the Sparrow will hasten the extinction of its rival. In cases of this description the purpose of the fighting is clear, and one can understand why such divergent species should be hostile to one another; yet others, equally remote in the scale of nature, are hostile when no_ such ostensible reason can be assigned for their hostility. Few birds are more pugnacious than the Moor-Hen, and the determined manner in which different individuals fight with one another is notorious. But the intolerance it displays towards other species is no less remark- able, and its pugnacious instinct seems to be peculiarly susceptible to stimulation by different individuals belonging to widely divergent forms. At one moment a Lapwing may be attacked, at another a Thrush or a Starling, harmless strangers that have approached the pool to drink ; even a Water-Rail, as it threads its way through the rushes, may fail to escape detec- tion ; and, which is still more curious, a covey of Partridges will evoke response if they approach the pool too closely. LAPWINGS AND SNIPE 219 Here is a curious instance of apparent waste of energy. A pair of Magpies built their nest in an ilex tree. Early one morning there was a commotion in the tree, much flapping of wings and a medley of sounds which told of large birds engaged in a struggle—the Magpies were attacking a pair of Wood-Pigeons. ‘There was no question as to the genuineness of the struggle, nor any doubt as to the proximate end for which the Magpies were striving, for their efforts continued so long as the Wood-Pigeons remained in the tree, and only ceased when they had succeeded in driving them away. Turning next to species which are less distantly related, we find that instances of intolerance are more numerous and that a wider range of species is involved. The hostility that the Lapwing displays towards the Snipe calls for special remark. It often happens that the marshes or water meadows, that are such favourite haunts of the Lapwing, are also resorted to by Snipe for the purpose of securing food, or it may be even for the purpose of reproduction. In such places both species are often abundant ; the meadow is divided up into Lapwings’ territories, and early in the season the Snipe wander over it in small parties, singly, or in pairs. Now, if it were only on isolated occasions that the Lapwing paid heed to the Snipe, one would not perhaps attach any peculiar significance to the fact; but the pugnacious instinct of the bird responds to the presence of this intruder almost as freely as it 220 WARFARE BETWEEN DIFFERENT SPECIES does to that of another Lapwing. Again and again, day after day, the Snipe are attacked and driven off in a manner which would be fittingly described as persistent persecution, for the Snipe has neither the physical capacity nor apparently any instinctive tendency to retaliate. Thus a Lapwing may come suddenly upon a small party of Snipe hidden from view in a dyke where they are probing the ground for food; the Snipe immediately rise and fly away and there is momentary confusion as the Lapwing darts first at this one, then at that; or, espying a Snipe at rest at the opposite end of its territory, it will first of all run rapidly towards it, and then fly after it, as, with twisting flight, it darts hither and thither a few feet above the ground; or again, it will attack and rapidly pursue solitary individuals as they skim across its territory and attempt to settle. Is this intolerance merely an exuberant expression of an instinct which is serviceable in another direction? The behaviour of the Lapwing scarcely justifies such a conclusion, for all its actions denote a striving towards some end which we can describe, and it seems to gain satisfaction only when the ejection of the intruder has been accomplished. Many of the Warblers display irritation when approached by other birds which we should scarcely expect would arouse their hostility. The Hedge-Sparrow, for example, is frequently regarded with suspicion, and it is by no means unusual to see it attacked by so TITS AND WARBLERS 221 small a bird as the Chiffchaff. The Wood- Warbler is also pugnacious, and will even attack a pair of Chaffinches. Between the Tit family and some of the smaller Warblers there are constant exhibitions of hostility ; even the Great Tit is liable to be driven away, but the Blue Tit is especially marked out for persecution, though doubtless it is well able to hold its own. The following incident will show how real is the antagonism between these two families. A Chiffchaff occupied the corner of a small osier bed, and was particularly aggressive towards other closely-related forms in_ its immediate neighbourhood. On two mornings in succession ten Blue Tits invaded its ground, passing from end to end of it as they wended their way from tree to tree in search of food. Their presence evoked the usual hostile response, yet, withal, aroused the fear of the Chiffchaff, which, at times, appeared to be swayed by conflicting impulses. Now, in attempting to interpret the nature of the instinct which was evoked, one has to be guided, in a case of this description, by the similarity of the response to that which can be observed on other occasions and in other situations when the intention of the bird is clear. And on this occasion the Chiffchaff betrayed all the symptoms which normally precede an attack; it spread its tail, quivered its wings, uttered its high-pitched note rapidly, hopped from twig to twig, or flew restlessly from tree to tree, and seemed to be prevented from attacking only by the number 222 WARFARE BETWEEN DIFFERENT SPECIES of its opponents. ‘This, indeed, was shown by its subsequent behaviour, for whenever a Tit became temporarily detached from its com- panions it hesitated no longer but forthwith attacked. There are other species which are no less aggressive than the Warblers—the Chats for example. ‘The Stonechat regards with suspicion almost any bird of its own size, and will even pursue a Tree-Pipit if it approaches too closely. The same is true of the Whinchat, and one would scarcely expect to find this bird attacking Buntings as it sometimes does. A Whinchat that occupied some marshy ground was con- stantly at war with a pair of Reed-Buntings ; their territories were adjacent and in some measure overlapped, and the Whinchat drove away either sex indiscriminately, and was not only always the aggressor but seemed to be master of the situation. Coming now to kindred forms, those, that is to say, which belong to the same family, we find that, both in intensity and extent, the warfare far exceeds anything that we have thus far considered. So frequent, indeed, are acts of intolerance, and so readily awakened into activity is the pugnacious nature of the bird, that the fighting will almost bear comparison in volume with that which occurs between individuals of the same species. Between the Thrush and the Blackbird there are incessant quarrels early in the year, and the initiative seems to pass from one to the other according to WARBLERS 223 the circumstances in which they are placed. If the territory of a Thrush is invaded the Thrush is the aggressor, and, conversely, if that of the Blackbird is threatened, the Blackbird becomes the ageressor ; and so, when the territories of the two birds are adjacent or overlap, as frequently they do, there is constant friction, resulting in quarrels which attract attention on account of the noisiness of the birds. All the Warblers are exceedingly pugnacious, the fighting being especially severe between those that are very closely related. The Black- cap and the Garden- Warbler are constant rivals, and the scenes which can be witnessed when the two meet in competition are interesting from many points of view. The birds not only pursue and fight with one another, but their emotional behaviour reaches a high level of intensity—excitable outbursts of song are in- dulged in, tails are outspread, wings are slowly flapped, and feathers raised— in fact the attitudes assumed are similar in all respects to those which occur during the contests which are so frequent between the respective individuals of each species; and it would be difficult to point to any one item of behaviour which is not also manifest at one time or another during the battles between these rivals, and still more difficult to trace any difference in the intensity of the excitement. And if we are satisfied that the fighting in the one case is purposive, so, too, must we regard it as having some biological purpose to serve in the other. But the Garden- 224 WARFARE BETWEEN DIFFERENT SPECIES Warbler is not the only bird that acts as a stimulus to the instinct of the Blackcap; Whitethroats are often attacked, and the Chiff- chaff is a source of irritation. Even when a male Blackcap is engaged in incubation, it will leave its nest on the approach of a Chiffchaff, and, having driven away the intruder, proceed to sing excitedly. At other times both male and female will combine to attack this small intruder. But this does not mean that the Chiffchaff suffers persecution ; it is itself most aggressive, as is shown by the fact that it will join in the Blackcap quarrels and attack the combatants indiscriminately. Its behaviour, however, re- quires further consideration, especially as regards its relations with its nearest of kin—the Willow- Warbler; for here we have a mutual intolerance which is somewhat remarkable, and evidence of it can be found wherever the birds occupy the same ground. Now it can be observed that the hostility is not limited merely to occasional acts of intolerance, but that there is organised warfare lasting, it may be, for many days in succession, and that the actions of the birds bear the stamp of a persistent striving towards some end. On one occasion the Willow-Warbler may be the aggressor, on another the Chiff- chaff, and at times it is difficult to say which of the two is responsible for the quarrel. In size and in strength they are equal, and the “will to fight” is as strong in the one as in the other, so that it is seldom, if ever, possible to point to WARBLERS 225 this one as the victor and that one as the vanquished. Success or failure probably depends more upon the cumulative effect of many combats entailing physical exhaustion, than upon the issue of any one particular battle ; and whilst observation might quite well fail to distinguish any resultant change in the relative positions of the birds, or any harmful effect upon their constitutions, yet the area occupied by this one might be sufficiently curtailed to prejudice the welfare of the young, or the vitality of that one might be seriously impaired —and we should be none the wiser. Neither the Marsh-Warbler nor the Reed- Warbler will tolerate strangers within the small space of ground over which they exercise dominion. Of the two, the Marsh-Warbler is perhaps the more pugnacious, and will attack any other Warbler that approaches too closely ; Whitethroats are often pursued and driven away, and less frequently, Garden-Warblers. In one case, a male occupied the same ground as a Sedge-Warbler, and there was a constant feud between them; a willow-tree formed its headquarters, and this same tree seemed to be the headquarters of the Sedge-Warbler, so that they often met and whenever they did so they quarrelled. As a rule the Marsh-Warbler was the aggressor and had the mastery over its opponent, and when it attacked, it uttered a peculiar harsh scolding note, raised the feathers on its back, spread out its wings, and betrayed the usual symptoms of emotional excitement. 226 WARFARE BETWEEN DIFFERENT SPECIES On the other hand, the Sedge-Warbler is most aggressive towards other kindred species, and when a male happens to occupy the same ground as a Reed-Warbler, there are frequent battles between them and incessant commotion ; they fly at one another and meet in the air with | an audible clicking of bills, or pursue one another amongst the reeds, each one uttering its characteristic scolding note. The Tits, as a family, are notoriously pugnacious. I have seen a pair of Blue Tits attack a single Long-tailed ‘Tit with great determination, and not only did they pursue it, but, flying at it, struck it with considerable force. In giving an account of the domestic economy of the Carrion-Crow, Mr Edmund Selous refers to the hostility between this bird and the Magpie. “About a week ago,” he says,’ “I saw a Crow busily engaged in chasing away several Magpies, not only from three or four tall slender trees close together, in one of which it had its nest, but also from various other trees, not far off, round about. In this the Crow had a good deal of trouble, as the Magpies were always returning. After a time it was joined by another crow, which however did not take so active a part in the drama, nor did I see either of the two actually go to the nest, though I could only explain their action by supposing it was their own. This morning I saw the same thing reversed, for a pair of 1 Zoologist, 1912, p. 327. ROOKS AND CROWS 227 Magpies, with an undoubted nest, kept attacking a Crow that insisted on settling in one of a row of trees—also tall and slender—in which it was placed. Both were equally persevering—the Crow, though often chased away, always returning, and settling generally in the last tree of the row, where he would be left alone sometimes for a minute or two, but before long one of the Magpies flew at him, and put him to flight. The Crow defended itself, but not, it would seem, very successfully, and in the last attack upon him, made, with great spirit, in the air, a large black feather floated to the ground, which I made no doubt was his. Yet this did not drive him from the trees, and it was only on my approaching nearer that he finally left them. Thus we see that both species look upon the approach of the other to within a moderate distance of their nest as an intrusion.” That the Rook suffers persecution from the Carrion-Crow is a_ well-established fact, and there is reason to believe that it has another dangerous enemy in the Hooded Crow. According to the late Mr Ussher, Choughs will attack both Hooded Crows and Ravens. “I once saw,” he says, “two Choughs energetically attacking a pair of Ravens; they shot up into the air and darted down on the latter, whose heavy flight made them helpless against their agile tormentors.” Birds of prey are often hostile to one another. The Merlin is exceptionally pugnacious, and its boldness in attacking intruders is well known. Q 228 WARFARE BETWEEN DIFFERENT SPECIES When, for example, a Kestrel approaches its territory, it leaves the tree, bush, or rock upon which it was resting, utters its characteristic cry, and soars rapidly upwards; then, rising to a considerable height, it swoops down upon the Kestrel, and by alternately stooping at and chasing its opponent, drives it away from the immediate neighbourhood. What we have, then, to consider is, Do these battles between different species contribute towards the attainment of the end for which the whole territorial system has been evolved ? Let us take the individual and see whether we can establish any relation between the hostility it displays towards members of other species and its general disposition to secure a territory. We must remember that a male can have no knowledge of the prospective value of its behaviour, nor is it likely that it has any ulterior purpose in ejecting other males, beyond the pleasure it derives from satisfying its impulse to do so. The proximate end of its behaviour is to attack, nothing more, and this, of course, it can only do just in so far as the intruder evokes the appropriate instinct. Now the arguments we shall employ will, on the whole, be similar to those which we made use of in the second chapter, wherein we attempted to ascertain the conditions under which a male becomes intolerant of other males of its own species, and examined more especially the claims of the “territory” as opposed to those of the “female.” But here SEASONAL CHANGE OF RELATIONSHIP 229 we start on firmer ground, because the one factor which introduced an element of uncer- tainty—the female—can be definitely excluded ; at least it seems so to me, for granting even that her presence is the condition under which the pugnacious nature of the male is rendered susceptible to stimulation, it is difficult to see why a male of a different species should supply that stimulus, or what biological purpose could be served by its doing so. When dealing with the attitude of a male towards others of its kind, we attached consider- able significance to the fact that its pugnacious nature gained or lost susceptibility according to the position which it happened to occupy. We found, it will be remembered, that the same bird that was pugnacious in its own territory took no further interest in its opponent when the boundary was passed; and, moreover, that if it happened to wander into an adjoining one, it made no real effort to defend itself when attacked, but returned forthwith to its own headquarters. It remains to be shown whether the rivalry between different kinds of birds is similarly related to the position which the