The Encyclopedia Americana (1920)/Birds, Nests of
BIRDS, Nests of. The receptacles prepared by birds for the holding and security of their eggs and young. The eggs of birds are few in number, larger in proportion and more advanced in development than those of fishes, amphibians or reptiles, and are encased in fragile shells, the rupture of which would be fatal to the enclosed embryo; they are never (with a single exception) buried out of harm's way; and they require a comparatively high degree of warmth, continuously applied, in order to mature successfully into living and energetic young. (See Egg). To meet these complicated conditions of success great care is necessary on the part of the parent-birds; and the necessity for this care increases in proportion to the superiority of organization and development of the bird, — a matter of wide range in the class. The young of the higher forms, as hawks and thrushes, would inevitably perish under the limited care that suffices for such lower forms as the seafowl. In this view birds are divisible into two classes: first, those whose young are developed within the egg, that is before hatching, to such a point that they are able as soon as freed from the shell to run about, pick up their food and to a great degree take care of themselves; second, those hatched before they have reached this state of advancement, and which hence must he fed, protected and guarded by their parents until they have completed their development to the point of self-care. Parental preparations for the former need have regard only to the proper incubation of the eggs; for the latter it must be extended to the safety and comfort of the young for a period after they have hatched, greater or less according to their helplessness, which varies with the degree of organization. It is among birds of the highest organization, therefore, that complete and elaborate nests are alone to be found, because there only are they required as cradles and homes for the young.
The seafowl, such as penguins and auks, make no nest whatever, depositing only a single egg on some cliff-ledge or sea-islet, almost inaccessible to enemies, and covering it with their warm bodies until the young one hatches, when it is immediately ready to go into the water and fish for itself. The great company of shore-breeding birds, gulls, sandpipers, etc., need do nothing more than scrape a smooth hollow among the pebbles or sea-wrack where their eggs may lie close together and not roll or be blown away. The waterfowl — rails, ducks, pelicans and other, — seeking the greater seclusion of marshes and swamps, must do a little better, making a firm raised bed of earth with a rim around it, or else a platform of reeds, etc., to keep their eggs out of the mud or water. Some of these, as the herons, cormorants and the like, have learned to make their homes in bushes and trees, and these are likely to be rather more substantial than those on the ground, to prevent their falling to pieces in the swaying of the branches, or dropping the eggs over the side or through the bottom. Similarly the great tribe of ratite, limicoline and game-birds, which breed inland on the ground, do not make nests in such sense as are those of the song-birds, but mere beds for the eggs, since these are all Precoces, or Nidifugæ, that is, of those whose chicks run about as soon as they hatch.
The higher families of birds, however, called Altrices or Nidicolæ (but more convenient terms for these classes are found in the words “independent” and “dependent,” respectively), must safeguard and nourish their young for a period after birth from the egg, and these must make a home for them which shall be durable and of such a form and finish as shall protect the helpless young from bad weather, observation and attack, and prevent their falling out. These objects are attained with a varying degree of success, but in many cases seem to be almost perfectly accomplished, and the nests resulting have added to them the finish of great beauty. Some birds' nests are marvels of skill, ingenuity and adornment; while others, perhaps made by nearly related species, are rude or slovenly.
Classifying Nests.— Several of the earlier writers on ornithology have attempted to classify birds according to their modes of nest-building. Such attempts are not without value, but they are purely artificial and of no use to the systematic ornithologist. The classification of nests may take account of their situation, means of support, shape, materials or other characters, or of two or more of these. Taking the first-mentioned consideration as a basis we may group birds into miners, such as the kingfisher and the sand-martin; mound-builders, like the brush-turkey and scrub-pheasant of Australia; masons, which use a sort of mortar of earth or clay, including several swallows and allied birds, etc. One of the most distinctive categories is that of the borers, such as the woodpeckers and their relatives, which carve out tunnels and chambers in the trunks of trees as breeding-places. Many of the terms employed in nest classification are useful for descriptive purposes. Such are platform-nests, basket-nests, pensile nests, etc., or, as names of birds, weavers, tailors, felt-makers, etc. As a general rule birds of the same family or lesser group will agree pretty well in their style of nidification; but there are many exceptions, as, for example, the North American tyrant-flycatchers, among which a remarkable diversity of style in architecture exists.
