Territory in Bird Life

by Henry Eliot Howard

You will say, however, that these smaller migrants have no exceptional powers of flight; that they have besides just completed a long and arduous journey; and you will ask why they should be expected to wander, whether it is not more reasonable to expect that, in order to overcome their fatigue, they should remain where they settle. The Cuckoo is a wanderer in the wider sense of the term, and is gifted with considerable powers of flight. Upon arrival the male flies briskly from field to field, showing but little signs of weariness; yet we have only to follow its movements for a few days in succession to assure ourselves that the bird is no longer a wanderer; for just as the Warbler or the Chat moves only within a definitely delimited area, so the male Cuckoo, strange as it may seem, restricts itself to a particular tract of land. The area over which it wanders is often considerable and consequently it is not possible to keep the bird always in view, but inasmuch as the variation in the voices of different individuals is quite appreciable, identification is really a simple matter. If we cannot keep the bird in sight, we can trace its movements by sound and mark the extent of its wanderings, which by repetition become more and more defined, until a belt of trees here, or an orchard there, mark a rough and rarely passed boundary line.

Let us take another example from the larger migrants—the Black-tailed Godwit, a bird common enough in the Dutch marshes but no longer breeding in this country. On suitable stretches of marsh land, numbers will be found in proximity one to another after the manner of the Lapwing, each male occupying a definite space of ground wherein it passes the time preening, searching for food, or in sleep—though at the same time keeping a strict watch over its territory. Now the preference shown for a particular piece of ground, and the determination with which it is resorted to, is the more remarkable when we take into consideration the specific emotional behaviour arising from the seasonal sexual condition. This behaviour is expressed in a peculiar flight. The bird rises high in the air, circles round with slowly beating wings above the marsh, and utters a call which, as far as my experience goes, is characteristic of the performance. The air is often full of individuals circling thus even beyond the confines of the marsh, for a male does not limit its flight to a space immediately above its territory; but nevertheless careful observation will show how unerringly each one returns to its own position on the breeding ground, no matter how extensive the aerial excursion may have been. And so, when the males of the smaller migrants confine their movements to an acre of ground at the completion of their long journey, they are acting no more under the influence of fatigue than the Cuckoo, which keeps within certain bounds yet flies about briskly, or the Godwit which, though holding to its few square yards on the ground, executes most tiring and extensive flights above the marsh.

Of all the migrants, however, the behaviour of the Ruff is perhaps the most strange, and though it has long been known that these birds have their special meeting places where they perform antics and engage in serious strife, yet it is only within recent years that the primary purpose of these gatherings has been ascertained—that purpose being the actual discharge of the sexual function. Mr. Edmund Selous has carried out some exhaustive investigations into their activities at the meeting places, and he makes it clear that each bird has its allotted position. He says, for example, that "It begins to look as though different birds had little seraglios of their own in different parts of the ground," that "each Ruff has certainly a place of its own," or again that "this Ruff indeed, which I think must be a tender-foot, does not seem to have a place of its own like the others." Nevertheless it is only at the meeting places that they have their special positions; there is no evidence to show that each one has a special territory, wherein it seeks its food, as the Warbler has, and therefore some may think that we are here confronted with behaviour of a different order. But we must bear in mind that the process has been adjusted to meet the requirements of different species: the size of the territory, the period of its daily occupation, the purpose which it serves—these all depend upon manifold relationships and do not affect the principle. Why it has been differentiated in different circumstances we shall have occasion to discuss later; for the moment it is enough that at the end of its migratory journey each Ruff occupies one position on the meeting ground.

Now birds that are paired for life, whose food-supply is not affected by alternations of climate, have no occasion to desert the locality wherein they have reared their offspring, and so their movements, being subject to a routine which would tend to become increasingly definite, must in the course of time and according to the law of habit formation become organised into the behaviour we observe. Is it necessary, therefore, to seek an explanation of their tendency to remain in one place in anything so complex as an inherited disposition? Again, since we have to confess to so very much ignorance on so many points connected with the whole phenomenon of migration, may there not be some condition, hitherto shrouded in mystery, which might place so different a complexion on the corresponding aspect of migrant behaviour as to rid us, in their case also, of the necessity of appealing to an inherited disposition? Such questions are justifiable. And if the life-histories of other species gave no further support to our interpretation, if, in short, the evidence were to break down at this point, then we should be forced to seek some other explanation more in keeping with the general body of facts.

But far from placing any obstacle in the way of an interpretation in terms of inherited disposition, the behaviour of many of those residents which are not paired for life gives us even surer ground for that belief. Moreover in their case the initial stages in the process are more accessible to observation. I will endeavour to explain why. In the process of reproduction the environment has its part to play—whether in the manner here suggested, or indirectly through the question of food-supply, matters not at the moment. Now, migratory species are more highly specialised than resident species as regards food, and are affected more by variations of temperature, so that they can live for only a part of the year in the countries which they visit for the purpose of procreation. Hence the organic changes, which set the whole process in motion, must be coincident in time with the growth of appropriate conditions in the environment; for if it were not so, if the internal organic changes were to develop prematurely, the bird would undertake its journey only to find an insufficiency of food upon its arrival, and this would scarcely contribute towards survival. Definite limitations have therefore been imposed upon the period of organic change. But in the case of many resident species the conditions are somewhat different, for they remain in the same locality throughout the year, and a gradual unfolding of the reproductive process cannot therefore have a similarly harmful effect. Thus it comes about that the behaviour of the migrant, when it arrives at the breeding ground and first falls under observation, represents a stage in the process which, in the case of the resident, is only reached by slow degrees; and by closely observing the behaviour as it is presented to us in the life of the resident male, we not only gain a better insight into the changes in operation, but can actually witness the breaking down of the winter routine, stereotyped through repetition, by the new disposition as it arises.

The first visible manifestations, even though they may be characterised by a certain amount of vagueness, are therefore of great importance if the behaviour is to be interpreted aright; and in order to insure that none of these earlier symptoms shall be missed, it is necessary to begin the daily record of the bird's movements at an early date in the season. As a rule the second week in February is sufficiently early for the purpose, but the date varies according to the prevailing climatic conditions. Even in species widely remote there is great similarity of procedure, and the behaviour of the Buntings is typical of that of many. With the rise of the appropriate organic state the male resorts at daybreak to a suitable environment, occupies a definite position, and singling out some tree or prominent bush, which will serve as a headquarters, advertises its presence there by song. At first the bird restricts its visits, which though frequent in occurrence are of short duration, for the most part to the early hours of the morning; it disappears as suddenly as it appeared, and one can trace its flight to the feeding grounds—a homestead or perhaps some newly sown field. But by degrees the impulse to seek the society of the flock grows less and less pronounced, the visits to the territory are more and more prolonged, and the occupation of it then becomes the outstanding feature of the bird's existence. This in outline is the course of procedure as it appears to an external observer.

But although much can be learnt from the lives of these smaller species, there is no gain-saying the fact that a great deal of patient observation is required, and the process is apt to become tedious. There are others, however, which are more readily observed, whilst their life-histories afford just as clear an insight into the effect produced by the new disposition upon the developing situation; and among these the Lapwing takes a prominent position, because it is plentiful and inhabits open ground where it is easily kept in view.