opponents happen to occupy at the time. First, then, there is the general consideration, namely, that the enmity occurs for the most part just at the time when the territories are in process of being established. During autumn and winter, many birds of more or less close affinity assemble together in flocks, wherever the supply of food is abundant, and are then 230 WARFARE BETWEEN DIFFERENT SPECIES not only sociable, but, so there is reason to believe, are mutually helpful both in discovering the necessary means of subsistence which are often none too plentiful, and in affording pro- tection from enemies, which, on the contrary, are often numerous. That the different units of which these flocks are composed should live on amicable terms is therefore as necessary for the welfare of the whole community at this particular season as that the different individuals of the same species should do so. But just as the sociable relations, which obtain between these individuals throughout the winter, undergo a marked change at the commencement of the breeding season, so, too, do different species, which habitually associate together, suddenly become hostile to one another. This change is coincident in time with the rise of the organic condition which leads to the establishment of territories; and the hostility continues, though in_ diminishing degree, throughout the breeding season, and dies away the following autumn. For example, different Warblers resort to the elders (Sambucus nigra) in September, and there pass much time feeding on the fruit which is then ripe and often abundant. In the same bush there may be Blackcaps, Garden-W arblers, Whitethroats, and Lesser Whitethroats, some preening their feathers, others searching for the berries, others again, with feathers relaxed, making feeble attempts to sing. Occasionally there may be a_ scufHle, perhaps between a SEASONAL CHANGE OF RELATIONSHIP 231 Blackeap and a Lesser Whitethroat, or between a Garden-Warbler and a Blackcap, but it is of short duration and lacks vigour. Apart, however, from such temporary disturbances, there is no real rupture in their relations, and certainly nothing to lead one to suppose that the bickerings are determined by the functioning of any specific instinct. Yet only a few months previously some of them were constantly at war, and their quarrels betrayed symptoms of great persistence; and if we remember how the observed behaviour of the birds suggests the fact that they were striving to attain some- thing definite, we shall understand the nature and extent of the change, and shall, I fancy, be in a better position to estimate its biological worth at its true value. We can find many similar examples—flocks are to be found on arable ground, on the water meadows, and on the mud-flats; here different kinds of Thrushes feed on the berries of the yew, there different kinds of Tits travel together in parties ; hosts of Finches collect in the hollies to pass the night and Buntings roost together in the gorse; and, in fact, in whatever direction we choose to look in the autumn and winter, we find various birds assembled together and living on amicable terms. All of this changes in the spring, and the relationship undergoes a gradual but noticeable alteration; so much so that whereas the outstanding feature of bird life in the winter is sociability, that of the spring 1s hostility. Q2 232 WARFARE BETWEEN DIFFERENT SPECIES So much, then, for the seasonal change of relationship ; let us now turn to particular cases and attempt to trace the condition which accompanies such change. Many migrants in the spring seem to follow the course of the Severn during their journey northwards through Worcestershire ; and where the river bends to the north-west at Lincombe Lock, there they leave it, or, rather, continue in a north-easterly direction which takes them across the southern end of Hartlebury Common. As I have already mentioned, this Common is overgrown with gorse, heather, and ling, and scattered here and there are a number of dwarf oak-trees and small elder-bushes. The situation is therefore an ideal one for the smaller migrants to rest for a brief time, and, from the point of view of the observer, very suitable because it is open and the movements of the birds can be traced for some distance. Turtle Doves pass over at a great height, or skim across a few feet above the gorse; Redstarts settle for a few minutes and then disappear; Tree-Pipits, Whinchats, and Willow-Warblers pass from tree to tree or flit from bush to bush—and all in a north-easterly direction. They do not sing, they are restless, and, judging by their behaviour, they are anxious to conceal their presence, not to make it known. Yet we know that when they reach their destination, as presently they will, all this will change; that each of them will employ every means at its disposal to make itself conspicuous ; and that CONDITION ACCOMPANYING CHANGE 233 each, as far as it is able, will resist intrusion on the part of other species. Now the southern end of the Common is always inhabited by individuals belonging to one of these species, or to others of close affinity ; so that wherever these travellers settle whilst passing across it, the chances are that they will find the ground oceupied—and their behaviour under such circumstances is no less interesting than the behaviour of the bird upon whose ground they are trespassing. We will take the case of the Whinchat. It arrives from the south-west, and, flying from bush to bush, works its way in a north-easterly direction. In doing so it intrudes upon the territory of a Stonechat; and the Stonechat, becoming excited, flies towards it, and it retires for a short distance in the direction from whence it came. Here again it is followed and attacked and again moves on, and then, flying in a circle as if to avoid the territory which blocked the path, resumes its former line of flight, though still followed by the Stonechat, which after continu- ing the pursuit for perhaps a quarter of a mile, suddenly turns in the air and returns to its headquarters. It is difficult to put oneself in the place of the Stonechat or of the Whinchat. But even after making due allowance for the danger inseparable from any attempt to do so, there remains the unquestionable fact that whereas the impulse to attack was strong in the one, the impulse to defend itself was wholly lacking in 234 WARFARE BETWEEN DIFFERENT SPECIES the other. Yet a Whinchat, when it has established itself, is most pugnacious; it not only attacks every bird of a similar size that approaches its position, but its behaviour under such circumstances bears the impress of unusual determination ; and if we were to take a male and place it in the position of the Stonechat, we should find that its nature would change, that the presence of the Stonechat would evoke a hostile response, and, conversely, that the instinct of the Stonechat would not be suscep- tible to stimulation. Hence it is clear that the nature of a bird when on migration is not quite the same as it is when its destination is reached ; that the positions occupied from time to time during the journey carry no meaning, or, rather, are not brought into relation with its life in quite the same way as is the position which it finally occupies ; and further, it is clear that the interest it displays in other species undergoes a somewhat remarkable transformation when at length its destination is reached. This altered nature of the migrant is a fact of some importance in relation to our present subject, but it does not stand alone—the same characteristic is observable in other phases of bird life. Some of the residents, the Buntings and the Finches for example, occupy their breeding ground very early in the year, and it often happens that the situations which they select are not capable of supplying them with food so early in the season, though at a later date food will be there in abundance; so that CONDITION ACCOMPANYING CHANGE 235 they are compelled to resort to the surrounding neighbourhood, and since, even there, the available supply is sometimes scarce or, if plentiful, limited to certain areas, they are constrained from time to time to join together again in flocks. Thus, for part of the year, they may be said to lead a double existence ; for just as the Whinchat, that is sociable on migration, betrays a changed nature when it reaches its destination, so too does the nature of these residents change from hour to hour according to whether they are seeking food or occupying the breeding ground. In the newly-sown fields of grain the birds frequently find a supply of food. Here Yellow Buntings, Greenfinches, and Chaffinches collect from the surrounding neighbourhood. The majority are somewhere in possession of terri- tories, and not a few are paired. Between the territories and the feeding ground a highway is formed by individuals passing to and _ fro. Sometimes both members of the pair leave together in order to seek food, at other times they separate and the male may be in his territory whilst the female is with the flock. Apart from occasional manifestations of sexual emotion on the part of a male, there is nothing to disturb the harmony of the flock nor any- thing in the behaviour of the birds which would lead one to suspect that, when they return, their nature will change and that they will be no longer sociable ; and, which is still more remark- able, no matter how great the provocation which 236 WARFARE BETWEEN DIFFERENT SPECIES an individual, when in company with the flock, may be called upon to endure, its customary hostile response will fail to be elicited. An incident which happened in the spring of 1917 will serve to make this clear. A flock of some thirty Yellow Buntings, Greenfinches, and Chaffinches were feeding in one corner of a field which had recently been sown with barley. As they sought their food they wandered outwards into the middle of the field, and in so doing, passed across the territory of a Sky- lark. Whereupon the Skylark became excited, uttered its call-note rapidly, and rising a few feet from the ground, attacked those members of the flock that were nearest, which happened to be the Yellow Buntings; and so determined were its onslaughts that the Yellow Buntings were forced to retire. The Skylark showed no discrimination as to sex, but attacked both males and females, and within a few minutes succeeded in driving away at least two pairs. One would have expected that the Yellow Buntings would have made some show of resistance; one would have thought that the fact of being violently attacked would have supplied a_ stimulus sufficiently strong to evoke a corresponding hostile response: yet there was no mistaking the lack of interest that they displayed in the contest—they made no effort to retaliate but seemed to accept the situation as unalterable and left. So far we have examined only those cases in which the pugnacious instinct was stimulated in CONDITION ACCOMPANYING CHANGE 237 one of the adversaries, and in which consequently the fighting seldom reached any high degree of severity. We must now consider some others in which each of the opponents acts as a stimulus to the pugnacious instinct of the other. It is here, of course, that we find the most violently contested battles, and it is here, too, that the purpose of the fighting seems clear. The persecution which the Green Woodpecker suffers from the Starling is well known. ‘The purpose of the Starling’s behaviour is clear, namely the possession of the hole occupied by the Woodpecker. Bird for bird, the Wood- pecker is more than the equal of the Starling, but persistent endeavour ultimately wins the day. The Starlings perch close beside the hole, and, whenever the Woodpecker shows itself, attack with determination; and not only do they do so but they are assisted, so there is reason to believe, by other individuals or pairs in the attainment of their end, so that no matter how stoutly the Woodpecker defends itself, in time it is almost certain to be deprived of its ownership. In like manner different kinds of Wood- peckers contend with one another for the possession of a hole, and here the opponents are more equally matched. [ have seen a pair of Lesser Spotted Woodpeckers endeavouring to drive away a Great Spotted Woodpecker. The excitement of all three birds was exceptional. Kach of the Lesser Spotted Woodpeckers kept swooping in turn at their rival, sometimes in the 238 WARFARE BETWEEN DIFFERENT SPECIES air and sometimes when it was settled on the topmost branches of a dead tree, and the sounds produced reminded one of the piping of a flock of Oyster-Catchers in flight. A battle between a pair of Green Wood- peckers and a Great Spotted Woodpecker is worth mentioning. It occurred on the 24th of April. Passing through the middle of a wood, I noticed a Great Spotted Woodpecker fly out of a hole in an oak-tree. Shortly afterwards, a pair of Green Woodpeckers settled near the hole and then flew to some oak-trees close at hand, where they were joined by their rival and signs of hostility were soon apparent. Presently the Great Spotted Woodpecker returned to the hole and entered. Both of the Green Wood- peckers then flew into the tree; and one of them, settling. upon the trunk, climbed up to the level of the hole and, when it became aware of the Great Spotted Woodpecker within, extended its wings fully and proceeded to peck viciously at its opponent. Whereupon there was a scuffle at the mouth of the hole and the Great Spotted Woodpecker hurriedly left. After this, all was quiet and the Green Wood- pecker eventually descended and entered the hole. The Great Spotted Woodpecker, how- ever, returned again, but, after fluttering around the hole, disappeared, leaving the Green Wood- peckers in possession. In this varied field of hostile behaviour which we have explored, one feature stands out prominently, namely, that the interest ‘ a : - i] > : - , - ‘ ‘ : ~ . * . ‘ ‘ q j ated ‘ ‘ ‘ - . < = ‘ t : - - _ See + a j - ” - e 2 2 waa, . nic i ERRATUM , For “pair of Pied Woodpeckers’ read ‘ Great Spotted Woodpecker ” To be inserted at p. 238. he - 4 ‘ me pea CONDITION ACCOMPANYING CHANGE 239 which a bird displays in other species varies not only at different seasons but even from hour to hour. I have used the word “nature” as equivalent to “interest,” and I:have spoken of the bird’s nature changing or altering accord- ing to the circumstances in which it was placed. But its nature is its inborn constitution, and its constitution cannot change from day to day, still less from hour to hour. So that, in a sense, and having regard to strict scientific accuracy, it is misleading in this particular connotation to say that the bird’s nature changes. What then does happen? The instinct of pugnacity must form just as much a part of the hereditary make-up of the migrant, when on migration, as when finally it reaches its destination ; still more must it form part of the constitution of the Bunting when it leaves its headquarters temporarily and joins the flock. And, if it is there, the question arises as to why it does not respond. Now every instinct requires for its response a stimulus of an appro- priate kind, and, therefore, a reasonable view to take would be that the necessary stimulus was lacking. But this is a view which we cannot uphold, because on all these occasions an opposing male was present—and, so far as it is possible to judge by observation, that is the stimulus which in the main evokes a hostile response. We must therefore look elsewhere than in its direction for a reason which will adequately explain the behaviour. Though it be true that every instinct 240 WARFARE BETWEEN DIFFERENT SPECIES requires for its functioning a stimulus of an appropriate kind, yet it is also true that the condition which will render it responsive must be present. What we have then to consider is whether the phenomena which we have explored give us any clue as to the particular nature of that condition. In the first place, we have the general fact that the hostility is not confined to a few species belonging to a few families, but that it is of wide application—birds of prey, Warblers, Woodpeckers, all supply us with evidence which serves to show, in greater or less degree, its nature and extent. Next, we found that the hostility was peculiar to a certain season—and that one the season of reproduction. And if the question were asked : What condition would then be most likely to render the instinct susceptible, the answer that would most certainly be given would be—the presence of a female. And in reply to a further question as to the particular nature of the stimulus to which the instinct would respond, we should be told—the presence of another male of the same species. Now the possible influence of the female on the course of the male’s behaviour was the subject of inquiry in the second chapter, wherein we endeavoured to explain the hostility between males of the same species, and we came to the conclusion that it was not alone sufficient to account for the facts disclosed. Still less likely, therefore, is it that her presence can bear any direct relation to the hostility