The swift seldom visits us before the beginning of May, nor remains later than the middle of August.
In the height of summer these very active birds are on the wing at least sixteen hours in the day, withdrawing to rest, in the longest days, about a quarter before nine o'clock in the evening, some time after all the other diur nal birds have retired. Just before they repair to their re spective holes, they assemble in large groups, high in the air, screaming and shooting about with wonderful activity ; but they are never so alert as in sultry lowering weather, when they manifest great alacrity. Their sight is parti cularly acute; and, according to the experiments of Spal lanzani, they can distinctly perceive an object of five lines in diameter, at the distance of 304 feet. They generally build their nests in elevated places, such as lofty steeples and high towers, but sometimes under the eaves of roofs or the arches of bridges, and even in hollow trees, com posing it of a variety of materials, as dry grass, moss, hemp, bits of cord, threads of silk or linen, small shreds of gauze or muslin, feathers, the down of poplars, and other light matters, which they frequently catch in the air, or snatch up as they skim over the surface of waters, or detach from trees, or of which they rob the sparrow and other small birds. Unless much molested, they return to the same breeding haunts, which seem to be transmitted from one generation to another. If they find their nest occupied by the sparrow, they compel the latter to resign its pretensions; nor are they in the least scrupulous of seizing on the legitimate nest of that bird, and adapting it to their purpose, lining the materials of the joint fabric with a yield humour, which is constantly present in their throats and in their bill, and which enables them to entan gle the insects which they seize. This substance, by pe netrating the nest in every direction, imparts to it consis tency and even elasticity. The female has only one brood in the season, and lays from two to five eggs, which are of a very lengthened and pointed form, white, larger than those of the swallow, and having a very brittle shell. The
female alone performs the duty of incubation, rushing forth just before dark, to relieve her weary limbs, snatch a scanty meal for a few minutes, and then return to her charge. It should seem, however, that the male hovers about in the neighbourhood, and occasionally fetches her food, uttering his scream as he wheels ahout the nest. The young have a feeble cry, are fed by both parents five, or even six times in the course or the day ; and their food, which they swallow entire, consists of insects, such as winged ants, flies, beetles, butterflies, spiders, &e. In the course of four or five weeks they quit the nest, and, con trary to the habits of some of their kindred tribe, do not return to it for a resting-place. They generally fly and feed high in the air, and range to great distances : they may sometimes, however, be observed hawking very low, and for hours together, over pools and streams, in search of phryganex, ephemera, and libellulx, which frequent the banks and surface of waters, and which afford them a plentiful and succulent nourishment. They sometimes pursue and strike at birds of prey, but with less vehe mence and fury than the swallows. Like the latter, they sip up water as they skim along its surface. During the middle of a very hot day, they are seldom seen out of their holes ; but in the morning and evening they may be ob served in troops, more or less numerous, sometimes de scribing a thousand circles in the air, sometimes defiling along a street, or wheeling round a large edifice, whilst at other times they sail along, without any perceptible mo tion of their wings, and then suddenly and frequently agi tate them, as if impelled by some precipitate instinct. Previous to their departure, they begin to assemble early in July, when their numbers daily increase, and large bo dies of them appear together. They then soar higher in the air, utter shriller cries, and fly in a peculiar style. These meetings continue till they finally disappear.