Methods of Construction.— Birds choose for their nests the material of that kind to which they are habituated which lies nearest; and if it cannot be found will seek a good substitute, so that the nests of birds whose specific ranee covers a wide region will be found varied greatly and often much improved in some localities. Similarly the builders are likely to change the site when necessary, breeding in trees in wooded regions and on the ground or rocks where trees are absent. In this way certain birds have greatly modified their nesting habits since the civilization of their habitats — notably the swallows and swifts which all over the world abandon, as a rule, their natural breeding places in hollow trees, or about rocky cliffs, and make their nests under the roofs of farm outbuildings or in bird-boxes. The nests of closely related birds may vary considerably. In many, families, as, notably, in the Fringillidæ, some species nest on the ground, others in bushes or trees; and it is hard to say which is to be considered the normal method.
A bird's nest sometimes forms an immense mass, as is the case with the birds of prey, crows, or herons, one of which, the umbrette of central Africa, makes a home large enough to fill a dumping-cart. Such great structures are likely to be used many years in succession; but few small nests outlast the winter. The hollow bed in the centre is formed by a lining of lesser and smoother substances. Small birds naturally use finer materials, and the character of the structures varies with the characteristics and habits of the birds. Some are made almost wholly of twigs, others of grass blades, others of flexible ribbons of such bark as that of the grape-vine, others of shreds of hempen fibre torn from the milk-weed and similar plants, others of a matted felt formed of the down of cat-tail flags or of ferns. Some are made in whole or in part of mud, and plastered upon rocks, either supported upon a ledge or projecting glued to the face of a cliff like a hollow bracket. Of this shape are the nests of many swifts, some of which are composed almost wholly of glutinous saliva, as is the case with that of the edible swift mentioned below. Some of the rudest nests externally are beautifully soft and smooth within; while others are exquisitely finished and adorned outside as well as in; or are intricately woven, as are the pensile hammocks of the vireos, the pouches of the Baltimore orioles, European titmice and others. and the leaf-sewn nests of the tailor-birds and many humming-birds. In most cases the female is the architect, while the male is permitted to do little but bring materials which are often rejected by the fastidious builder. While most, especially of the smaller kinds of birds, separate into pairs and seek secluded places for their homes, others breed gregariously, as is the custom of many seafowl and most herons, pelicans, etc. Some of the land-birds, as the swallows, betray a tendency toward this; but the most remarkable case is that of the African social weaver-birds (q.v.), which actually build a roof in common, beneath which each pair of the flock establishes its individual dwelling. This strictly community life does not occur elsewhere among birds, although cases of commensalism are occasional.
Edible Nests.— Few birds' nests serve any human utility, though many are utilized by other members of the animal kingdom. One, however, is valuable as food. This is the nest of the selangane (Collocalia fuciphaga) or of related species of swift or swiftlet of the Malay Archipelago, used as a delicacy by the Chinese. It has the shape and size of a half teacup, is attached to the rock in the interior of a cave and has the appearance of fibrous gelatine or isinglass. It is composed of a mucilaginous substance secreted by special glands, and is not as was formerly thought made from a glutinous seaweed. The caves in which these swifts dwell in crowds are numerous in northern Sumatra and in Borneo, especially near the north end of the island, and are in most cases the property of wealthy owners, who get a large annual income from the hazardous occupation of securing the nests, which can be done only by climbing about the interior of the great sea-caves, holding torches and raking off the nests into little bags hung upon the end of the pike-poles. The best, which are whitish in color, and almost free from any mixture with the pure glutine from the glands in the mouth of the bird, are worth $10 to $15 a pound.
Among works dealing with the subject of birds' nests are Rennie, ‘Architecture of Birds’ (London 1831); Wood, ‘Homes Without Hands’ (New York 1865); Pycraft, ‘Infancy of Animals’ (New York 1913). Special books for the United Slates and Canada are Bendire, ‘Life Histories of North American Birds’ (with colored plates of eggs, Washington 1892-95); Davie, ‘Nests and Eggs of North American Birds’ (Columbus, Ohio 1898); Reed, ‘North American Birds' Eggs’ (New York 1904); Ingersoll, ‘Primer of Bird Study’ (New York 1915).