The house martin (_urbica_), or window swallow or martlet, is smaller and less agile than its cousin just described, and has a far shorter tail. Its feet and toes are downy. It comes later than the chimney swallow, builds amidst towns, on the _outside_ of houses, under eaves and in window niches, and chooses a northern aspect to avoid the direct rays of the sun, which would crack its mud nest. Martlets sometimes build on the face of cliffs, as may be seen at the Giant’s Causeway. It has four or five _white_ eggs, and brings out two broods. As a vocalist it can only get as far as a chirp, or at most a small twitter. Its body is white below, and purple on the back and wings. The house martin does not, like the chimney swallow, sweep the ground and water in its flight. The bank swallow (_riparian_) or sand martin, which is so sociable with its own kind but not with man, digs horizontal and serpentine holes in banks, sloping upwards to avoid rain, where it lays in a careless nest four or six white eggs. It has sometimes, but perhaps not always, two broods. These are the smallest and wildest of our swallows; nearly mute, or with only a tiny chirp; and, when they can, frequent large spaces of water. They often fly waveringly with a quick fluttering of wings, somewhat like butterflies, and anon sail circling like other swallows. They use their old caves for some years, but may often be seen digging new ones. They are probably driven out sometimes by the fleas which, as I have often seen, abound in their habitations. Birds, indeed, free and airy as their life seems, suffer much from vermin, and the poor baby swallows are terribly preyed upon. The sand martin is mouse-coloured on the back and brownish-white below. It is the earliest to arrive in England, and may be expected now in three weeks or so. Next we may look for the chimney swallow with his long tail—then for the house martin, and latest of all comes the swift (_Cypselus_), which some naturalists say is no true swallow, having several anatomical peculiarities, the most noticeable being that all four toes go forward. No other bird, I think (save the Gibraltar swift), has a similar foot. The swift can cling well to the face of a wall, but cannot perch in the usual bird fashion, and gets on very badly on the ground, finding it difficult to rise on the wing. Once in the air, with its long wings in motion, it is truly master of the situation. It is one of the speediest, if not the speediest, and can keep on the wing for sixteen hours, which is longer than any other bird. The swifts are most active in sultry thundery weather. They fly in rain, but dislike wind. They are the latest day-birds in summer, and their one very shrill note may be heard up to nearly nine o’clock. Sometimes they get excited and dart about screaming, perhaps quarrelling, but usually the swallows, all of them, agree well among themselves, though they also keep a proper distance.