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 environment 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 disposition 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 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 displayed 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 environmental 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; 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.