CHAPTER V
THE RELATION OF THE TERRITORY TO THE SYSTEM OF REPRODUCTION
In the first two chapters I tried to show that the inherited nature of the male leads it to remain in a definite place at a definite season and to become intolerant of the approach of members of its own sex, and that a result is thus attained which the word "territory" in some measure describes. But the use of this word is nevertheless open to criticism, for it denotes a human end upon which the highest faculties have been brought to bear, and consequently we have to be on our guard lest our conception of the "territory" should tend to soar upwards into regions which require a level of mental development not attained by the bird. It is necessary to bear this in mind now we have come to consider the meaning of the territory, or rather the position that it occupies in the whole scheme of reproduction.
Relationship to a territory within the interrelated whole of a bird's life serves more than one purpose, and not always the same purpose in the case of every species. We have only to glance at the life-histories of divergent forms to see that the territory has been gradually adjusted to suit their respective needs—limited in size here, expanded there, to meet new conditions as they arose. Now some may think that the theory would be more likely to be true if the territory had but one purpose to fulfil, and that one the same for every species; and they may see nothing but weakness in the multiplication of ways in which I shall suggest it may be serviceable. But such an objection, if it were raised, would arise from a mistaken conception, a conception which, instead of starting with a relationship and working up to the "territory," sees in the "territory" something of the bird's own selection and thence works back to its origin. Holding the view that it is nothing but a term in a complex relationship which has gradually become interwoven in the history of the individual, I see no reason why the fact of its serving a double or a treble purpose should not be a stronger argument for its survival. I now propose to examine the various ways in which the territory may have been of use in furthering the life of the individual, and the circumstances in the inorganic world which have helped to determine its survival.
The purpose that it serves depends largely upon the conditions in the external environment—the climate, the supply of food, the supply of breeding-stations, and the presence of enemies. Hence its purpose varies with varying conditions of existence. But before we proceed to examine the particular ways in which it has been modified to suit the needs of particular classes of species, and the reason for such modifications, we must inquire whether there is not some way in which it has been serviceable alike to every species, or at least to a large majority of them.
Success in the attainment of reproduction depends upon the successful discharge of the sexual function; and the discharge of the sexual function depends primarily upon an individual of one sex coming into contact with one of the opposite sex at the appropriate season and when its appropriate organic condition arises. Now the power of locomotion is so highly developed in birds that it may seem unreasonable to suppose that males and females would have any difficulty in meeting when their inherited nature required that they should do so, still less reasonable to suggest that this power might even act as a hindrance to successful mating. Nevertheless, if we try to picture to ourselves the conditions which would obtain if the movements of both sexes were in no wise controlled, and mating were solely dependent upon fortuitous gatherings, we shall come, I fancy, to no other conclusion than that much loss of valuable time and needless waste of energy would often be incurred in the search, and that many an individual would fail to breed just because its wanderings took it into districts in which, at the time, there happened to be too many of this sex or too few of that. And as the power of locomotion increased and the distribution of the sexes became more and more irregular, so the opportunity would be afforded for the development of any variation which would have tended to facilitate the process of pairing, and by so doing have conferred upon the individuals possessing it, some slight advantage over their fellows.
What would have been the most likely direction for variation to have taken? Any restriction upon the freedom of movement of both sexes would only have added to the difficulties of mating; but if restriction had been imposed upon one sex, whilst the other had been left free to wander, some order would have been introduced into the process. That the territory serves to restrict the movements of the males and to distribute them uniformly throughout all suitable localities, there can be no question; and since the instinctive behaviour in relation to it is timed to appear at a very early stage in the seasonal sexual process, the males are in a position to receive mates before the impulse to mate begins to assert itself in the female.
We will take the Ruff as an example. According to Mr. Edmund Selous, pairing, in this species, is promiscuous—the Ruffs are polygamous, the Reeves polyandrous. Suppose, then, that upon this island of some few miles in circumference, whereon his investigations were made, the movements of neither Ruff nor Reeve were subject to control, that the birds wandered in all directions, and that the union of the sexes were fortuitous, would the result have been satisfactory? We must remember that the Reeve requires more than one Ruff to satisfy her sexual instinct; we must also bear in mind the possibility that the functioning of her instinct may be subject to some periodicity, and we ask whether, under these circumstances, accidental gatherings would meet all the requirements of the situation. Now, manifestly, she must be in a position to find males when her appropriate organic condition arises. But in the absence of any system in the distribution of the sexes, how could delay be avoided, or how could a uniform discharge of the sexual function be assured? There is, however, a system. In the first place, there are the assembly grounds to which the birds repair season after season; and then, on the assembly grounds, there are the territories, represented, as Mr. Selous tells us, by depressions where the grass by long use has been worn away, and each depression is owned by one particular Ruff. The assembly grounds have the effect of splitting up and scattering the birds, and the number of Ruffs at any one particular meeting place is limited by the territories; with the result that Ruffs fit to breed are evenly distributed and always to be found in certain definite places, and the Reeves know by experience where to find them.