and destroyed the eggs, with the result that not a single pair of Rooks was left in the settlement. Each Rook must therefore secure a position within the precincts of the community if it is to have a chance of success in the attainment of reproduction. But every locality cannot supply sufficient trees of the right kind, appropriately situated and in suitable relation to the food supply, in which numbers of nests can be built in close proximity; so that if more than one community were to attempt to establish itself in a limited area, the supply of food or the supply of trees might become a pressing problem. Each community must therefore be prepared to defend its own interests, and each must be regarded as one unit and the area occupied as one territory within which are included a number of lesser territories. The individual may fail to establish itself within a community, but, even if it succeeds, the community may fail to establish the rights of communal ownership; hence it has to face a twofold possibility of failure, and if it lacked the inherited nature which leads the Guillemot to secure a position upon the ledge, or the Bunting to obtain a position in the marsh, the chances are that it would fail in the attainment of reproduction.
The question now arises as to how it comes about that the area occupied by each individual conforms in broad outline to that which has proved beneficial for the welfare of the species as a whole. We shall find that up to a point the answer is a simple one. No one could study