CONDITION ACCOMPANYING CHANGE 241 between different species, the more so since the biological end of securing a mate is definitely excluded. And we have something in the nature of proof of the correctness of this view in the fact that she accompanies her mate when he joins the flock, and that there his instinct is not susceptible to stimulation. We then proceeded to examine certain cases in which all the indications pointed to the fact that the “will to fight” was present in only one of the opponents ; and we attached consider- able importance to this circumstance, because we knew from experience that the same bird which seemed to lack courage, could at other times and in other situations be most aggressive. If then we ask what condition was present on the one occasion that was absent on the other, we have no difficulty in finding a reply—on every occasion on which the opponents appeared to be unevenly matched, one was in occupation of a territory and the other was not. And if we inquire further as to which of the two was the aggressor, the answer is again clear, namely, the bird that occupied a territory. Finally we considered some particular instances in which the “will to fight” was present alike in both opponents, and in which the battles were protracted and severe. But the fact that a bird has established a territory is not in itself sufficient to render its hostile nature susceptible; it must be actually in occupation if a response is to be elicited. We reach this conclusion step by step: the 242 WARFARE BETWEEN DIFFERENT SPECIES behaviour of the migrant, that lacks the “ will to fight” when on migration but is pugnacious when it has secured a territory, shows it; the behaviour of the resident, which temporarily joins the flock and is there sociable, shows it ; and it is shown also by the determination with which both opponents fight when the question of ownership of a station is in dispute. And of all the facts we have reviewed, this is perhaps the most important in relation to our present subject, for it demonstrates that the change from sociability to hostility is not merely an . incident of the sexual season, not merely an indirect result of the functioning of the general disposition which leads to the establishment of a territory, but that it is intimately associated with the whole process, and that the particular part of the bird’s nature which is concerned is so nicely balanced that it will respond under one condition and one only. Thus we are led to the only conclusion which seems consistent with the facts, namely that there is a_ relationship between the “territory” and the hostility. If we are satisfied that all this warfare is not merely an expression of an instinct which is serviceable in another direction, what part does it play in the whole scheme of reproduction ? The young of many birds are delicate at birth and unable to withstand exposure to cold, and in the previous chapter we came to the con- clusion that the territory was serviceable in that BIOLOGICAL VALUE OF THE WARFARE 243 it provided an adequate supply of food in the vicinity of the nest, and thus obviated the necessity of the parents being absent from them for long. But manifestly no matter how active a male may be in driving away members of its own sex and kind, it will neither make its position secure, nor insure a supply of food for its young, so long as any number of individuals of different kinds are allowed to establish themselves in the same _ space of ground. On the one hand, then, we have the fact that there is constant strife between males of close affinity, whilst on the other, we know that many species require like conditions of existence and are bound to assemble wherever these conditions are suitable; and we can infer that the territory would fail to serve its purpose if no restriction were imposed upon the measure of such assemblies. The question then arises: Does all this warfare contribute towards the attainment of reproduction? Not far from my house there is a small water meadow, three acres in extent, which for some years has been derelict and is now overgrown with the common rush (Jwncus communis) and small alder trees. For three successive seasons I watched the bird life of this meadow, and more especially the Reed-Buntings whose behaviour I was studying at the time. In every respect the meadow was suitable for this bird; there was an abundance of food and numberless situations in which nests could be placed. Each year all the pairs were successful R 244 WARFARE BETWEEN DIFFERENT SPECIES in rearing one, if not two broods, yet the number of pairs never exceeded five—the first year there were three; the second year five; and the third year four. In addition to the four pairs of Reed-Buntings, there were in the spring of 1915, six pairs of Whitethroats, one pair of Lesser Whitethroats, four pairs of Willow-Warblers, one pair of Sedge-Warblers, two pairs of Grasshopper-Warblers, one pair of Chiffchaffs, three pairs of Hedge-Sparrows, two pairs of Tree-Pipits, one pair of Skylarks, one pair of Whinchats, one pair of Flycatchers, two pairs of Song-Thrushes, one pair of Blackbirds, one pair of Redstarts, three pairs of Chaffinches, and one pair of Wrens—in all, thirty-five pairs, whose young were mainly dependent for their living upon the insect life of that meadow and the ground immediately surrounding it. If we allow three young to each pair—and this would take no account of second broods—we arrive at the following result, namely, that one hundred and five young and seventy adults had to be supplied with food from that locality, which would mean, if the search for food were strictly limited to that meadow, that 83 square yards would be allotted to each individual. Suppose now that the four male Reed- Buntings had each admitted one other male, and that they had secured mates, what would have been the effect upon the whole community ? The four additional pairs with their young would have represented twenty individuals, which would have represented a decrease of BIOLOGICAL VALUE OF THE WARFARE 245 8°5 square yards in the space allotted to each individual. The pressure of the bird population upon the means of support would then have been materially increased; and not only the Buntings, but the Warblers, Pipits, and all the rest would have suffered. But the result would have been the same if, instead of the four additional male Reed-Buntings, four males of other kinds had been allowed to enter the marsh, and we can multiply the number four until we arrive at a point when the means of subsistence would no longer have been adequate for the adults, still less for the young. If, then, there were nothing to pre- vent this happening, many of the birds in that marsh would have no chance of rearing their young successfully. Hence, if the territory is adequately to serve the purpose for which we believe it has been evolved, some provision must have been included in the system to meet the difficulty. There are three ways by which this may have been accomplished—indirectly, by increasing the size of the area occupied by each individual, and thereby reducing the relative number of each species; or directly, by rendering the fighting instinct of the bird susceptible to stimulation by individuals of other species ; or, possibly, by a combination of the two. ‘There were four pairs of Reed-Buntings in the marsh, and their territories covered the whole of it. But inasmuch as other insectivorous birds were established there also, and found sufficient food 246 WARFARE BETWEEN DIFFERENT SPECIES to maintain both themselves and their families, it is clear that the area these Reed-Buntings occupied was in excess of that which they would have required if they had been the sole inhabitants. And such often appears to be the case. Many a Warbler allocates to itself a space of ground more than sufficient to supply it with all that it needs; so, too, does the Finch, or the Pipit, or the Falecon—if we take no account of kindred species. Thus there is reason to believe that, by limiting the number of individuals in a given locality, this apparently wasteful expanse of territory is serviceable in that it provides against the pressure of the bird population upon the available means of support becoming too great. But though a reduction in the numerical standing of the different species would certainly follow from any increase in the area occupied by the respective individuals, and with even greater certainty would place them in a more secure position as regards their supply of food, yet, when we remember how large a number are dependent upon a supply of insect life for their young, we can. understand that it would not alone be a sufficient safeguard against the dangers attendant upon _ over- crowding. It is here, I believe, that we shall find the true explanation of the hostility ; it roughly insures that the number of pairs in any given area does not exceed the available means of support, and indeed it is difficult to imagine how such uniformity of distribution as would free the young from the risk of BIOLOGICAL VALUE OF THE WARFARE 247 exposure could be obtained without some such control. Some birds, however, have no difficulty in finding the necessary food for their young, yet have great difficulty in finding a station where they can rear their young in safety; and the area each one occupies has been reduced to the smallest proportions in order that the maximum number can be accommodated. Here, any increase in the size of the territory would inevitably lead to the extinction of the race, so that nothing stands between failure and success except the ability of the bird to defend its territory. If we study the bird population at one of the breeding stations on the coast, we find, generally speaking, that each kind of bird inhabits a particular portion of the cliff; on the lower ledges are the Guillemots and Kitti- wake Gulls; higher up are Razorbills and Fulmars, and at the top, where the cliff is broken and the face of the rock covered with turf and soil, the Puffin finds shelter for its egg. At the same time there is much over- lapping ; the kind of ledge that suits a Razor- bill is equally suitable for a Guillemot or a Fulmar, and so, no matter how successful the Razorbill may be in establishing a territory and preventing intrusion upon it by other Razorbills, it will be all to no purpose if it allows itself to be jostled out of its position by a Fulmar. Hence, inasmuch as breeding stations are limited and competition for territory so severe, only those forms in which the fighting R2 248 WARFARE BETWEEN DIFFERENT SPECIES instinct responds freely to a wide range of stimuli will be in a position to maintain a footing upon the cliff. In trying to estimate the importance of the hostility in its relation to the territory, we must, bear in mind that competition varies in different seasons and in different localities. The surface of the land is constantly undergoing modification, partly owing to human and partly to physical agency—forests are cleared; marshes are drained; the face of the sea-cliffs is altered by the erosion of the waves; here the coast may be locally elevated, there locally depressed; and so forth. Many of these changes are slow and imper- ceptible, many can be observed in our own lifetime. The timber is felled and the under- growth cleared in some wood, and the following spring we notice a change in the character of the bird population. Migrants which formerly found in it no suitable accommodation now begin to appear, and as the seasons pass by and the undergrowth affords more and more shelter for the nests and an increasing supply of insect life, so their numbers increase until the wood becomes an important breeding station, resonant with the song of many individuals. But slowly the growth increases; the bushes pass into saplings and the saplings into trees, and the undergrowth then disappears just as surely as do the migrants which can no longer find there the conditions which they require. Or, as an illustration of the effect produced BIOLOGICAL VALUE OF THE WARFARE 249 by natural agency, let me describe a change which has taken place in a corner of Co. Donegal. The promontory of Horn Head is bounded on the west by extensive sand-hills, 100 ft. or more in height. On the southern side it is divided from the mainland by a channel, which narrows down to 100 yards or so in width where it fringes the sand-hills, and then widens out again, covering an area of approximately 270 acres. As far as is known in the memory of man, this area has always been tidal. But in recent years a change has taken place, and the blown sand has silted up the channel, with the result that this tidal area has been transformed into a brackish lake. What has brought about the change is not easy to determine. There is evidence, however, of a slow alteration of the level of the shore-line; for in the midst of the sand-hills, situated 150 yards or so from the present sea-margin, and running parallel with it, there is an accumulation of pebbles some 3 feet high by 4 feet deep. This raised beach is now separated from the Atlantic by sand-drifts of considerable height, and consequently there are some grounds for believing that secular elevation is taking place, which, if it be the case, will account for the change in progress. Now the effect on the bird population can be seen even now, and will doubtless become more apparent as the years pass by. Sand-Martins used to find plenty of places to breed amongst the sand- drifts, and moreover do so still. But their nesting sites are constantly changing and dis- 250 WARFARE BETWEEN DIFFERENT SPECIES appearing, and the breeding-place of one colony, that was situated in the bank of a stream twelve years ago, is now buried 10 feet or more below the surface of the sand. The area that was once tidal, but is now a brackish lake, is fed by mountain streams, and as the fresh water predominates, so in course of time will it become fringed with vegetation; and instead of the flocks of Curlew, Dunlin, and other waders that, at low water, resorted there to feed, Coots will fight with one another for the possession of territories, and the Wild Duck will teach her young to seek their food. In whatever direction we turn, we find that many breeding grounds are subject to incessant change. Ancient haunts disappear, new ones come into being, a change which makes life impossible for this bird, as likely as not benefits that one, and so on. There is no stability. Hence in any given district each recurring season there must needs be a large number of individuals which are obliged to seek new stations, and if there were no control over their distribution, if each one were free to establish itself wherever it chanced to alight, this locality might be overcrowded and that one deserted; and, bearing in mind how many species there are that require similar conditions of existence, we can infer that the successful attainment of reproduction would become impossible for many of those individuals so long as each species was indifferent to the presence of the others. On the other hand, if BIOLOGICAL VALUE OF THE WARFARE 251 there were no control over the range of the intolerance, the smaller bird would have no chance in competition with the larger, and it is doubtful whether the larger would gain an advantage commensurate with the energy it would expend in ridding its area of the smaller. I have described battles in which the opponents were only distantly related; for instance, the Moor-Hen will attack almost any bird—Part- ridge, Lapwing, or Starling—that approaches its territory even temporarily. Nevertheless the antagonism between kindred forms is more prevalent, and, as a rule, characterised by more persistent effort; and thus it seems as if the susceptibility of the fighting instinct has its limitations, the degree of the responsiveness being dependent upon the affinity of the opponents. Suppose now that we take an area inhabited by a number of different species requiring like conditions of existence, divide it into three sections, and imagine that in one they were all sociable, that in another they were all hostile, and that in a third those which were closely related were intolerant of one another. Let us suppose further that each one of them was represented by the full number of individuals that the law of territory would allow. In the first section an individual would establish itself, and, becoming intolerant of its own kind, would exercise dominion over an area roughly sufficient, providing conditions were normal, to insure an adequate supply of food for 252 WARFARE BETWEEN DIFFERENT SPECIES its young. But it would take no account of other species, and since any number might occupy the same ground, the fact of its having established a territory would not alone suffice to render its supply of food secure. Success in the attainment of reproduction would then become largely a matter of chance, depending upon the number of individuals that happened to settle in this place or in that. In the second section there would be perpetual warfare; for whereas the appropriate organic condition which leads to pairing arises in