The coloration is usually greenish-black or mouse-brown, occasionally with a white chin, breast, or rump; a rufous collar or chestnut ear-coverts occur in Macropteryx and Cypseloïdes, where alone the males differ from the females, and the young from both. The Family ranges over the whole world, with the exception of the extreme north and south, New Zealand and some other islands; the six genera containing about eighty species varying in size from about four to fourteen inches.
Swifts are essentially aërial, seldom alighting upon the ground, or perching except at night,[[241]] though they will cling to the entrance of their breeding quarters for a few seconds before entering. From a smooth flat surface they can hardly rise, but in the air they are perfectly at home, whether wheeling and circling at great altitudes, chasing each other aloft, consummating their love affairs, or sweeping over the earth's surface in pursuit of insects attracted by the damp. The exceptionally rapid flight is strong and practically unlimited in duration, two or three quick movements of the wings being repeatedly succeeded by a gliding motion. Though not gregarious in the ordinary sense, they habitually breed in company, and Collocalia nests in vast colonies; a solitary bird, moreover, is comparatively seldom seen, and both before and during incubation our Common Swift flies in screaming flocks around the chosen sites. This species will pass and re-pass close to a pedestrian's head with noisy and apparently vicious rush, even when far from the nest; yet it is not really the intruder but insects that are the attraction, the food being entirely of that nature, and invariably captured in the air, while the beak may be seen filled to repletion when nestlings require to be supported. The voice is a shrill scream, constantly repeated. The districts frequented are of every description, Cypselus andicola and C. horus being particularly alpine; the nest varies to a considerable extent, though a glutinous substance secreted by the highly developed salivary glands is a constant, or frequently almost the sole, material. The situation may be a hole under thatch, slates or tiles; a crevice in a building, cliff, or tree; the perpendicular wall of a cave; the upper side of a branch, palm-leaf, or broad stalk; the lower surface of a rock, and so forth. The shape of the structure is tubular in Panyptila, where it is composed of seeds of plants; but generally it is saucer-like, the materials being straw, feathers, twigs, moss, or cottony vegetable matter, the first two of which have been stated to be caught floating in the air. The American Chimney-Swift plucks off branchlets as it flies. Cypselus affinis and the species of Collocalia commonly join their nests together in masses; Palm Swifts do so more rarely; Cypselus caffer even utilizes those of other birds. The dull white eggs are oval and almost uniform at each end; two or four being the usual complement, though three are exceptionally found, and Macropteryx lays only one.
Sub-fam. 1. Macropteryginae.–The Tree-Swifts, as they are called, have very soft plumage, a long, deeply-forked tail, a patch of downy feathers on the flanks, and elongated plumage on the top or sides of the head. They range from India and Ceylon through the Burmese and Malay countries, and the islands thence to the Solomon Group. Macropteryx coronata of India, Ceylon, Burma, and Siam has bluish ash-coloured upper parts, glossed with metallic green, especially on the crested head, wings, and tail; the under surface is greyish and white, the chin and ear-coverts are rufous. The female lacks the chestnut. The nest is a half saucer of bits of bark and feathers, gummed by saliva to a branch some twenty feet from the ground, trees being usually selected in rough jungle on low hills. It contains one egg, and is so small that the sitting bird quite conceals it. Other species are M. longipennis, M. wallacii, M. comata, and the larger and most eastern M. mystacea.
Sub-fam. 2. Chaeturinae.–Of the three genera, Chaetura, Cypseloïdes, and Collocalia, the first occurs from Central Asia and India to Japan, New Guinea and Australia; in Tropical Africa; and in the Nearctic and Neotropical Regions, except the extreme north and south. All the species, numbering about fifty, have rigid tail-feathers with more or less projecting spiny shafts, save in Collocalia.
Chaetura caudacuta, which has strayed to Britain and New Zealand, ranges from Mongolia and Japan to China and the Eastern Himalayas, wintering southwards to Australia and Tasmania. It is dusky-brown with greenish-black head, wings, and tail, white forehead and breast. The nest, placed on cliffs or in hollow trees, is probably similar to that of the next species, several pairs nidificating together. C. pelagica, the "Chimney Swallow" of the United States, chiefly found in the east, but extending to the Fur Countries and the Great Plains, and in winter at least to Mexico and Yucatan, is dark grey, with lighter lower surface, blackish head and wings. It has almost ceased to breed in trees, but fastens its semicircular nest of small twigs, glued together with salivary secretion, to the inside of chimneys, laying from four to six white eggs. C. zonaris, extending from the West Indies and Mexico to Argentina, is uniform blackish-brown with white collar and breast; C. novae guineae of Papua is glossy greenish-blue above, and grey below, with an exceptionally short tail; C. ussheri of the Gold Coast is dark brown, varied with a good deal of white; C. cassini of the Congo and Gaboon, and C. boehmi of East Equatorial Africa, are glossy black with less white. C. acuta of the West Indies, C. grandidieri of Madagascar, and other forms, complete the genus.
