The New International Encyclopædia/Nidification

NIDIFICATION (from Lat. nidificare, to make a nest, from nidus, nest + facere, to make). Strictly, the act and process of nest-building. In the present article, however, the word will be broadly interpreted, so as to include the entire series of acts, instincts, and adaptations connected with the provision of a temporary breeding-home, nidus, or ‘nest’ for their eggs, embryos, or young, and the care of offspring, by the parents of animals generally.

A nest differs from an animal's ordinary residence in that it is not made primarily for the animal's own use, but for that of expected young. In some instances it is mainly a convenient lying-in place for the mother; in others, merely a means for the safety and comfort of eggs or helpless embryos; but often it combines these purposes and adds to them that of a nursery. The last phase is illustrated by certain social insects, some birds, a few mammals, and in human society. In the lowest ranks of invertebrate life, and to some extent among animals of comparatively high organization, the eggs, or ‘spawn,’ are simply voided into the water or earth and left to survive or perish, unregarded by the parent. Some animals, however, produce comparatively few eggs, protected against many dangers by being placed within one or more envelopes or ‘capsules.’ (See Egg.) Another widespread method is that of retaining the embryo in the maternal body until it is able to shift for itself. This is seen in many invertebrates and in some fishes. These animals are therefore known as ovoviviparous.

Maternal Care of Eggs. An advance upon this is made by a large class of creatures which carry their eggs about with them until they hatch, and in some cases even continue to care for the young, although they make no nest. Examples of this are to be found in all classes of animals, from mollusks and crustaceans up to a few of the lowest birds; and some of the brooding habits and physical adaptations thus manifested are surprising. Thus the female argonaut (q.v.) has developed an elaborate boat-like shell in which her eggs and embryos rest secure; the violet-snail (q.v.) (Janthina) drags hers beneath a raft; and other instances are citable. Spiders' eggs are covered with silk, forming a bag or ball of various shapes and colors. (See Spider.) Crustaceans almost universally keep their eggs with them. Some insects inclose their eggs in packets and take care of them, much as do the crabs, but most insects simply deposit their eggs so that the resulting larvaæ shall be within reach of suitable food, and do not know what becomes of them. It is not until the highest grades of Hymenoptera are reached—the wasps, bees, and ants—that anything which may be called a ‘nest’ is made in preparation for the eggs or young, or any parental care is exerted. (See Ant; Bee; Wasp; Insect, paragraph Social Insects.) The equal of this is hardly to be found among vertebrates until man is reached—and even then only among men in a somewhat advanced stage of culture.

Fishes and Reptiles. Among fishes a certain amount of instinct is adapted to the best interests of the young. Thus many kinds migrate long distances to seek the water or food proper for the young, but, a suitable general surrounding having been obtained, little or no further care is taken. Only a few species build nests. Certain kinds make very crude nests, such as the hollow scooped out in the sand on some warm, clean, sunny bottom by the male sunfish, or the more elaborate structures of sticklebacks and gobies (qq.v.). Amphibians and reptiles rarely make anything which may be called a nest, but some care for their eggs in very curious ways elsewhere described.

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 Ratitæ 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. Among those a little higher in the scale, nests of sea-weed and coarse grass loosely put together make a home for the young. Most of the ducks and geese build nests of grass, and often include feathers from their own bodies, a habit carried to the extreme in the eider-duck (q.v.). Few of the wading birds build nests, the herons 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, in which the eggs are laid, the heat caused by the decay ripening them. Doves and pigeons usually build a very frail 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 mammal, especially the prairie dog. Parrots, woodpeckers, 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 nests known; and swifts extraordinary ones, consisting largely of mucilaginous saliva. (See Chimney-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 aesthetic 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 century—Rennie's Architecture of Birds (London, 1831). He divided his subjects into such classes as ground-nesters, squatters, and miners; builders of mounds, of umbrellas, of domes; masons; carpenters; platform-makers; basket-makers; weavers; tailors; felters; 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 Natural Selection (London, 1870) 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 materials most available. Wallace places birds' nests in two great classes—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 holes in trees or in banks and cliffs, as well as nests covered by the bird, such as the suspended 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 he believed, correlated with the color of the female. As he 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 so 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. Murray, and by J. A. Allen (Bulletin Nuttall Ornith. Club, vol. iii., Cambridge, 1878), and by others more recently, show that it is not so universal in its application or fully explanatory as its author considered it. The hypothesis was restated, with improvements, by Wallace, in Darwinism (New York reprint, 1889).

The more recent philosophic view, well summarized by Chapman (Bird Life, New York, 1898), is that, apart from and above the various considerations already mentioned, the necessity for protection of the eggs and young from physical accidents, loss of heat, and seizure by enemies is the real motive; and the superior excellence as cradles of the nests of birds of the higher orders is explained by the fact that these orders are ‘altricial’—that is, their young are born in a helpless condition, must be cared for by the parents for a considerable time, and hence both old and young need much better and safer quarters than do the ‘precocial’ birds, whose young (e.g. chickens) run about at birth and have no need of a nursery.