different species at different times, fresh claimants to occupied ground would constantly be appearing, and the efforts of the inhabitants to preserve their boundaries intact would have to be maintained throughout the whole period of reproduction; and while the stronger or more persistent forms would be more likely to breed, they would do so at the expense of their young, to which they would be unable to devote proper attention, and with an expenditure of energy that would reflect itself upon the future of the race. But the conditions of life in the third section would be such as would be more likely to yield good results. The relations of the different members of the community would be more evenly balanced, for a male would only be called upon to compete with those of its own size and strength. Thus, on the one hand, accommodation would be so divided as to secure the breeding of the maxi- mum number of individuals with the minimum of expenditure of energy, whilst on the other, SUMMARY 253 any undue pressure upon the available means of subsistence would be prevented. There can be no question that in the latter section a higher percentage of individuals would succeed in rearing offspring. And so, by reason of the fighting instinct being more susceptible or less susceptible according to the affinity of the opponents, a control is established which, while preventing unnecessary extension of war- fare, allows for sufficient extension to render the biological end secure. These, then, are the facts—this the conclusion which can be drawn from them. It may, however, be said of thesé facts, as it has been said, with even less justification, of the battles between individuals of the same species, that they do not afford evidence of genuine hostility. No doubt there are many naturalists who could supplement these facts with others in which the conflicts resulted in bodily injury, or terminated fatally, or at least were of a more determined kind. But I have already drawn attention to the fact that, so long as a definite result is attained, the severity of the struggle and the amount of injury inflicted are matters of small moment. Let us, however, run over the sub- stance of the argument, and then briefly refer again to this point of view. After enumerating instances of hostility, sufficient in number, so it seemed, to constitute reasonable ground for the belief that they had a part to play in the life-history of the 254 WARFARE BETWEEN DIFFERENT SPECIES individual, the two questions we set ourselves to examine in this chapter were: Is there any circumstance in the life behaviour of the individual with which the hostility can be definitely related; and, will the hostility lead to the securing of a greater measure of success in the attainment of reproduction? Many different species assemble together in winter and roam from place to place in search of food. But in spring their behaviour undergoes a remarkable transformation; they avoid one another and become quarrelsome, so much so that whereas the outstanding feature of the winter is sociability, that of the spring is hostility. With this general fact before us, we proceeded to investigate this change of behaviour still further. First of all we took the case of a migrant, and, comparing its behaviour, as it journeyed, with that when finally it reached its destination, we found that the bird which was notoriously pugnacious when in occupation of a territory betrayed no interest in other species as it travelled to the accustomed breeding ground. Not only so, but even though it was attacked, we found that its pugnacious instinct still failed to respond. Here, however, it may be contended, and with reasonable justification, that in the interval which elapses before the ultimate destination is reached, some change in the organic con- dition of the bird may occur which will account for its altered behaviour; or, it may be urged, with no less justification, that whereas on SUMMARY 255 migration the bird is unpaired, when the destination is reached it is probably in posses- sion of a mate and is therefore quarrelsome. Now, at the most, the interval can only be a matter of a few days, and it is unlikely that organic changes sufficient to bring about so important an alteration of behaviour could occur in so short a time, still less likely that they could be timed to come into functional activity just at the moment when the bird reaches its breeding ground. And with regard to the suggestion that the change can be accounted for by the presence of a mate, we shall do well to remember not only that males as a rule precede the females by some days, but that a male may even remain in its territory, mateless, for some weeks, and yet display hostility. Nevertheless the case of the migrant did not, by itself, afford sufficient evidence upon which to base any conclusion. We therefore inquired into the behaviour of some of the residents at a corresponding period. ‘The Bunting served as an illustration. Early in the season it estab- lishes a territory, and because food is then scarce it is forced to seek it elsewhere than on the small plot of ground which it has acquired ; and so it makes its way to some spot where the supply is abundant, and there, meeting with other species bent on a similar errand, forms with them a flock. Part of its time is then spent in the territory and part on the feeding ground, and between these two points a 256 WARFARE BETWEEN DIFFERENT SPECIES highway is formed by the bird passing constantly to and fro. But the attention which it pays to other species is very different on these two occasions—when in the territory it is intolerant of strangers, but when it accompanies the flock it displays no interest in their movements. From hour to hour its nature seems to change. But, as we saw, the inborn constitution of the bird cannot change, and therefore we came to the conclusion that an explanation of the altered behaviour was to be found in the fact that the pugnacious instinct is only rendered susceptible under a certain condition. So that all the evidence tended to confirm the impression which we had gained from the course of events in the life of the migrant, namely, that the hostility bears a direct relation to the occupation of a territory. Finally we were led to inquire whether the hostility was serviceable in promoting the welfare of the individuals. We saw that many different species require similar conditions of existence, that ancient breeding haunts dis- appear and that new ones come into being, and that in the ordinary course of events such species must often assemble in the same area for the purpose of reproduction. So that even though a male might be successful in protecting its ground from intruders of its own kind, yet it might still fail to rear offspring, just because it happened to choose a position in which other kindred forms had gathered. Hence if the territory is adequately to serve its purpose, SUMMARY 257 some control over the local distribution of species is of paramount importance. Neverthe- less, if all the different forms that require similar conditions of existence were intolerant of one another in a like degree, the smaller bird would have no chance in competition with the larger. This, however, is not the case. Some, as we saw, arouse little or no animosity in others, in fact the more closely related the rivals, the more responsive their pugnacious nature seems to become. To return now to the view that the fighting is not really serious, but, on the contrary, that it is either vestigial and has no longer any part to play in furthering the life of the individual, or that it is a by-product of the seasonal sexual condition to which no meaning can be attached. First, there is the relationship with the territory, and this, it seems to me, is a fact of some importance ; for if the fighting were merely an exuberant manifestation of sexual emotion, one would expect to find it occurring under all conditions, and not merely under one particular condition in the life of the bird. The hostility is too widespread, however, and too uniform in occurrence for us to suppose that it has no root in the inherited constitution of the bird; and if it served some useful purpose in the past, the instinct might still persist, so long as it were not harmful. Thus the view that the behaviour is vestigial is not perhaps unreasonable. But manifestly it makes no difference whether it be vestigial or a by-product of sexual emotion, 258 WARFARE BETWEEN DIFFERENT SPECIES whether the battle be fierce or so trivial as to appear to us to be more in the nature of “play,” so long as some change in the relative prospects of the opponents is the result. For us, then, the main consideration lies in the question: Is the behaviour serviceable now in furthering the life of the individual ? Whether the evidence which we have examined affords sufficient ground for the belief that the hostility is genuine and has a part to play in the whole scheme of reproduction, each must judge for himself. CHAPTER VII THE RELATION OF THE TERRITORY TO MIGRATION CoINCIDENT in time with the growth of appropriate conditions in the environment, organic changes take place rendering certain instincts susceptible to stimulation; and the stimulus being applied, the Warbler leaves the country wherein it had passed the winter and finds its way back, with apparently little difficulty, to the district in which it was reared or had previously reared offspring. What is the nature of these changes and of the impulse which is first brought into functional activity ; whence comes the stimulus; and what directs the bird on its journey—these are all different aspects of one great problem, the problem of migration. I do not propose to discuss all these various aspects, for indeed I have no suggestions to offer which are in the least likely to be helpful, but I seek rather to ascertain whether the phenomena which we have explored bear any relation to the problem as a _ whole; whether, that is to say, the competition for territory and all that appertains to it can have 259 Ss 260 RELATION OF TERRITORY TO MIGRATION supplied the conditions under which, in the process of time, this complex and definite mode of behaviour has evolved. We are sometimes told that we must seek the origin of migration in the physical changes that have occurred in the ancient history of the earth—in glacial conditions which gradually forced birds to the south, or in the “stability of the water and mobility of the land” which brought about a gradual separation of the feed- ing area from the breeding area—and which continued for a sufficient length of time to lead to the formation of an instinct, and that the instinct persists because it is serviceable in promoting the welfare of the race. But when we consider the lapse of time, and the changes that must have occurred in the character of the bird population—the appearance of new forms and the disappearance of the old, the ebb and flow of a given species in a given area—and bear in mind that, notwithstanding this, the migratory instinct, if not stronger, is assuredly no less strong, and the volume of migration, if not greater, is assuredly no less; in short, that the whole phenomenon is progressive rather than retrogressive, we shall find the view that the instinct owes its origin to conditions which no longer exist, receives but little encourage- ment. I doubt not that, throughout the ages, geological changes have been an important factor in directing or limiting the scope of migration, and moreover are so still; just as ROUTINE UNIFORM 261 climatic changes and the relative abundance or scarcity of enemies have influenced the course of-its evolution. These are all contributory factors operating in the external environment. But there are, besides, internal factors which _ form part of the inherited constitution of the bird, and, being passed on from generation to generation, afford the conditions under which migration is constantly being renewed. It is, I believe, in this field of organic change and relationship that the conditions of origin must be sought. Just as the moth in passing from the rudi- mentary to the perfect condition runs through a series of changes, each one of which is marked by a typical behaviour response adjusted to meet some particular circumstance in the external environment, so the annual history of a bird displays an ordered routine, each phase of which can be observed to correspond with one of the successive changes in the environment. In almost every direction, we find that this routine is characterised, in broad outline, by great uniformity ; so much so that, providing we know the history of one species, we can forecast with no small degree of certainty the general course of behaviour of other members of the family.. But only the general course. There is endless variation in just the particular way in which the behaviour is adapted to meet the needs of particular species—the major details may be said to be specific, the minor details varietal. 262 RELATION OF TERRITORY TO MIGRATION Now it is that part of the behaviour routine which has reference to the relationship between one bird and another upon which, for the time being, I wish to dwell; for the interest that A displays in B is by no means always the same—it changes according to the season, and this change can be observed to be uniform throughout a wide range of species. In winter, in whatsoever direction we turn, we observe not only that different individuals but that different species also collect together in flocks. And since food at that season is not always easy to obtain, and, moreover, is only to be found in certain situations, which are limited both in number and extent, it would seem that such assemblages are in the main determined by accident. No doubt the abundance or the scarcity of food does determine the movements of birds, and hence to that extent may be held to account for the flocks. But we shall but deceive ourselves if we think that it is the sole or even the principal reason, or that the situation is in no wise affected by internal factors. The behaviour of the individual in relation to the flock bears ample testimony to the presence of a gregarious impulse which derives satisfaction from the fact of close association. As an illustration, let us take a bird whose movements are easily watched, and in whose hereditary constitution the impulse to which I allude seems to be strongly implanted — the Curlew. When the breeding season is over, Curlew leave the mountain and the moor and GREGARIOUS IMPULSE 263 return to the coast or tidal estuaries for the remainder of the year. Here, at low water, they find an abundant supply of food—crustaceans amongst the sea-weed upon the rocks, and lob- worms (Arenicola piscatorum) in the mud as the tide advances or recedes. But when the tide is full, they retire to those parts of the shore that remain uncovered—to isolated rocks, or to sand- dunes, or it may even be to pasture-land in the neighbourhood. During this period of repose large numbers of individuals gather together on a comparatively small space of ground. ‘They are not constrained to do so by any shortage of accommodation, nor by any question relative to food, nor, for the matter of that, by any circum- stance in the external environment; they are brought together solely, this at least is the impression that one gains, by some inherited impulse working towards that end. And their subsequent course of behaviour tends to confirm that impression. For if we watch the gathering together of the different units of which the flock is composed, and study more particularly the emotional manifestation which accompanies their arrival and departure, we shall find that the coming of a companion arouses some emotion which is expressed by a vocal outburst that sweeps through the flock. Now each call, and the Curlew has a great variety, is not only peculiar, generally speaking, to certain occasions, but is accompanied by a specific type of behaviour, whence we can infer in broad outline the type of emotion which is S2 264 RELATION OF TERRITORY TO MIGRATION aroused. Thus we come to recognise fear, anger, or sexual emotion, by just the particular sound which is emitted. But even if we are going too far in referring particular calls to particular emotions, we can, without a doubt, divide them into two broad categories — those which are pleasurable and those which are the reverse. And we need have no hesitation in placing the particular call to which I allude in the first of these two categories, not only on account of the nature of the sound produced, but because the activities which are aroused are not such as normally accompany irritation. This is well seen if the behaviour of different individuals be closely observed. After resting on one leg for some time, first one and then another is seized with cramp, and running a few yards in an ungainly way, bumps up against its com- panions as if it had not full control over its movements. Its behaviour produces irritation which is expressed by a vocal outburst, and followed by actions the meaning of which is clear. Moreover, the call is taken up by other