In Cypseloïdes the shafts of the rectrices scarcely project perceptibly; while the tail is emarginate in C. niger of western North America, the Antilles, and Guiana. The coloration is plain black or brown, with a reddish collar round the neck in the males of C. rutilus and C. brunneitorques. The genus ranges to Peru and Brazil. The nest, placed in holes in houses and so forth, is made of straw, leaves, and rubbish; the eggs are four or five.
Collocalia is an especially interesting section of the Family, on account of the nests furnishing the birds'-nest soup of the Chinese. Being formed of the dried secretions of the salivary glands,[[242]] these are almost entirely glutinous, and when newly built are termed white or "first quality." The thirteen diminutive species are black or brown above, occasionally with a blue gloss, and white on the rump or tail; the under parts being whitish or grey. They are not migratory, but extend over most of the Indian and Australian regions, except the northernmost portions, being found as far south as North Australia. One form reaches the Mascarene Islands. Huge numbers breed in company in dark caves, sticking their nests close together upon the rocky walls, or even joining them in masses; the materials may include moss, straw, lichen, and so forth, but inspissated saliva is the chief, and often the only, constituent, especially in C. fuciphaga. Brown nests are those discoloured by use, or spoilt by an admixture of foreign substances, and are considered hardly worth collecting. Two eggs are the usual complement. The caverns are entered from boats below, or by ladders from above, other ladders or poles notched for the feet being fixed in the rocky flooring of the interior. These are ascended by natives armed with long-pronged forks, who obtain hundreds of nests at one gathering. Bats occupy the caves by day, the birds by night or when incubating; while at any time the noise of the escaping denizens is almost deafening. The breeding sites are a very lucrative property. The especially valuable C. fuciphaga, which obtained its specific name from the erroneous idea that it built with partly digested sea-weed, extends (if we include several more or less distinct races) from the Duke of York Island and the Ladrones in the east to the hills of India, Ceylon, and the Mascarene Group in the west, a small species of slightly more eastern range with whitish band on the rump being known as C. francica.
Sub-fam. 3. Cypselinae.–This contains only the genera Panyptila and Cypselus, granted that the latter is not further divided. The former has feathered toes, a deeply forked tail with pointed outer feathers, and soft, silky black plumage, varied with white. The very remarkable architecture of P. sancti hieronymi of Guatemala is described as follows by Mr. Salvin:[[243]] "The nest of this species is composed entirely of the seeds of a plant, secured together and hung from the under surface of an overhanging rock by the saliva of the bird. The whole structure measures 2 feet 2 inches in length, and is about 6 inches in diameter. The entrance is at the [lower] end, and the hollow for the eggs at the top." The cavity in the above case was in the shape of a walking-stick, with its knob bent laterally at the top, while a false entrance shewed at one side. P. cayennensis, ranging from Nicaragua to Brazil, makes a similar nest on trees.
The coloration of the twenty or more species of Cypselus is sooty-black or mouse-brown, frequently exhibiting a metallic gloss, while the collar, rump, abdomen, or edges of the feathers may be white. A forked tail is not uncommon, and the strong toes are feathered in C. melanoleucus and C. squamatus. C. apus, the Common Swift or Deviling of Britain, is found through Europe, North Africa, and Asia southward to the Himalayas, migrating to South Africa, Madagascar, and Southern Asia. A paler race (C. pallidus or murinus) extends from the Atlantic Islands and the Mediterranean basin to Bogos Land and Sind. The habits are well-known; but it may be observed that in flying the wings take the form of a bent bow, and that on the Continent it builds in hollow trees instead of in holes under eaves, in walls or cliffs. Few individuals remain with us after early September. C. unicolor is peculiar to Madeira, the Canaries, and the Cape Verd Islands; C. affinis reaches from Africa and Palestine to India; C. melba, the "Alpine Swift," inhabits the same Asiatic countries, extending westward to South Europe and North Africa, and wandering north to Britain and Heligoland.
