Territory in Bird Life

by Henry Eliot Howard

Now all, I think, will agree that it must serve some biological purpose—this at least seems to be the conclusion to be drawn from the two outstanding features of "diversity" and "specific character"; and since the voices of different individuals of the same species vary, it has been suggested that, by creating a more effective pairing situation, it is serviceable in furthering the life of the individual. I do not propose at the moment to enquire whether this doctrine be true, but rather to direct attention to other ways in which the song may be useful.

Is the instinct susceptible to stimulation under all conditions during the season of reproduction, or only under some well-defined condition? This is the question to which we will first direct inquiry.

Song in its full development belongs, as we have seen, to the season of reproduction; it is heard at the dawn of the seasonal sexual process, and is the most conspicuous outward manifestation of the internal organic changes which ultimately lead to reproduction. These changes would appear, at first sight, to be the primary condition which renders the instinct susceptible to appropriate stimulation. But while this is true up to a point, in so far, that is to say, as organic changes are a necessary antecedent of all behaviour connected with the attainment of reproduction, closer acquaintance with the circumstances under which the instinct is allowed full play leads to the belief that they are not alone sufficient to account for the facts as observed. In order to arrive at a decision we must seek out the specific factors in the external environment with which "song" is definitely related.

Some birds cross whole continents on their way to the breeding grounds, others travel many miles, others again find suitable accommodation in a neighbouring parish—nearly all have a journey to perform, it may be short or it may be long. The flocks of Finches gradually decrease and we observe the males scattering in different directions in search of territories; we watch the summer migrants on their way—small parties halting for a few hours in the hedgerows and then continuing their journey, single individuals alighting on trees and bushes and resting there for a few minutes, and the constant passage of flocks of various dimensions at various altitudes; and we see Fieldfares, Redwings, and Bramblings slowly making their way from the south and the west to their homes in the far north. Occasionally we hear their song, not the emotional outburst customary at this season, but, except in isolated cases, a weak and tentative performance. Gätke speaks of the absence of song on the Island of Heligoland, and refers to the Whitethroat as one of the few migrants that enliven that desolate rock with their melody. On the other hand, many migrants that rest temporarily on the Isle of May sing vigorously.[5] But on the whole there is, I think, no question that the male whilst travelling to its breeding grounds, and, even after its arrival, whilst in search of a territory, sings but little—and that little lacks the persistency characteristic of the period of sexual activity. Yet, when a suitable territory is eventually secured, the nature of the bird seems to change; for, instead of being silent and retiring, as if aware of some end not fully attained, it not only makes itself conspicuous but advertises its presence by a song uttered with such perseverance as to suggest that that end is at length attained. Hence, in a general way, the instinct of song seems to be related to the establishment of a territory.

Now the subsequent course of behaviour tends to confirm this view. We have already had occasion to refer to the fact that the males of some species desert their territories temporarily and join together on ground which is regarded by the birds that associate there as neutral, and that they do so not merely for the purpose of securing food but because they derive some special pleasure from the act of association, and we shall find that the altered behaviour of the male when it leaves its territory to seek food or to join the flock is an important point for us just now.

Buntings desert their territories temporarily and collect in flocks on the newly sown fields of grain. Some of the males are single, others are paired, and accompanied, it may be, by their mates; they wander over the ground in search of food, uttering their call-notes from time to time, or, settling upon the hedges and trees surrounding the field, rest there and preen their feathers. But even though a male may be surrounded by other males, even though it may occupy a position where it is conspicuous to all around, even though, that is to say, it is apparently in contact with just those stimulating circumstances which will evoke a response when it returns to its territory, yet it makes no attempt to sing.

Lapwings, when they resort to the neutral ground, run this way and that in full enjoyment of one another's companionship, behaving as they do when they flock in autumn and winter. Specific emotional manifestation is, however, absent, and their actions seem to be in nowise affected by the powerful impulse which only a few minutes previously determined their conduct, for of the characteristic flight with its accompanying cry there is no sign.

Early in the season Turtle Doves often collect from the surrounding country at certain spots where their favourite food is abundant. The croak of this Dove—its true song—is a familiar sound during the summer, but in addition the bird has a sexual note characteristic of the race. I watched a flock of upwards of one hundred on some derelict ground approximately eight acres in extent. Here, in May, the birds were attracted by the seeds of Stellaria media which was growing in profusion. After 5 A.M. there was continuous traffic between this piece of ground and the surrounding neighbourhood, a constant arrival and departure of single individuals or pairs; and, as they fed, the sexual note could be heard in all directions. Now some of the males occupied territories close at hand, and one could watch their passage to and fro; yet in no single instance did I hear the true song uttered on the feeding ground, although the moment a male returned to its territory its monotonous croak could be heard, uttered moreover with that persistence which is so marked a feature of all song or of the sounds that correspond to it.

Thus it will be seen that, even after the internal organic changes have taken place, the instinct of song is not susceptible to stimulation at all times and under all circumstances, but only at certain specified times and under special circumstances which can be observed to correspond with the occupation of the territory.

In many species each male singles out within its territory some prominent position to which it resorts with growing frequency. This position is an important feature of the territory, and exercises a dominating influence on the life of the bird. I have referred to it as the "headquarters," and it may be a solitary tree or bush, an outstanding mound or mole hillock, a gatepost or a railing—anything in fact that supplies a convenient resting place so long as it fulfils one condition, namely that the bird when it is there is conspicuous. It need not, however, be a tree or a mound or indeed anything upon which the bird can perch, for there is reason to think that the soaring flight undertaken at this season by so many males, since it is generally accompanied by the specific sexual sound, answers the same purpose as the topmost branch of a tree.