individuals and sweeps over part of the flock as does the greeting. But the nature of the cry is entirely different from that which greets the arrival of a companion—humanly speaking it is a passionate and impatient utter- ance, the height of displeasure. The arrival, then, acts as a stimulus to something in the inherited constitution which is expressed in, and presumably is satisfied by, this vocal outburst ; and, since the bird that arrives joins also in the GREGARIOUS IMPULSE 265 chorus, there is reason to think that the impulse which determines its movements is similar to that which is temporarily aroused in the flock. Apart, however, from the evidence derived from the affective aspect of the operation of the instinct, the general course of behaviour lends support to the view that the assemblies are determined by internal factors, and are not merely the outcome of circumstances in the external environment. Observe, for example, the manner in which the flock is built up. Single individuals are content to rest alone so long as no assembly is in sight, but they are drawn towards their companions directly the opportunity arises, just as surely as the smaller aggregation is drawn towards the flock ; and so, as the flock increases, it gradually absorbs all the lesser flocks and smaller parties, for the greater the flock the greater the attraction seems to be; and different individuals appear to gain some satisfaction from being in close bodily contact with one another. When the Curlew flies to that part of the mud-flat which is first exposed by the receding tide, and there associates with others, it does not then do so because it has any interest in its fellows, nor because they serve as an attraction, but because it is constrained by hunger—in other words, the association is determined by accident. But when, during periods of repose, it sees a flock, flies to it, and takes up a position in the midst of it, it does so not because suitable accommodation is lacking—not therefore because 266 RELATION OF TERRITORY TO MIGRATION of external constraint—but because it derives some pleasure from satisfying something in its organic complex. We speak of this behaviour and of the emotion which characterises it as the gregarious instinct: by which we mean that the inherited nature of the Curlew, as a tribe, is so constituted that, given the appropriate internal conditions and adequate external stimulation, every individual will respond in a similar manner —that is, the behaviour is primarily determined by racial preparation. This is what we mean by the gregarious instinct biologically considered. We may resolve our own experience in relation to the crowd into its simplest constituents, project our own primitive feelings into the Curlew, and say that the bird feels uneasiness in isolation and satisfaction in being one of the flock. But in truth we know nothing, save by analogy, of the correlated psychical state. All the knowledge we possess is derived from a study of the objective aspect of the behaviour, which in simple terms may be expressed thus: the individual is drawn towards its companions ; there is a relation between the size of the flock and the strength of the attraction; and all Curlew behave similarly under similar circum- stances. This instinct controls the movements of many birds from early autumn to the com- mencement of the breeding season. And so powerful is the control that the individual is suppressed and its activities subordinated to the welfare of the community as a whole. Flocks GREGARIOUS IMPULSE 267 of Waders roam about the tidal estuaries in search of food, and different kinds of Gulls assemble there and preen their feathers or sleep ; Warblers alter their mode of life, and in the osier bed, or amongst the elders, seek their food together in peace; Finches, Buntings, Pipits, and Wagtails, though food is everywhere abundant, gather themselves together respec- tively into bands which, as winter approaches, grow into flocks and even into composite flocks ; and as the Warblers leave for the south, so their places are filled by flocks of 'Thrushes and Finches from the north. In whatever direction we turn, when the days begin to shorten, it is the community, not the individual, that thrusts itself upon our attention; and throughout the winter continues to be the outstanding feature of bird life. With the approach of the breeding season we witness that remarkable change which I have endeavoured to make clear in the previous chapters—the disintegration of the flock and the reinstatement of the individual. Instead of continuing with the flock, the individual now goes forth to seek the appropriate breeding ground; and having arrived there, is not only content to remain in isolation, but so behaves that isolation is insured. Intolerant of the approach of a stranger, intolerant even of the approach of the very members of the community whose companionship was previously welcomed, it not only fights to maintain the position it has selected, but fights indeed for the possession of 268 RELATION OF TERRITORY TO MIGRATION ground already occupied, and, until reproduction is completed, asserts its individuality and exer- cises dominion over its territory. What, then, is the prospective value, biologically considered, of the changing interest that A displays in B, and to what will such changes lead? ‘These are the questions to which we will now direct inquiry. The annual life-history of a bird is in broad outline conditioned by two powerful and at first sight opposing impulses—the one to live in society, the other to live solitary. But, mani- festly, a bird cannot be governed by opposing impulses. It has but one character, within which, according to the season and the cireum- stances, different impulses predominate. But these impulses, no matter how different they may appear to be, have their respective parts to play in furthering the life of the individual. Hence they cannot oppose, though they may conflict, if the resultant behaviour contributes towards survival. The majority of birds live to-day in constant danger from predatory species, and that this danger was still greater in bygone ages there ean be but little doubt. A curious mode of behaviour of the Curlew, Whimbrel, and Godwit demonstrates this, for it must be the outcome of the necessity for constant watchfulness. Whilst resting with its head turned back and its beak buried in the feathers of the mantle, the bird constantly moves the axis of its body, so that an observer, if placed in a direct line GREGARIOUS IMPULSE SERVICEABLE 269 behind it, sees at one moment the right eye and at another the left. No movement of the feet or of the legs is perceptible, and the shifting of the body continues whether the eyes are open or closed. ‘This body movement enables the bird to survey a much larger area of ground than it would otherwise be capable of doing, and thus adds to its security. As far as my experience goes, the movement is less evident amongst the members of a flock than when an individual is resting alone, or even with a few companions, which may be due to the fact that since some members are always awake and watchful, a bird of prey would have more difficulty in approaching a flock unawares than it would have in approaching a single individual. With the greatest ease a Sparrow-Hawk can pick up a Thrush as it feeds on the meadow by itself, but if it attempts to seize one of a flock, the chances are that its approach is signalled and that its prey escapes. And not only do the different members give warning one to another of the approach of danger, but they also combine to harass or even to drive away an enemy. So that there can be no doubt that the gregarious instinct is service- able in promoting the welfare of the race, and has, as its end, the preservation of the individual in order that it may take its share at the appropriate time in procreating its kind. In winter, then, the individual loses its individuality and is subordinated to the welfare of the community, whilst in spring it regains 270 RELATION OF TERRITORY TO MIGRATION its individuality, and all its inherited instincts which then come into operation lead to its isolation from the flock. The impulse to seek isolation is dependent upon internal organic conditions which are peculiar to a_ certain season ; whereas the gregarious impulse depends upon internal organic conditions which inhere at all times, though its functioning is inhibited by the functioning of the former impulse. The evidence which leads to this conclusion is to be found in the fact that a male often deserts its territory temporarily and joins the flock, where it remains at peace with its companions— an aspect of behaviour which we have discussed on various occasions. ‘The former impulse be- comes dominant in the spring owing to its innately superior strength; the latter becomes dominant in the autumn because the organic condition which determines the functioning of the former then subsides. The impulse to seek the appropriate breeding ground and to dwell there would seem to be the strongest of all the impulses save one—the sexual. When, however, I speak of the sexual, I refer to the actual discharge of the sexual function, which is the consummation of the whole process. But the territory and all that appertains to it is part of that process — the search for the breeding ground, the dwelling there, and the intolerance of intrusion are but different stages, each one of which must have an impulse peculiar to it; and since the completion of the sexual act can only be EFFECT OF ISOLATION 271 successfully accomplished providing that success is attained at every stage, the probability is that, of the impulses concerned, one is neither more powerful nor less powerful than another. So that we have two impulses operating at different seasons and guiding the behaviour into widely divergent channels. But though the proximate end to which the behaviour is directed is apparently different, there are not two biological ends in view, but one— the attainment of reproduction; and the changes that we witness are not contrary but comple- mentary, and their prospective value lies in the circumstance that they contribute towards the preservation of the race. If, then, every male is driven by inherited impulse to seek the appropriate breeding ground each recurring season ; if, having arrived there, it is driven to seek a position of its own; if, in order to secure isolation it is obliged to attack other males or to ward off the attacks of intruders; if, in short, success can only be attained providing that the inherited nature is so adjusted that the bird can accomplish all that is here demanded—what will be the general result? That the individual will rear its off- spring in safety and that they will inherit the peculiarities of their parents, enabling them, in their turn, to procreate their kind; all this will certainly follow. We are not concerned, however, at the moment, with the direct effect upon the individual, but with the consequences that will accrue to the species as a whole. 272 RELATION OF TERRITORY TO MIGRATION Now certain facts are presented to observa- tion which enable us not only to understand the nature of the change that is wrought in the history of the species, but to foreshadow, with no small degree of certainty, the extent of that change. I suppose that it has come within the experience of most of us to observe, at one time or another, the ebb and flow of a given species in a given district. Some favourite haunt is deserted for a year, or for a term of years, and is then revisited; or, if it is always occupied, the number of inhabitants fluctuates—plenty of pairs in this season, only a few in that. Many intricate relationships, both external and internal, contribute towards this state of affairs. Fluctuation in a downward direction, or temporary extinction, is brought about by changes in the physical world, by changes in the available supply of food, by the increase of enemies, or by adverse climatic conditions ; whilst fluctuation in an upward direction, though due indirectly to a combination of circumstances in the external world favourable to the survival of large numbers of individuals, is directly determined by the impulse to seek isolation. As individuals of different species establish themselves, and form kingdoms and _ lesser kingdoms, we can watch the gradual quickening into life of moorland and forest and we can observe the manner in which it all comes to pass. Males that for weeks or months have lived in society, drifting from locality to locality according to the abundance of food or its EFFECT OF ISOLATION 273 searcity, now set forth alone and settle first here and then there in search of isolation. Lapwings settle in the water meadows, and, finding them- selves forestalled, pass on in search of other ground ; Blackbirds arrive in a coppice or in a hedgerow and, meeting with opposition, dis- appear; and the Curlew, wandering with no fixed abode but apparently with a fixity of purpose, searches out the moorland where it can find the particular environmental conditions to which its inherited nature will respond. In fact, wherever we choose to look, we can observe in a general way the gradual appropria- tion of breeding ground; and if we fix our attention upon particular males, we can watch the method by which success or failure is achieved. On more than one occasion I have watched the efforts of Reed-Buntings to appropriate territories in a marsh that was already inhabited. Sometimes their efforts met with success, at other times with failure. In the former case, the males, whose ground was intruded upon, were severally forced to yield part of their holding and were thus left in possession of a smaller area. ‘The success of the intruder seemed to depend upon persistent determination, rather than upon superior skill in battle. Recently I had an opportunity of observing the intrusion of a male Willow-Warbler upon ground already occupied. By persistent effort it succeeded in appropriating one half of the territory of its rival. The intruder occupied some trees on the 274 RELATION OF TERRITORY TO MIGRATION outskirts of the territory it was invading, and used them as a base from which it made repeated efforts to enter the ground of its rival. These efforts were time after time frustrated. No sooner did it leave its base than it was seen and intercepted, or else attacked ; and no matter from which direction it attempted to effect an entrance, its efforts, for a time, were all to no purpose. The fighting was of a determined character, and after each attack the owner of the territory showed signs of great excitement, and, sitting upright upon a branch, spread and waved its wings, which is the specific emotional manifestation during the period of sexual activity. Eventually the intruding male suc- ceeded by persistent effort in appropriating part of the occupied ground. Thus we can actually witness the efforts of the individual to isolate itself from members of its own kind, and can observe the immediate consequences that follow from success or from failure. And from these consequences we can infer that, within a certain range but in accord- ance with the relative abundance of the species that dwell in it, every corner of the available breeding ground will be explored and every situation that evokes the appropriate response will be occupied. Moreover, since the annual dispersion is not merely a repetition in this season of that which occurred in a previous one, a progressive increase in the area occupied will follow. Yet, if the majority of species desert their breeding ground so soon as reproduction is EFFECT OF ISOLATION 275 ended, how can this be? An answer to the question will be found in the fact that a bird has an innate capacity to return to the neigh- bourhood of its birthplace, or to the place wherein it had previously reared offspring— which means that the results of prior process persist as the basis and _ starting - point of subsequent process. Bearing then in mind that the seeming peace in bird life around us in the spring is but the expression of transitory adjustments in the distribution of individuals and of species ; bearing in mind how widespread is the search for isolation each recurring season, how frequently the search leads to competition and competition to failure, and how failure implies a renewal of the search; bearing in mind that situations, which appear to be eminently suitable for breeding purposes, are passed by year after year and remain unoccupied, just because, for reasons which have yet to be ascertained, the environ- ment fails to supply some condition which is essential if the inherited nature of the bird is to respond—can there be any doubt that the general result of the functioning of the disposi- tion will be expansion; or, since no limit is placed upon it from within but only from without—that is, by unfavourable circumstances in the external world, that the expansion will not merely be in one direction but in every direction @ If now, when reproduction is ended, all the impulses relating to it die away, and the 7 276 RELATION OF TERRITORY TO MIGRATION gregarious