Wallace also treated of the belief formerly prevalent that birds work by instinct and never make any improvement during their lifetime in nest-building. He asserted that the chief mental faculties so exhibited by birds are the same in kind as those manifested by mankind in the formation of their dwellings; that is, essentially, imitation, and a slow and partial adaptation to new conditions. In answer to the objection that it is not so much the material as the form and structure of nests that varies, Wallace replied that such diversities may be explained in a great measure by the general habits of the species, the nature of their tools, the materials they can most easily obtain, and differences of habitat and needs that may have occurred within the period of existing species, due to changes in climate, the earth's surface, food, and so forth. Birds learn something, doubtless, in regard to the size, structure, and material of the nest of their own species before they leave it. Wallace quotes a number of cases of birds reared in the nests of other birds that sang only the song of the foster parent, learned while in the nest. Then, too, young birds do not always mate with birds of their own age, and the young bird learns nest-building from its more experienced mate. It is not unusual to see one bird of a pair, say an English sparrow, redisposing the material that the other bird has just put in place. Several observers have stated that young birds build less perfect nests than old birds, and Wallace quotes one instance in which some young chaffinches were taken to New Zealand and there set free. They built a nest in the new home which showed “very little of that neatness of fabrication for which this bird is noted in England.” It is an oft-repeated observation that the nests of the Baltimore oriole, when built near the habitations of man, differ in shape and structure from those in the wilds where twine and threads are not at hand, and where there is more necessity of concealment from hawks and snakes. The swallows and swifts of all parts of the world are quick to change their nesting places from hollow trees and rocky cliffs or caverns to the porches, barns, and chimneys of men's habitations, and changes in the style of their architecture follow. The nests of house wrens and purple martins vary with the situations chosen. The orchard oriole may build a shallow nest in stout branches or deep ones in swaying willows. Many similar instances of change in form and material might be adduced, “Children and savages imitate before they originate; birds, as well as all other animals, do the same,” so when the environment remains constant, the form and constructive material of birds' nests vary little.

PENSILE NESTS OF BIRDS

1. AUSTRALIAN FLOWER-PECKER (Dicæum hirundinaceum).	4. INDIAN TAILOR BIRD (Orthotomus sutorius).
2. EUROPEAN PENDULINE TITMOUSE (Ægithalus pendulinus).	5. RED-EYED VIREO (Vireo olivaceus).
5. BRAZILIAN CRESTED CACIQUE (Ostinops citrius).	6. BALTIMORE ORIOLE (Icterus galbula).

Brooding of Birds. The eggs of birds are hatched by the steady application of warmth for a sufficient time to mature the embryo to the stage when it breaks from the shell. This necessary warmth (about 105° F.) is secured by the bird covering the eggs with its body, ‘sitting’ upon or ‘incubating’ them almost continuously for a length of time which in a general way is proportioned to the bird's size. No very extended and accurate observations on this point have been recorded; the best are those by Evans in The Ibis (London) for 1891 and 1892. Broadly speaking, most of the small song-birds hatch their young in from 13 to 15 days, but the very smallest may take less time—the humming-bird, it is said, only 10 days. In canaries, it is from 15 to 18 days; in the common fowl, it is 21 days; in the duck, it is from 28 to 30 days; in the guinea-fowl, it is 28 or 29 days; in the turkey, 30 days; and in the swan, from 40 to 45 days. The emeu is said to sit 50 days. Small altricial birds usually begin sitting after the first egg is laid; but game-birds and water-fowl rarely begin to sit until the whole clutch is in the nest, so that the whole brood shall hatch simultaneously.

It is in most birds the function of the female to perform the duties of incubation, during which she is to a greater or less extent defended, fed, and cheered by her mate. Twice or oftener each day she leaves the nest for rest and to get food, and the male takes her place for an hour or two. It sometimes happens that if she is killed, the male concludes the process of incubation and cares for the young. In some groups he does the entire duty of sitting. This seems to be universally true of the ostrich and other ratite birds, and is the practice of the godwits, phalaropes, and certain other shore-birds. Both sexes join in the care of the young at first, but in most cases their education is gradually left entirely to the mother.

Nests of Mammals. Among the mammals, a ‘nest’ in the present sense of the word is not common. The female, when about to bring forth young, is either already in a den or lair which has been a family residence during the winter or is permanently so, or else requires no more accommodation than a retired corner in the midst of a thicket or beneath a sheltering rock. Squirrels, wood-rats, and mice (qq.v.), however, often construct in bushes and trees, or among tall grass or low brush, globular nests of leafy twigs or of grass in which the young are born. The ‘lodges’ of the beaver, muskrat, coypu, and the like, elsewhere described, are family houses in which the protection of the young is probably the prime desideratum. Hardly different, and by no means so elaborate, are the platforms or ‘nests’ of the anthropoid apes, and especially of the orangs (see Orang-utan), where the young are born, but in which they do not long remain. There is, however, little to choose between these structures, or their advantage to the young, and those of many nomadic savages, such as the aboriginal Bushmen of South Africa, the northern Australians, or the Indians of the Utah Basin and deserts of Arizona and Chihuahua.

Consult standard works on zoölogy, especially Cambridge Natural History, vols, iii.-x. (London, 1898-1002); and Newton, article “Nidification,” in Dictionary of Birds (London and New York, 1893-96). See also works cited under Egg.