there is no possibility of too many congregating in this locality, and all the less likelihood of too few finding their way to that; and hence, on the average, different pairs are distributed throughout all suitable localities. Furthermore, owing to the fact of their having a headquarters, the male and female are allowed a freedom of movement which otherwise they would only possess when the construction of the nest had actually begun; they can seek their food independently, and, even though paired, they can if necessary continue their winter routine without risk of separation. This means that the organic condition which leads to pairing, is free to develop in the female earlier than would be the case if there were nothing in the external environment to attract the pair to a particular spot; and the longer the period over which the process of pairing can be spread, the greater chance will females have of discovering mates, the less severe will the competition tend to become, and, consequently, the smaller the percentage of individuals that fail to obtain suitable partners.
In these ways the territory has been serviceable alike to a number of species. But much as the questions of mutual discovery and regular distribution may have influenced the course of its development, there can. I think, be little doubt that, on the one hand, the supply of the necessary accommodation for rearing offspring, and on the other, the necessity for an adequate supply of food in close proximity to