instinct again predominates, what are the consequences to which this change will lead? Just as the consequences which flow from the functioning of the former impulse are accessible to observation, so likewise can we observe the change that is wrought by the latter impulse. The process is a gradual one. Less and less attention is paid by the individual to intruders, more and more is it disposed to pass beyond its accustomed limits. Little by little, accompanied by its young or without them, as the case may be, the bird deserts its territory and wanders out into the wilderness. Here it associates with others, and finds in them a new interest and, I doubt not, a new enjoyment. All this we can observe as it takes place. But just as there is an innate capacity to seek, in the spring, the place where the pleasures of breeding had formerly been enjoyed, so we are bound to infer the existence in the adult of an innate capacity to revisit the former area of association ; and this capacity,will strengthen and confirm the gregarious instinct and set the direction of the general course of movement. We have seen, then, that the interest dis- played by one bird in another changes with the seasons ; we have seen that it is so modified as to be in useful relation to different environ- mental circumstances; as far as possible we have traced out the consequences, and have reached the conclusion that the change of behaviour must, on the one hand, lead to expansion, and on the other, to contraction ; MIGRATION COMPREHENSIVE 277 and we have seen that this conclusion is in accord with the facts of observation—that is the general result of our inquiry into the functioning of the two powerful impulses, the impulse associated with the disposition to secure a territory and the gregarious impulse. The phenomenon of migration embraces a number of separate problems, each one of which presents features of great interest and of still greater difficulty. On some of these problems I do not intend to touch; I seek only to ascertain whether the impulses that are con- cerned in the securing of a territory, and in the search for society, bear any relation to the problem as a whole. I hold that the origin of migration is not to be found merely in conditions peculiar to a remote past, but that the conditions inhere in the organic complex of the bird, and are thus handed down from generation to generation. Starting with this assumption I examined the behaviour which normally accom- panies the seasonal life-history of the individual, and found, in that behaviour, manifestations of cyclical change leading to definite biological consequences. I now propose to inquire whether those consequences are such as might, in the course of time, give rise to the seasonal change of abode. We are apt to think of migration in terms of the Warbler that enlivens our hedgerows in the spring after travelling hundreds of miles from the south, or of the Redwing that comes from 278 RELATION OF TERRITORY TO MIGRATION the far north and seeks its food during the winter on the meadows, or perhaps of the American Golden Plover that each year covers a vast expanse of ocean in its journey from its breeding ground. The length of the distance strikes the imagination and constrains us to focus attention upon the extremes. But migration is of much wider significance than is here represented. I sit beside the River Severn in April and watch Swallows, Tree- Pipits, and Yellow Wagtails passing in twos and threes, in small parties, or it may be in small flocks; and I observe that while some establish themselves in the neighbourhood, others pass on. Or I watch Herring-Gulls returning to the breeding station at Bolt Head, an endless stream of individuals coming from the east as far as eye can reach; following them for some miles inland I see them still, first as specks upon the horizon, then passing beside me as they beat their way slowly against the strong south-westerly winds, and finally disappearing from view in the direction of the cliffs. Or again, I watch Buntings and Finches deserting the flock and seeking stations in the marsh, or amongst the furze-bushes on the common, or in the spinneys. In each case the proximate end of the behaviour is alike—wherein then lies the difference? Only in the distance which separates the territory from the area in which the birds formerly associated. And intermediate between the extremes, I doubt not, if we had a sufficient body of observations, that we should INTERNAL IMPULSE 279 find numerous gradations, the lesser merging step by step into the greater. Is the Swallow a migrant and the Herring-Gull not; is the Tree-Pipit a migrant and the Bunting not; must a bird cross many miles of sea or of land before it can be considered a migrant; is the length of the distance traversed a criterion of migration? Surely not. The distance traversed is merely a collateral consequence of the process as a whole. | The annual life-history of a bird presents, as we have seen, two distinct phases—the one in which the individual dominates the situation, the other in which it is subordinated to the welfare of the community. Let us take these two phases separately and endeavour to see how they may have influenced the seasonal move- ments ; and first let us take the more important of the two, namely that one whiclr is directly concerned in the continuance of the race. In this phase we must consider the three factors to which allusion has already been made :—(1) the internal impulse, (2) the innate ability to return to the former breeding ground, (8) the conditions in the external environment. These three work in close relation and, as I shall endeavour to show, lead to important results. (1) If there were nothing in the inherited nature beyond an impulse to seek the breeding ground, if, that is to say, when the appropriate locality were reached, the bird took no further interest in the developing situation, the attain- ment of reproduction would become largely a poe: 280 RELATION OF TERRITORY TO MIGRATION matter of chance. A male in a congested district, having no incentive to seek fresh ground, would remain inactive until a female happened to cross its path and stimulate its sexual impulse, when its activity would take another form. Hence some districts would be over-populated, whilst others would remain unexplored. But the system of reproduction does not consist merely of a search for the breeding ground, and of the discharge of the sexual function; it is a much more complex business, yet withal more complete. Nothing is left to chance; the end is attained step by step; and each successive stage marks the appearance of some specific factor which con- tributes towards the success of the whole. We start with the appropriate organic condition under which, when adequate stimulation is provided, the disposition to secure a territory comes into functional activity. Within the field of this disposition we can distinguish certain specific impulses. In sequential order we have the impulse to seek the breeding ground; the appropriate situation which gives rise to an impulse to dwell in it; and the act of establishment which supplies the condition under which the impulse to drive away intruders is rendered susceptible to stimulation. Grouping these impulses, for the convenience of treat- ment, under one general heading, I speak of an impulse to seek isolation. It implies some kind of action with some kind of change as its correlated effect; and from it there flows INNATE ABILITY 281 a ceaseless energy directed towards a definite end which for us, who can perceive its prospective value, is isolation in an appropriate environment. The emphasis here is on “isolation,” for it involves competition, and there cannot be com- petition without some change in the relative positions occupied by different individuals; so that in each recurring season there will be not only a re-arrangement of ground formerly occupied but an arrangement of ground formerly deserted. (2) That the older birds return to the locality wherein they had formerly reared offspring, and the younger to the neighbour- hood of their birthplace, was always deemed probable. But in recent years evidence which cannot be rebutted has been supplied by the marking of birds. This evidence, details of which can be found in the summary of results published annually by Mr Witherby in British Birds, demonstrates that the adult frequently returns not only to the same locality in which it formerly bred, but even to the same station ; that it does so year after year; that this mode of behaviour is not peculiar to one sex; and that many of the young breed in the locality in which they were reared. Such being well- established facts, we can infer the existence of an innate ability to revisit the place wherein the enjoyment of breeding, or of birth, had formerly been experienced. Of its nature we know little or nothing. It would almost seem as if there must be some recollection of past 282 RELATION OF TERRITORY TO MIGRATION enjoyment, but all that can be definitely asserted is —that past experience somehow becomes ingrained in the life of the individual and determines present behaviour. What, however, is of importance to us at the moment is not the ad hoc nature of the bird, but the biological consequences to which the behaviour leads. For if, on the average, individuals return to their former haunts, it follows that the annual dispersion will not be merely a repetition in this season of that which had occurred in a previous one, but that the little added this year will become the basis for further additions in the next. The innate ability is handed down from generation to generation, and, in so far as it contributes to success, is fostered and developed by selection ; and the modifications of behaviour to which it leads, since the results of prior process in the parent persist as the basis and starting - point of subsequent process in the offspring may in a sense also be said to be handed down. (3) The conditions in the external world may be organic or inorganic. By organic I mean the conditions which depend upon the number of competitors or enemies by which a bird is surrounded. The competitors may include other species which require a similar environment; and the enemies, species which prey upon it, or animals which take its young or its eggs. They vary in different seasons, in different districts, and in nature and extent—the success of one species leads to the failure of another, and the CONDITIONS IN ENVIRONMENT 283 multiplication of the Jay or of the Magpie robs us of many a songster. By inorganic I refer to the changes in the climate and in the surface of the earth. The nourishment of the young depends upon a regular supply of food, and the supply of food depends upon the climate which alters in different periods; in one decade the tempera- ture falls below, whilst in another it rises above, the normal, and, as the insect life fluctuates, so there is fluctuation in the bird population. The changes in the surface of the earth are manifold. Little by little the alder (Alnus glutinosa) overspreads the marsh. Young shoots spring up here and there, in a few years grow into bushes, and in a few more years are trees; and the dense masses of rush which seemed to choke their growth, yielding their position of importance, slowly disappear. And where formerly the Orchis latifolia, Orchis mascula, and Juncus communis grew in mingled confusion, nothing but water, moss, and the spreading roots of alder cover the ground. As the rush disappears, many birds that for generations have inhabited that marsh must seek accommodation elsewhere. Ancient breed- ing haunts thus disappear, new ones come into being, and even those which appear to be permanent are almost imperceptibly changing. Now the bird inherits a nervous system, which works under internal excitation and external stimulation. Given the appropriate organic condition and adequate stimulation, 284 RELATION OF TERRITORY TO MIGRATION and the impulse to seek isolation comes into functional activity. What the organic condition is and how it arises we do not exactly know; all we know is that organic changes do take place in the breeding season, that these changes profoundly modify character, and that they correspond with the seasonal growth of the sexual organs. And with regard to the question of stimulation, we have again to confess to much ignorance, although certain facts are pre- sented to observation which seem to indicate the direction in which the stimulus lies. For example, it is well known that abnormal climatic conditions influence behaviour ; we see migrants retracing their flight along the very course they travelled a short time previously—driven head- long by the blizzard, that at least is what we say. But if the wind, instead of being cold and from the north, is warm and from the west, do they retrace their flight? I have not found it so. And if there be no wind and the tempera- ture is low, are they still affected? Again, I have not found it so. When, as we commonly say, they fly before the storm, some change takes place in their organic complex, some new impulse receives stimulation or the former one lacks it. If, after Lapwings have established themselves in their territories, the weather becomes exceptionally severe, the birds collect together again in flocks and revert to their winter routine ; and under similar circumstances, Buntings fail to sing and temporarily desert their territories. In such cases it is clear that ISOLATION LEADS TO EXPANSION = 285 the impulse to seek isolation ceases for a time to dominate the situation. The inference, there- fore, is that atmospheric changes bear some relation to the functioning of the instinct; but whether it be temperature, or humidity, or the direction and velocity of the wind, or a combina- tion of two or more of these factors that supplies the stimulus, we cannot tell. The appropriate organic condition and the stimulus have then still to be determined, and we must pursue our inquiry from the point at which the impulse comes into functional activity. We will take a simple case, and one free from complication. Let us suppose that there is an area bereft of bird life, if it can be so imagined, but in proximity to other inhabited areas. Into this area, whilst in search of isolation, let us imagine that a Yellow Bunting finds its way. After the manner of its race it establishes a territory and occupies, let us say at a low computation, half an acre of ground. It then obtains a mate, breeds, and rears offspring, two of which we will assume are males. Reproduction ended, the birds desert the area, and in the following spring, when the impulse again asserts itself, parents and offspring seek again their former haunts. We now have three males, each of which occupies half an acre, and each of which rears two offspring—that is the position at the close of the second year. In the third year the number will have increased to nine and the area occupied to 45 acres; and so on in succeeding years, until by the beginning of 286 RELATION OF TERRITORY TO MIGRATION the eleventh year, we have 59,048 Yellow Buntings occupying 29,5243 acres or 46 square miles. This, then, will be the result of the operation of the impulse, providing that all the individuals survive and that no complications supervene. But of course complications are numerous, some of which retard while others accelerate the rate of expansion. These complications arise from various sources—in the first place from natural enemies which prey upon the birds or upon their eggs; in the next place from climate which, if it happens to be unfavourable, may mean that food is scarce and that only a small percentage of the young survive; and lastly from rivals—and by rivals I mean closely related forms that require a similar station and similar food—which, by occupying available ground, may check expansion, or, by forcing a continua- tion of the search, may widen it. Now when individuals fail as many do fail in their initial attempt to secure territory, the activity of the impulse still persists, and there is no control over the direction in which the bird continues to wander whilst in search of its end. Some therefore seek in this direction, others in that ; some wander inwards into inhabited areas and fail to find accommodation, or, according to the relative strength of their impulse, perhaps succeed and so set free a new competitor, others wander outwards into country unin- habited by the species. These latter we will call “pioneers.” They may find accommoda- ISOLATION LEADS 'TO EXPANSION = 287 tion within a comparatively short distance of their base, or they may come into competition with rivals and fail, not necessarily on account of any congenital weakness of ability, but because, being warned by an alien song, they may be precluded from coming into contact with just the environing conditions which can supply the stimulus and allow behaviour to run its further course—and so be obliged to extend their search into remoter districts. But it must not be overlooked that they will be placed in a most advantageous position so far as the attain- ment of reproduction