BRITISH WARBLERS
But with respect to this law of territory we must still regard a community as one unit, for community rights with community as one individual rights with another. The Books from one rookery will attack those from another, the members of one colony of Gannets (Sula bassana) will struggle with those of another. And it is possible that the attainment of reproduction may be an even more difficult task for those species that are sociable, since battles occur between individuals with respect to their own particular domain even within the precincts of the territory of a community. At no time are the Books so quarrelsome as when they commence to build their nests, and though the quarrel may be only caused by one stealing nesting material from another, yet they certainly appear to respect one another's rights. But even the stealing of twigs and wool would be similar in its results to a battle, if thereby any particular individual were prevented from breeding. Circumstances compel other species to breed together. For many sea-birds breeding stations are few and far between; nevertheless, even the members of these cliff-breeding species seem to have their own particular territory; and it must be remembered that not every Gull nor every Guillemot on a ledge of rock is a breeding bird. The working of the law of territory is a beautiful illustration of adaptation, since a territory is developed in some instances to ensure an ample supply of food for the helpless young, while in others it is gradually limited in extent to ensure reproduction, but in every case perfected so as to hamper in no way, but rather improve the position of the species in relation to the struggle for existence. Thus scarcity of breeding stations, scarcity or abundance of certain types of food, and the relation between the supply of food and the localities suitable for breeding purposes must have been taken into consideration as species arose and adjustments were made accordingly. If the individuals of any one species were to develop a territory larger than was necessary, and by so doing prevent a portion of their own community from breeding, that species would gradually
30
