Territory in Bird Life

by Henry Eliot Howard

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

Those who are accustomed to notice the arrival of the migrants are aware that the woods, thickets, and marshes do not suddenly become occupied by large numbers of individuals, but that the process of "filling up" is a gradual one. An individual appears here, another there; then after a pause there is a further addition, and so on with increasing volume until the tide reaches its maximum, then activity wanes, and the slowly decreasing number of fresh arrivals 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 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 certain amount of overlapping occurs. A truer definition of the order of migration would be as follows:—Some males arrive before others, and some females arrive before others, but on the average males arrive before females. This fact has long been known. Gätke 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, i.e., females and younger males; while finally only young birds of the previous year are met with." Newton alludes to it as follows:—"It has been ascertained by repeated observation that in the spring movement of most species of the northern hemisphere, the 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 Migration, makes the following statement:—"Another characteristic of the spring is that the males, the more ardent suitors, of most species, travel in advance of the females, and arrive at their meeting quarters some days, it is said in some cases even weeks, before their consorts." Some interesting details were given in British Birds[1] in regard to the 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 isolation, remained with the females and increased their opportunities for developing that mutual appreciation which, by some, is held to be a necessary prelude to the completion of the 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 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 environment of the male, it must be taken merely as an expression of opinion, though based in some measure upon a general observation of the behaviour of various species.

Before attempting to explain the difference in the times of arrival of the male and female migrant, let us examine the behaviour of some resident species at a corresponding period. My investigations have been made 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 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; otherwise the earlier symptoms of any disposition to secure a territory may quite possibly be overlooked in the search for its breeding haunts.

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

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