is-concerned. In their search for territory they will meet with little opposition and will be free to select whatsoever ground they will; and be free also from intrusion by neighbouring males, which is so frequent in occurrence and continues for so long in congested areas. Moreover, in thinly populated districts, the pressure upon the available means of support will not be so great, neither will natural enemies be so plenti- ful; and since the offspring, guided by prior experience, return to the neighbourhood of their birthplace, the advantages thus gained will be shared by the succeeding generation. It follows, then, that the range of a species will not always be continuous, will not, that is to say, proceed by a series of successive steps, but that sometimes in this direction and at other times in that, the chain of territories will be interrupted and different individuals separated by distances of greater or lesser 288 RELATION OF TERRITORY TO MIGRATION extent. New colonies will thus come _ into being; and as the unlimited increase of the population over limited areas gradually reintro- duces into them the struggle for territory, new centres of distribution, where the process will repeat itself and from which expansion will proceed afresh, will be formed. Hence, though it is clearly impossible for the progeny of one pair of Yellow Buntings to overspread the whole of the 46 square miles, it is by no means impos- sible for the limits of their range to exceed even those limits within the eleven years. To sum up our knowledge regarding this phase. Of the organic condition which renders the impulse responsive to stimulation we know very little; and though certain facts of observa- tion seem to indicate the direction in which the stimulus is to be found, we must here again confess to much ignorance. So far as can be seen, however, the impulse to seek isolation with its correlative territory, leads to constant modification in the breeding range of most species. The occupation of the small space of ground which each individual requires, the extent of which has been gradually adjusted to suit the needs of different species, results in expansion not only in one direction but in every direction, and not only in one season but in every season. And if there were no complications in the external world this expansion would proceed, as we have seen, with astonishing rapidity. But complications, some of which are favourable and others unfavourable, are numerous, and it is 4 EFFECT OF THE GREGARIOUS INSTINCT 289 | difficult to estimate their importance or to indicate their precise effect; the former, how- ever, accelerate the rate of expansion, whilst the latter retard it. Those individuals that wander outwards and seek territory on the outskirts of the range we have called “pioneers.” They will have advantages over others that, wandering inwards, seek isolation in congested districts, and will succeed where the latter fail; and since there is in the young an innate ability to return to the district wherein they were reared, the advantages so gained may be said to be handed on from generation to generation. Let us now turn to the contra-phase, and endeavour to ascertain whether the gregarious instinct bears any relation to the seasonal desertion of the breeding ground. The conclu- sion at which we have already arrived regarding this instinct is that it forms part of the inherited nature of most species; that its functioning is suppressed when a bird is actually in occupation of a territory ; and that it is serviceable in pro- moting the welfare of the individual. We cannot of course observe the instinct. What we observe, when reproduction is ended, is a change in the relations of different individuals ; instead of arousing mutual hostility, they attract one another, from which we infer the existence of something which determines their conduct, and this “something” we speak of as an instinct. To what does this change lead? Let us suppose that there is an area inhabited by one 290 RELATION OF TERRITORY TO MIGRATION species; that the number of inhabitants has reached the maximum that the means of sustenance will allow; and that the season of reproduction is drawing to a close. The position will then be as follows. All the available breeding ground is divided into terri- tories; each territory is occupied by one unit, the family, and each individual is able to fend for itself; changes both internal and external begin to take place, the gregarious instinct comes into functional operation, and the supply of food diminishes—that roughly is the position. The internal factor operates so that the sight of this individual or the call of that, instead of evoking hostility as heretofore and keeping different units apart, proves now an irresistible attraction; so that in place of a number of individuals evenly dispersed over the whole of this area, a small number of flocks of various dimensions are stationed at certain points, which points are determined partly by experience, partly by the supply of food, and partly by accident. ‘This implies for each individual some movement in some direction. But since the population of this imaginary area has reached the maximum, and the supply of food, though limited in distribution, is nevertheless plentiful, such movements will be irregular and will pro- ceed in no definite direction. Now let us suppose that the breeding range extends and that fresh ground is occupied by pioneers. When reproduction and the rearing of broods are ended and the gregarious instinct EFFECT OF THE GREGARIOUS INSTINCT 291 becomes dominant, these pioneers, or at least some of them, will revisit the area wherein formerly they associated with companions. Their offspring, however, though they will have the inherited impulse and the innate tendency, will not have the experience; how then will they behave? There can be no doubt that some will accompany the older birds, and, being led by them, will share the experience of a former generation; nor any question that others will collect together in the neighbourhood of their birthplace and, if their impulse is satisfied, will remain there so long as food is to be found. Thus the gregarious instinct, work- ing in close relation with acquired experience, will on the one hand lead to the formation of organised movements in certain directions, whilst on the other it will lead to the formation of new areas of association which will follow in the wake of the expansion. We have assumed, in the imaginary case which we have just taken, that the conditions in the external world are such as enable the birds to endure throughout the year—in short, that there are no complications regarding the supply of food. But we must bear in mind that so long as conditions are favourable during the period of reproduction, which is of short duration, the breeding range can continue to expand, and that therefore, in the course of centuries, regions will come to be occupied wherein, owing to alternations of climate or physical changes in the surface of the earth, U 292 RELATION OF TERRITORY TO MIGRATION food will be impossible, or at any rate difficult to obtain at certain seasons. Hence there will come a time when the area of association ceases to follow in the wake of the expansion, and the breeding area begins to diverge from the subsistence area. How, then, is the gulf between these two areas to be bridged? We can of course say that those individuals which, in virtue of some slight variation of hereditary tendency, return to regions where food is plentiful will survive ; whilst others, less well endowed, will perish. We can state the position in some such general terms, and doubtless there would be truth in the statement, but it does not carry us far; we wish to know more of the nature of the tendency, and of the manner in which it has evolved. Well now, in this new situation which arises, two things are apparent—that the struggle for existence becomes a struggle for the means of subsistence, and that anything in the inherited constitution of the bird which can be organised to subserve the biological end in view becomes of selection value. So long as food can always be procured in the new areas of association, the individuals that behave in accordance with ancestral routine gain thereby no particular advantage; but directly the breeding range extends into regions where the supply fluctuates, traditional experience becomes a factor in survival, and those indi- viduals that come under its influence will, on the average, be more likely to endure and so EFFECT OF THE GREGARIOUS INSTINCT 293 to procreate their kind and maintain the tradition. Let it once be granted that there is an innate capacity to retain in later phases of routine the experience gained in earlier phases, and it is difficult to see how traditional guidance can be refused recognition as a factor in the developing situation. But only a factor, and by no means the most important one; for observation has shown that the young are capable of performing the return journey without guidance. Something therefore is inherited, some impulse which comes _ into functional activity at a specified time, and leads the bird to set forth in a given direction. There are no grounds for supposing that _the experience of one generation forms any part of the hereditary equipment of subsequent generations. In what direction then are we to look for the congenital factor? What is given is an inherited tendency to co-operation and mutual help, and an innate capacity to make use of the results of experience. The inherited tendency, as we have seen, leads on the one hand to the formation of new areas of associa- tion, whilst on the other, since it is the means of bringing isolated individuals into contact, it leads to experience being handed on from generation to generation, which, in its turn, results in a certain amount of backward move- ment along the line of expansion. It forms part of the hereditary equipment of many species, and is serviceable in promoting the welfare of the individual. Moreover, there is U2 294 RELATION OF TERRITORY TO MIGRATION reason to believe that its origin dates back to an early period in the evolution of the higher forms of life; and if in the subsequent course of evolution it could have been so organised as to serve a double purpose, so much the more reason would there have been for its survival. In what does the instinct consist? Is it merely that the sight of this individual or the call of that proves at some particular moment an irresistible attraction, or does the appropriate organic condition give rise, as is generally supposed, to some preceding state of uneasiness ? In the former case, the temporarily isolated individual or colony would have but little chance of sharing in the benefits which mutual association confers upon the associates; in the latter, the feeling of discomfort would lead to restlessness, and would thus bring the bird into touch with the environing circumstances under which instinctive behaviour could run_ its further course. So that it is probable that the movements of each individual, prior to its becoming a unit in the flock, are not accidental but are determined in some measure by racial preparation. Now if the fundamental assumption of the doctrine of the struggle for existence be true, the gregarious instinct will not be quite alike in all the members of different broods, nor even in each member of the same brood; that is, variation will occur in all possible directions. And we shall not, I think, exceed the limits of probability if we assume that different individuals EFFECT OF THE GREGARIOUS INSTINCT 295 vary in the persistency with which they strive to attain their unknown end, and in the direction in which they travel in pursuit of it. So that in each generation they will fall into three classes: _ (1) those which are inert, (2) those which wander along the line of expansion, (38) those which wander in other directions. If then the struggle for life at this particular juncture in the evolution of the breeding range is a struggle for the means of subsistence, the members of these three classes will not be in a like satisfactory position so far as the competition for food is concerned. ‘Those in the first class—z.e., those in which the activity feelings are weak—will neither gain the benefits which arise from mutual help, nor will they have much prospect of enduring through the season of scarcity. Those in the third class will, it is true, derive some assistance one from another, and so be in a better position to discover what food may be available; but inasmuch as they will remain in regions where the climate alternates and the supply of food is liable to fall below the minimum required, the chances are that a high percentage will fail in the struggle for existence. We come now to those in the second class, and it is upon them that I wish more particularly to focus attention. The initial movement in their case will be in the direction from which outward expansion has all along taken place. Within a comparatively short distance they will reach districts where the species is plentiful, and here, associating with others that have some traditional 296 RELATION OF TERRITORY TO MIGRATION experience, they will be guided by them and will find themselves in regions where food is plentiful. Hence in each generation those will survive that, owing to some congenital variation of their instinct, seek satisfaction for their impulse in a direction which brings them under the influence of tradition. And though at first but slight and not in themselves of survival value, such variations, since they coincide with modifications of behaviour due to acquired experience, will be preserved and in the process of time so accumulated as to be capable of determining the direction and extent of the movement. But the young Cuckoo deserts this country many weeks after its parents, and there is no reason to suppose that it lives in society when eventually its destination is reached; and the young Falcon passes to the south, and is certainly not gregarious—how then can we explain their behaviour in terms of something which they show no signs of possessing? I do not wish to make light of a difficulty which admittedly, at first sight, is a grave objection to the view that the gregarious instinct has been operative in the manner here claimed for it. It must, however, be borne in mind that this instinct, though originally developed to serve the purpose of mutual protection, supplies the material upon which evolution works when the extension of the breeding range creates a situation requiring readjustment on the part of the organism to new conditions of life; and that SUMMARY 297 those variations which can be so modified as to be in useful relation to the new environmental circumstances are seized upon by natural selection and, being transmitted, form the foundation of a specific inherited response, no longer dependent upon, though operating in close relation with the primitive response whence originally it sprang. Thus the primordial instinct becomes so organised as to serve a secondary purpose, that of rendering secure a means of access to a certain food supply. In the course of evolu- tion species were bound to arise which, owing to some peculiar conditions, derived greater advantage from living solitary than from living in society. Does it then follow, because such species manifest no inclination to live in society, that the instinct never has played any part in their lives? Or because the primary purpose has lapsed, does it follow that the secondary no longer exists ? Let me recapitulate the principal considera- tions which I have discussed in this chapter. Though I have been advancing a theory, and though I have taken much for granted, yet it will, I think, be admitted that both the theory and what has been taken for granted rest on observational grounds. As our starting-point we have a bird whose inherited nature alternates according to the season, and in whose nature we ean distinguish two contra-phases—the one to live in society, the other to live solitary. While both have their part to play in furthering the U3 298 RELATION OF TERRITORY TO MIGRATION life of the individual, for biological interpretation there is only one end, the prospective value of which is the continuance of the race. We may say that the latter phase is the more important of the two because it is directly concerned with reproduction. But we shall make a great mis- take if we attach peculiar importance to one phase, or to one mode of behaviour within that phase, or to one action within that mode of behaviour ; for if there is one thing certain it is that the whole is an inter-related whole in which each part depends for its success upon that which precedes it. In that phase in which the territory is the central feature of the situation, the struggle for existence is in operation in its acutest form ; all the congenital and acquired capacities of the bird — pugnacity, song, capacity to utilise in later phases the experience gained in prior phases, all these are organised to subserve an end—a proximate end—which in its simplest terms may be