It may be that the difficulty of finding trees which afford all these necessary conditions is one reason why rooks who settle at a distance from their city seem long before they can please themselves. The ingenuity exercised in the selection of the bough and in the placing of the twigs is certainly very remarkable. When the wind blows furiously you may see the nest moving gently, riding on the swaying boughs, while one of the birds perches on a branch close by, and goes up and down like a boat on the waves. Except by the concussion of branches beating hard against the nest, it is rarely broken; up to a certain point it would seem as if the older nests are the firmest, perhaps because of their weight. Sometimes one which has been blown down in the winter--when the absence of protecting leaves gives the wind more power on them--retains its general form even after striking against branches in its descent and after collision with the earth. Elms are their favourite trees for building in. Oak and ash are also used, but where there are sufficient elms they seem generally preferred. These trees, as a rule, grow higher than any others ordinarily found in the fields, and are more frequently seen in groups, rows, or avenues, thus giving the rook facilities for placing a number of nests in close neighbourhood. The height of the elm affords greater safety, and the branches are perhaps better suited for their purpose. After building in an elm for many years--perhaps ever since the owner can remember--rooks will suddenly desert it. There are the old nests still; but no effort is made to repair them, and no new ones are made. The winds and storms presently loosen the framework, about which no care is now taken, and portions are blown down. Then by-and-by the discovery is made that the tree is rapidly dying. The leaves do not appear, or if they do they wither and turn yellow before Midsummer: gradually the branches decay and fall of their own weight or before the wind. No doubt if anyone had carefully examined the tree he would have observed signs of decay long before the rooks abandoned it; but those who pass the same trees day after day for years do not observe minute changes, or, if they do, as nature is slow in her movements, get so accustomed to the sight of the fungi about the base, and the opening in the bark where the decomposing touchwood shows, as to think that it will always be so. At last the rooks desert it, and then the truth is apparent.