National Geographic : 1932 Jul
THE NATIONAL GEOGRAPHIC MAGAZINE Photograph by Dr. Frank N. Wilson A NIGHTHAWK EXAMINES TIER NEST AND EGGS: BEAVER ISLAND, LAKE MICHIGAN the viscous saliva of the bird to form a basket that is fastened by this, same saliva to the inside of hollow trees or chimneys, to the branches or leaves of trees, or to the walls of cliffs or caves. The eggs are pure white and range in number from one to six, according to the species. The swiftlets (genus Collocalia), small est in their family, have most peculiar nest ing habits. It is this group that produces the edible birds' nests prized among the Chinese for making soup. The edible nests are made principally by two species which frequent caves, in col onies containing thousands of individuals. The nests are composed of a mucous secre tion from large glands opening into the mouths of the birds. This substance is molded against the rock to form a small platform, with a hollow in the top to re ceive the two eggs. The better-grade nests, which are com posed entirely of the glandular secretion and are nearly white, are gathered by na tives and sold for food. The second nests made are reported to be mixed with vari ous vegetable substances, as the secretion from the bird itself seems insufficient. When these second nests are taken the bird forms a third structure, that is composed of various substances cemented together with a little saliva. The caves where these birds nest are visited annually by natives, who take the first and second nests, leaving the third one for the birds to use in rearing their fami lies. When the young are on the wing, this final nest is destroyed to insure that a new one of good quality will be constructed at the next breeding season. The food of swifts, so far as known, consists entirely of insects captured on the wing. In the Tropics swifts consume ter mites or white ants during their periods of flight. While these birds have short bills, the gape is wide, forming a scoop in which food is seized. The notes of swifts are chattering, squeaky calls with little musical merit. THE GOATSUCKERS The order of goatsuckers, found throughout the temperate and tropical parts of the earth, includes four families: the frogmouths (Podargidae), the wood nightjars, or potoos (Nyctibiidae), the owlet frogmouths (Aegothelidae), and the true goatsuckers (Caprimulgidae).