described as “isolation.” Isolation is then the first step in the process of reproduc- tion, and any individual that fails to make it good, fails to procreate its kind. But isolation implies separation, and the degree of separation varies in different species, from the few square feet of cliff required by the Guillemot to the few square miles of barren moor over which the Peregrine exercises dominion. One species must occupy sufficient ground to enable it to secure food for its young; another requires sufficient, but no more, upon which to deposit its egg ; and SUMMARY 299 a third must secure a position for its nest within the community. Hence it follows that the degree of separation varies with the conditions of existence. Since, however, the conditions in the external world are constantly changing according to the relative abundance or scarcity of enemies, the rise or fall of rivals, the physical changes in the earth’s surface, and the alterations of climate, it is clear that isolation can only be obtained with difficulty, and that the competi- tion for it must be severe. Some individuals therefore fail to breed, whilst others, perhaps because their impulse is stronger, persevere and seek stations elsewhere. What are their prospects of finding them? By extending the field of their activities, they will wander into districts remote from the scene of competition, districts where not only food is plentiful but where enemies and rivals are scarce; and to these pioneers, if to any, success in reproduction will most certainly be assured. But not only is it they who will benefit; their offspring also, when the time comes for them to take their part in the maintenance of the race, will share in the success of their parents, for even though they may not escape competition from individuals of closely related forms, they will meet with but little from those of their own kind. Now species which live throughout the year in the vicinity of their territory are comparatively few, the majority are obliged to wander in search of food so soon as reproduction is ended, and their behaviour is determined not only by its 300 RELATION OF TERRITORY TO MIGRATION abundance or scarcity, but also by the powerful gregarious impulse which waxes in proportion as the instincts connected with reproduction wane. If, then, when the sexual instinct again becomes predominant, the experience of the former season nowise affects their movements, little or no progress will be made in the expan- sion of the range. But just as a certain entrance into the bush and pathway through it, when once made use of in the process of building, becomes so firmly established as to form the sole highway to and from the nest, so likewise, when the impulse to seek isolation repeats itself, the bird is constrained to seek the neighbourhood wherein it had experienced the enjoyment of breeding or of birth. Thus the little that is added one year becomes the basis for further additions in the next, and new centres of distribution are continually being formed from which expansion proceeds anew. Now as the range gradually extends into regions where the climate alternates and food at certain seasons is consequently scarce, the distance between the customary area of associa- tion and that of reproduction must perforce widen. ‘The question then arises: How will the young that have no experience find their way to regions wherein they can endure? The forces which may have been organised to subserve the end in view are three: (1) Acquired experience, (2) tradition, (8) the gregarious instinct. The pioneer that carries the range a little further forward starts from a base where it has associated SUMMARY 301 with companions and found food plentiful; and when the impulse to live in society again asserts itself, it not only repeats its former experience but hands on the habit thus acquired to thése of the next generation that happen to accompany it. Granting, however, that by successive increments in the distance traversed, traditional guidance may in time accomplish much, it cannot account for all the known facts, it cannot at any rate explain the fact that in some cases the inexperienced offspring finds its way to the food area without guidance. Something, therefore, 27s inherited. And my suggestion is this: That the gregarious instinct, the ancient origin of which we can infer from its manifesta- tion in so many and diverse forms of life, supplies the material upon which evolution works ; that variations of the initial impulse, at first slight and not in themselves of selection value, in so far as they coincide in direction with modifications of procedure due to experience or tradition, are preserved ; and that, in the process of time, they are so accumulated as to form a specific congenital endowment determining a definite mode of behaviour. INDEX ACQUIRED experience, 300 Adjustments, transitory, of dis- tribution, 275 Alarm notes, 119 Arrival, advantages and dis- advantages of late, 33-44 Assemblies in winter, 262, 263 Assembly grounds, 173 Attainment of reproduction, 171 BARRINGTON, R. M., on the sex of migrants, 25 Battle between Cuckoos, 82 — between two Moor-Hens, 86, 92, 93, 94 — — Pied Wagtails, 86 — — Raven and Buzzard, 217 — — Raven and Peregrine, 216 law of, 13, 19 Behaviour routine, 262 — sexual, 3 Bickerings, 96 Birthplace, return to, 43, 50 Blackbird, 87, 182, 222, 244 Blackcap, 81, 156, 224, 230 Black Grouse, 63 Black-tailed Godwit, 53 Boundaries, 1, 5 — conflicts for retention of, 7, 62 — disputes as to, 1 802 two male Brambling, 124 Breeding ground, search for appropriate, 270, 271 — range, extension of, 291-92 — site, acquirement of, 3 — stations, evolution of, 15-19 —--repeatedly visited long before nesting-time, 64 — territory, 2, 3, 7 — — evolution of, 18 — — foundation of, 7 — — innate capacity to return to former, 279-81 Bridled Guillemot, 64 Brooding, 180 — impulse, 191 Bunting, Cirl, 28, 140 — Corn, 28 — Reed, 28, 68, 69, 85, 104, 132, 158, 160, 244 — Yellow, 28, 30, 47, 64, 140, 159, 162, 183, 187, 188, 189, 235, 236, 286 Buzzard, 217 CAPACITY, innate, to return to former breeding territory, 279-81 Carrion Crow, 226 Chaffinch, 28, 31, 32, 33, 45, 87, 103, 156, 159, 235, 236, 244 — Donegal, 160 INDEX Change of breeding quarters owing to unsuitableness, 50 Chiffchaff, 49, 51, 80, 139, 140, 221, 224, 244 Cirl Bunting, 28, 140 Clarke, W. Eagle, Studies in Bird Migration, 24 Cleanliness of nest, 180 Cliff-breeding species, 63 Climatic changes, alteration of routine, due to, 284 — changes, food dependent on, 283 — conditions, influence of, 20 Communities, 202 —pbirds after breeding-season remain in, 265-67 Competition, female, for males, 13 Complexity of strife, 84-85 Conflicts between males during the mating period, 74, 86 — between males during the nesting period, 87 — for areas, 10, 11, 13, 62 — of Ruff, 54 — sexual, 10 Congenital disposition, 135 Contests between males for possession of females, 80 Coot, 61 Corn-Bunting, 28 Corncrake, 39 Crow, Carrion, 226, 227 Crow, Hooded, 202 Cuckoo, 52, 82, 144, 296 — restricted breeding area, 52 Curlew, 119, 138, 140, 250, 262, 263, 265, 273 DANGER warnings, 269 Darwin, C., Descent of Man, 35 — on the arrival of males be- fore females, 35 303 Defence of territory, 6 Development, sexual, 6 Disposition, congenital, 135 — functioning of, 74 — inherited, 5 —to defend the territory, 73-118 — to mate, 27 —to remain in a particular place in a particular en- vironment, 6 — to secure a territory, 6, 20-72 Distribution, adjustment of, 275 Dove, Turtle, 126, 232 Dunlin, 250 EmotionaL behaviour, 53, 82, 114 — manifestation, 90, 263 — response, 26 Enemies, 282 Energy, waste of, 219 Environment, 6 — and food, 56 — changes of, 283 — external, conditions in, 279, 982 © Equipment, hereditary, 6 Evolution of breeding stations or territory, 15, 19 — of the territory, 176 — of the voice, 163 Existence, struggle for, 294 Experience, acquired, 300 Experiments, removal of nests for, 181, 185, 190, 213, 214 Exposure, its effect on nestlings 180 External environment, ditions in, 279, 282 con- Fatcon, 48, 71 Feeding grounds, neutral, 125 in communities, 70 304 Females, fighting amongst, 109- 118 — sexual impulse of, 13 Fieldfare, 124 Fighting instinct, 79, 82 Flight, emotional behaviour of Godwit during, 53 Flocks, in winter, birds collect together in, 262 Flycatcher, 244 Food, procuring of, 5 — abundance, or scarcity of, its relation to prosperity of young, 15, 16 — its bearing, on the movement of flocks, 262 — rearing of young dependent on rapid and regular, 179, 195 — supply, proximity to, neces- sary for rearing young, 179, 195 Fortuitous mating, 174 Fowler, Ward, on the value of communities, Rooks, 202 Fulmar, 121, 247 Functional activity, 259 — instinct of Reeve, 173 Functioning of the disposition, 275 — of the primary dispositions 100 GARDEN Warbler, 223, 225, 230 Giitke, H., Birds of Heligo- land, 24 —on the absence of song in birds on Heligoland, 124 —on the early arrival of Guillemots on Heligo- land, 64 Godwit, emotional behaviour of, during flight, 53 — Black-tailed, 53 INDEX Grasshopper Warbler, 39, 131, 139, 153, 155, 187, 244 Greenfinch, 28, 33, 140, 235, 236 Gregarious instinct, 20, 61, 141, 265-66, 269, 276, 289, 290, 291, 296, 300 Grouse, Black, 63 Guillemot, Bridled, 64 — Common, 63, 64, 121, 192, 195, 206, 211, 247 — Ringed, 64 Gull, Common, 119 — Herring, 210, 278 Hazir formation, law of, 8, 62, 65, 66, 67, 205 Hawfinch, 28 Headquarters, 176, 206, 207, 274 — restricted, 8, 9, 30, 50, 58, 64, 127 Hedge-Sparrow, 213, 221, 244 Hereditary equipment, 6 Herring-Gull, 210, 278 Hooded-Crow, 202 Hostility and territory, re- lationship between, 242 House-Sparrow, 218. IMITATION, vocal, powers of, 156, 157, 161 Impulse, internal, 279 — to brood, 191 Inherited disposition, 5 Instinct, fighting, 79-82 — gregarious, 20, 61, 141, 265, 266,'269, 276, 289, 290, 291, 296, 300 — mnigratory, 37 — of song related to establish- ment of territory, 125 — sexual, reawakening of, 4,18 Instinctive response, 180 Instincts susceptible to stimula- tion, 259 Internal impulse, 279 INDEX Internal stimulation, 62, 123 Interpretation of battles, '75 Intolerance of other birds, 218, 219 Intrusion resented, 274 Isolation; impulse to seek, 288 — of male, 12, 62, 65, 73, 81 —of male during breeding season, 267,272,273, 275,281 JAY, 87, 156, 283 KESTREL, 228 Kittiwake, 116, 200, 247 LAPWING, 58, 59, 61, 62, 64, 84, 103, 104, 126, 189, 190, 220, 251, 284 Lapwing, life-history of, 58-61 Late arrival, advantages and disadvantages of, 33-44 Law of battle, 74, 75, 86 Lesser Whitethroat, 230, 244 Linnet, 156 M‘Doveatt, Dr, Soczal Psycho- logy, 77 Magpie, 219, 283 Males arrive before advent of females, 24 Marsh-Warbler, 39, 40, 52, 81, 132, 140, 153,-155, 156, 165, 225 Martin, 201, 218 Mating, difficulties of, 172 — fortuitous, 174 Maximum number supportable in a given locality, 49 Meadow-Pipit, 188 Meeting places for antics, 54, 63 Mental Image, 77 Merlin, 227 Migration, 3-4 — distance no criterion, 279 — its relation to territory, 259 305 Migration, origin of, 260, 277 — phenomenon of, 277 Migratory instinct, 37 — species more highly special- ised than resident species, 56 Missel-Thrush, 21 Mobility of the land and stability of the water, 260 Moor-hen, 61, 85, 103, 218, 250, 251 Morgan, Professor Lloyd, on instinctive behaviour, 74 — on emotional behaviour, 114 Nest, cleaning of, 180 — construction of, 3 Nests, removal of, for experi- ments, 181, 185, 190, 213, 214 Neutral feeding grounds, 62, 125 — ground, 98 Newton, E., on the arrival at breeding stations of males before female, 24, 35 Nightingale, 39, 156 Notes of alarm, 119 — of anger, 119 — of recognition, 139 —of warning, 119, 139, 141, 145, 151, 153 OFFSPRING, rearing of, 3, 4 Organic change, sexual, 92, 123 — changes, 65 — condition of Reeve, 173 Owl, Wood, 156 PatreED for life, 55-56 Parental instinctive response, failure of, 185 Partridge, 87, 218 Persecution, Carrion Crow and Magpie, 226 306 Persecution, Carrion Crow and Rook, 227 — House Sparrow and Martin, 218 — Lapwing and Snipe, 220 — Raven and Buzzard, 217 — — and Peregrine, 216 — Starling and Woodpecker 218, 237 Persistency to remain in terri- tory, 68 Pied-Wagtail, 86, 155 Pigeon, Wood, 219 Pipit, Meadow, 188 — Tree, 51, 188, 189, 222, 244, 278 Polyandrous females, 144 Predatory species, 268 Promiscuous pairing of Ruffs, 172 Proximity to food - supply necessary for rearing young, 179, 195 Psychology, Manual of, 1 Puffin, 63, 116, 200 Pugnacious instinct, 87-109 Pugnacity, 11, 62 — of females to obtain mates, 109-118 —of males, prior to mating- season, 77-81 — of Moor-Hen, 218 ’ RactaL preparation, 41, 43, 46, 67, 205, 206, 266 Rail, Water, 218 Raven, 48, 202, 216 Razor-bill, 63, 64, 200, 247 Readjustment of territory, 146 Rearing of offspring, 3, 4 Red-backed Shrike, 39, 50, 51, 156 Redbreast, 47 Redshank, 139 Redwing, 124 INDEX Redstart, 230, 244 Reed-Bunting, 28, 68, 69, 85,104, 132, 156, 158, 160, 244, 246, 273 Reed- Warbler, 49, 51, 68, 81, 132, 140, 152, 153, 211, 225 Reeve, 171 Relation of song to the terri- tory, 119-68 — of territory to migration, 259 — of territory to the system of reproduction, 169-214 Relationship to a territory, 169 Reproduction, 14, 15 — and territory, 169-214 — attainment of, 2, 6, 37 — goal of, 6 Ringed Guillemot, 64 Robbery of territory, 104-107 Rock-formation, suitability, for Guillemots nesting on, 196 Rook, 202, 227 Routine behaviour, 262 Ruff, 54, 63, 172 — meeting placesfor conflicts, 54 Ruffs, promiscuous pairing of, 172 Savi’s Warbler, 139 Sedge-Warbler, 25, 44, 152, 226, 244 Selous, E., on the life-history of Ruffs and Reeves, 172 —on meeting places for con- flicts and antics, 64 —on the meeting places of Black Grouse, 63 Service, Robert, on flocks of unmated Sedge-Warblers, 44, 45 Sexual behaviour, 3 — conflicts, 10 — development, 6 — function, discharge of, 2, 3, 26 — impulse of females, 13 INDEX Sexual instinct in the migratory male, 26 — of Reeve, 173 — — reawakening of, 4, 18 — life of birds, 1 — maturity, males arrive at, before females, 36 — organic change, 92, 123 — selection, 166 Shag, 121 Shrike, Red-backed, 39, 50, 51, 156 Skylark, 188, 236, 244 Snipe, 153, 156, 219, 220 Sociability when not paired, 125, 126 Song, as an aid in searching for a mate, 12 — its influence on mating, 167 — origin of, 138 — relation to reproduction, 123 — relation to territory, 119-168 — volume of, influenced by age, seasonal sexual develop- ment, or isolation, 166 Song-Thrush, 222, 244 Sparrow, House, 218 Sparrow-Hawk, 269 Spring, at approach of, birds loose their shyness, 138 Stability of the water and mobility of the land, 260 Starling, 217, 218, 237, 251 Stimulation, internal, 62, 123 question of, 284 Stonechat, 87 187, 188, 189, 222, 233, 234 Stout, Dr, Manual of Psycho- logy, 1,77 Struggle for existence, 294 Susceptibility to position, 96 Swallow, 21, 156, 278 TERRITORY, 1, 5 — adjustment of, 10 307 Territory and _ reproduction, 169-214 — breeding, 2, 3, 7 — dates of acquisition of, 33 — defence of, 6 — desertion of, after rearing young, 276 — disposition to defend, 73-118 — disposition to secure, 6, 20-72 — establishment of, 74, 285 — evolution of, 176 — failure to secure, 286 — fights for, 10, 11, 13, 62 — ownership of, 189 — possession of, a stimulus to song, 136 — its relation to migration, 259 — its relation to reproduction, 169-214 — readjustment of, 147 — restriction of, advantageous for mating, 172 — restricted, 8, 9, 30, 50, 58, 64 — separate for male and female Cuckoo, 144 — song, its relation to the, 119-68 — temporary desertion of, 28 35, 58, 59 —and hostility, relationship between, 242 Thrush, Song, 222, 244 Tit, Blue, 221, 226 — Great, 221 — Long-tailed, 226 Tradition, 300 Tree-Pipit, 51, 188, 189, 222, 232, 244, 278 Turtle-Dove, 126, 232 Unton of sexes, 12 Ussher, H. B., on the hostility between Choughs and Hooded Crows and Choughs and Ravens, 227 308 Vocat Imitation, 156, 157, 161 Voice calls of Curlew, 263 Waeratn, Pied, 86, 155 — Yellow, 278 Wanderings from land, Guille- mots, 193 Warbler, Garden, 223, 225, 230 — Grasshopper, 39, 131, 139, 155, 187, 244 — Marsh, 39, 40, 52, 81, 132, 140, 155, 156, 225 — Reed, 49, 51, 68, 81, 132, 140, 152, 153, 211, 225 — Savi’s, 139 — Sedge, 25, 44, 152, 226, 244 — Willow, 25, 47, 50, 51, 80, 91, 140, 187, 211, 232, 244, 273 — Wood, 50, 51, 132, 221 Warfare between different species and its relation to the territory, 215-58 Warning notes, 119 — of danger, 269 Water Rail, 218 Wheatear, 25, 51 Whimbrel, 140 Whinchat, 39, 50, 51, 81, 222, 232, 233, 234, 244 INDEX Whitethroat, 25, 50, 68, 69, 124, 140, 182, 187, 189, 190, 213, 230, 244 — Lesser, 230, 244 Wild Duck, 250 Will, the, to fight, 102 Willow-Warbler, 25, 47, 50, 51, 80. 91, 140, 187, 211, 232, 244, 273 Winter assemblies, 262-63 Witherby, H. F., in British Birds, on the return to former breeding - ground, 281 Wood-Owl, 156 Wood-Pigeon, 219 Wood-Warbler, 50, 51, 132, 221 Woodpecker, Lesser Spotted, 237 — Great Spotted, 237, 238 — Green, 20, 71, 156, 208, 218, 237 Wren, 244 YELLow Bunting, 28, 30, 47, 64, 140, 159, 162, 183, 187, 188, 189, 235, 236, 286 Young die in nest from ex- posure, 184, 185 PRINTED BY OLIVER AND BOYD, EDINBURGH, SCOTLAND Ree = rags = = ee ee el - a enn ae ——— aie