The city built by the rooks in the elms of the great pasture field (the Warren, near Wick farmhouse) is divided into two main parts; the trees standing in two rows, separated by several hundred yards of sward. But the inhabitants appear to be all more or less related, for they travel amicably in the same flock and pay the usual visit to the trees at the same hour. Some scattered elms form a line of communication between the chief quarters, and each has one or more nests in it. Besides these, the oaks in the hedgerows surrounding the field support a few nests, grouped three or four, in close neighbourhood. In some trees near the distant ash copse there are more nests whose owners probably sprang from the same stock, but were exiled, or migrated, and do not hold much communion with the capital. In early days men seem to have frequently dug their entrenchments or planted their stockades on the summit of hills. To the rooks their trees are their hills, giving security from enemies. The wooden houses in the two main streets are evidently of greater antiquity than those erected in the outlying settlements. The latter are not large or thick: they are clearly the work of one, or at most two, seasons only; for it is noticeable that when rooks build at a distance from the centre of population they are some time before they finally decide on a site, abandoning one place after another. But the nests forming the principal streets are piled up to a considerable height--fresh twigs being added every year--and are also thick and bulky. The weight of the whole must be a heavy burden to the trees. Much skill is shown in the selection of the branches upon which the foundations are laid. In the first place, the branch must fork sufficiently to hold the bottom twigs firmly and to give some side-support. Then it must be a branch more or less vertical, or it would swing with the wind too much up and down as well as to and fro. Thirdly, there should be a clear or nearly clear space above the nest to give easy access, and to afford room for it to increase in size annually. For this reason, perhaps, nests are generally placed near the top or outer sides of the tree, where the boughs are smaller, and every upward extension reaches a clearer place. Fourthly, the bough ought not to be too stiff and firm; it should yield a little, and sway easily, though only in a small degree, to the breeze. If too stiff, in strong gales the nest runs the risk of being blown clean out of the tree. Fifthly, no other branch must rub against the one bearing the principal weight of the nest, for that would loosen the twigs in time, and dislocate the entire structure. Finally, rooks like an adjacent bough on which the bird, not actually engaged in incubation can perch and `caw' to his mate, and which is also useful to alight on when bringing food for the young.