The principal species we have already named. It is only necessary to mention the Cliff Swallow ([Fig. 241]), the Chimney Martin, the Bank Martin, and the Alpine Swift (Cypselus alpinus), [Fig. 242].
Fig. 242.—The Alpine Swift (Cypselus melba, Wood).
Among the foreign species the Salangane Swallow ([Fig. 243]) may be mentioned, so famous over the world for its edible nest. This bird inhabits the rocks and caverns of the sea-shore in Sumatra and Java. When building it eats of the plant called fucus, which abounds in these regions; this is metamorphosed in the bird's stomach, and afterwards disgorged, to fabricate the walls of its nest. The fucus thus devoured forms the nutritive substance so eagerly sought after by the Eastern gourmet. The consumption of the nest of the Salangane ([Fig. 244]) in China, in spite of its high price, is very considerable. From the days of Buffon there have been exported from the coast of Cochin China four millions of them annually; and the proprietors of one cavern in the island of Java receive annually fifty thousand florins for rent alone.
Fig. 243.—The Salangane Swallow (Hirundo esculenta, White).
The distinctive features of the Goatsuckers (Caprimulgus) are a short, much-depressed bill; the body small in proportion to the plumage; the neck short; the head large, broad, and depressed; the eyes very large and broad; the feet very small; tarsi partially feathered; toes four, the lower surface broad and flattened, the anterior toes connected by basal membranes; claws moderate, arched, and compressed. The plumage is full, soft, downy, and blended, like the Owl's; the wings have the second and third quills longest; tail long and rounded. Almost all the species have strong bristles along the base of the upper mandible, and some have the feathers of the face radiated, like those of the Owls.
Fig. 244.—Nest of the Salangane Swallow.
The Goatsuckers are solitary birds, living generally in pairs, sleeping during the day, and issuing from their nest with the setting sun, or possibly earlier in gloomy weather, to chase the crepuscular and nocturnal insects on which they feed. They move silently and with great rapidity. Some authors say that when on the wing they keep the mouth open; but this is not supported by facts, and is opposed to reason. The insects they principally devour are moths, dragon-flies, beetles, crickets, cockchafers, and mosquitoes. Their usefulness, therefore, is nearly equal to that of the Swallow. As they get very plump and fat in the autumn, they fall a sacrifice to the gunner, and in their turn are eaten by gourmets greater than themselves. They are migratory birds, travelling only during the night. They are readily distinguished by the bristles at the base of the bill, and by the claws of the middle toe, which is toothed. The object of this toothed appendage has been the subject of speculation. Some writers fond of the marvellous even surmise that it is intended to comb and smooth the head feathers. Mr. Vigors is of opinion that it may be useful as a further power of prehension, citing, in support of his view, the family of the Ardeidæ among the Wading birds, which exhibit an analogous construction in the middle nail.