Swifts do not willingly alight on the ground, even to collect materials for their nests, nor do they perch on trees or roofs, the arrangement of their toes being quite unsuitable for either action, and the length of the wings being such that, even with toes of the normal type, walking would be almost impossible. The nest, a somewhat rude structure of grass and feathers, is generally built in high towers or other tall buildings. The eggs are two in number; they are more conical in shape than those of the swallow, and, as the position of the nest renders them independent of protective colouration, are white. The hen-bird sits on them during the day, but generally leaves the nest and flies abroad in the evening to hunt for insects. Only one brood is reared, and the birds take their departure early in August, to spend the winter in South Africa or Madagascar. [Pg 324] The cuckoo.—The cuckoo is placed by naturalists, not among the passerine birds, but in the order to which the swift belongs. The reasons for this cannot be fully considered here, but it may be mentioned that the cuckoo has only 10 tail-feathers, and that it differs from all passerine birds in having its fourth toe, as well as the first, directed backwards, the second and third pointing forwards (Fig. 210). The cuckoo has a total length of about 14 inches. The upper surface of the body, and the throat, are grey; the rest of the lower surface is white, crossed with black bars. The wings are large and powerful, and the thighs are covered with long feathers. In general appearance, as well as in manner of flight, the cuckoo bears a great resemblance to a hawk, which may perhaps be the reason why small birds so often join forces and attack it. A keen-eyed observer will, however, at once distinguish the birds by the head and the bill, both of which are markedly longer in the cuckoo than in the hawk. Cuckoos arrive here in April, the males usually appearing first. The well-known call, to which the bird owes its name, is uttered by the male only; the voice of the female is quite different, and is often compared to the sound of bubbling water. The cuckoo feeds entirely upon insects; it is believed to be the only bird which eats the hairy caterpillar of the tiger-moth (p. 369). Fig. 210.—The Cuckoo, (× ¹ ₇.)