BIRDS. The nest-making of birds is most familiar and perfect, yet it is only among the higher forms that it is manifested to any great extent. In no respect is there greater diversity among birds than in the structure of the nest. As a rule, its character is closely associated with the intelligence of the bird. modified more or less by the necessities of the situation and the structure of the bird's bill and feet. The nests of ostriches and other Ratite are mere accumulations of sand or earth, or cavities scraped in the ground. The nests of the lowest water-birds consist of burrows in the ground. or the eggs are laid on the bare earth or rock. (good examples are the guillemots (q.v.). The king-penguin treats its eggs in the same way. those a little higher in the scale. nests of sea-weed and coarse grass lotisely put together make a home for the young. Most of the ducks and geese build nests of grass. and often in clude feathers from their bodies. a habit carried to the extreme in the cider-duck (q.v.). Few of the wading birds build nest, the coming nearest to it with a platform of sticks. The grouse and quail, turkey and pheasant, all Scrape together nests of leaves and grass on the ground. The allied mound-birds are remarkable for collecting great heaps of decaying vegetable matter, ill which the eggs are laid. the heat caused by the decay ripening them. Doves and pigeons usually build a very trail nest of twigs. but a few species are ground breeders. Eagles, hawks, and vultures construct coarse, heavy nests of sticks and twigs on large trees or cliffs, while owls often resort to hollows in trees, or to the deserted burrow of some mam mal, especially the prairie dog. Parrots, wood peckers, kingfishers. mouse-birds, todies, and some others lay their eggs in holes in trees, or in earthen banks, with little or no bedding. Humming-birds (q.v.) build the most delicate and beautiful nuts known; and swifts extraor dinary ones, consisting largely of mucilaginous saliva. (See CIIININEY•SWIFT; SALANGANE.) Many song-birds build on the ground, where the nest is more or less cleverly concealed, but the great majority build in trees or bushes. The most remarkable nests built by any birds are those of the American orioles or hangnests, and more especially of the weaver-birds (q.v.) of Africa and the East Indies.
The perfection of many nests for the purposes to which they are put, and the ingenuity, skill, and apparently :esthetie sentiment displayed by many birds, long ago led to some study and much speculation. An excellent book was made
upon the subject early in the nineteenth een tury—Rennie's Architecture of Birds (London, 18311. Ile divided his subjects into such classes as ground-nesters, squatters, and miners; build ers of mounds, of umbrellas. of domes; masons; carpenters ; plat form-makers : basket Aim kers ; weavers; tailors; fellers; and cementers. This was purely artificial. but did well enough so long as nests and eggs were treated as things separate from the bird itself. About forty years later Wallace included in his book Contributions to Selection (London, ISTO) an essay on "A Theory of Birds' Nests," in which he discussed the subject from an evolutionary point of view, showing the analogy between the method of birds and primitive men in meeting their diverse requirements of shelter out of the ma terials most available. Wallace places birds' nests in two great elasses—a functional. not a structural, classification. The first class includes those in which the eggs, young, and brooding parents are not exposed. To this group belong nests that are built in natural covers, such as boles in trees or in banks and Hid's, as well as nests covered by the bird, such as the susl.ended nest of the American orioles. To the second class belong the nests of the ordinary type, cup. shaped and open above, so that the eggs, young. and brooding females are exposed. This contrast in method of nidification, as lie believed. cor related with the color of the female. As lie says: "When both sexes are of strikingly gay and conspicuous colors the nest is of the first class. or such as to conceal the sitting birds; while. whenever the male is gay and conspicuous, and the nest is open sit as to expose the sitting bird to view, the female bird is of dull or obscure colors." The comments and criticisms upon this theory by the Duke of Argyle. by Prof. A. Mur ray, and by A, Allen (Bulletin NOW! Ornith, Club, vol. iii., Cambridge. 18781, and by others more recently. show that it is not so universal in its application or full• explanatory as its author considered it. The hypothesis was re stated, with improvements, by Wallace, in Dar winism (New York reprint. 1889).