Birds (aves), a class of vertebrate biped animals, exclusively oviparous, and with very few exceptions covered with a feathered coat, adapted more or less perfectly for flight. They have frames penetrated through all their parts by air cells, which facilitate motion by imparting lightness. By means of nests, which serve as substitutes for internal organs of reproduction, they develop their young after the exclusion of the ova. The last two peculiarities distinguish birds from all other animals. The families which have not the power of flight are few both in regard to the number and varieties of species, and to the individuals composing them. They are all formed either for motion on the land or in the water exclusively. In all these instances the feathery coverings are incompletely developed, possessing a proximate ambiance to the hairy covering of certain land and water animals. The ostrich and the penguin may be named as typical of these two distinct forms of exception, both in regard to their inability to raise themselves into the air and their exceptional hair-like plumage. - In the internal organization of the entire class of birds there are other and more noticeable anatomic peculiarities. Their skulls are without the sutures that are found in mammalia, forming consolidated bones.

These are joined to the neck or spinal column by a joint, so constructed as to give freedom of motion in horizontal and lateral directions, without danger of dislocation or injury. In the place of teeth they have upper and lower jaws, forming unitedly the bill, and composed of a hard horny substance. In several families of birds, as the parrots, the upper part of the bill is articulated with the skull. More commonly the skull and upper jaw are united by means of an elastic bony plate, by the interposition of which the brain is protected from injuries to which it would otherwise be exposed. The upper extremities of birds, homologous with the arms or fore legs of other animals, differ essentially in never being: used as prehensile organs, or for motion in contact with the earth, as in walking or running. Their use is almost exclusively for flight, and they serve as the basis of the wings. The cervical vertebra of birds are more numerous than those of mammals. In the latter their number is uniformly 7, while in birds there are never fewer than 10, and in some instances there are as many as 28. The dorsal vertebrae are more fixed and limited in their motion than the cervical, and are usually 10 in number, rarely 11, and in some instances only 7 or 8. The pelvis in birds is a simple elongated plate, open below, terminated by the rump, which supports the tail feathers.

Parts of a Bird

Parts of a Bird. - 1. Skeleton. 2. Nictitating Membrane. 3. Brain. 4. Sternum or Breast Bone.

The breast bone or sternum is perhaps the most noticeable feature in the bony skeleton of birds. It is also one of the most important parts of the osseous framework, as it forms the base for the insertion of the most powerful of the muscles of flight. Its prolongation or crest determines with infallible accuracy the degree of power of flight of its possessor, and is entirely wanting in those destitute of the power of raising themselves in the air. The merrythought (ferciila) should be here mentioned as another peculiarity in birds of flight, and wanting only in those pot possessed of that power. The bony framework of the lower extremities comprises a thigh bone, two leg bones, a metatarsal or ankle bone, and the bones of the toes. The last vary in number, and terminate in nails, of greater or less importance in the animal economy, according to the habits of the family possessing them. The variations in the mechanism of the lower extremities are often very curious and striking. The birds which roost, and more especially those which are in the habit of standing long at a time upon one leg, are enabled, by the remarkable arrangement of the bones and the muscles attached to them, to do either with very little effort or fatigue.

As might be expected, in birds of vigorous flight we find the pectoral muscles presenting the greatest development. These often exceed all the other muscles in weight and bulk. The great pectoral and the middle pectoral are antagonistic forces, alternately depressing and elevating the wings, while the small pectorals, or third pair, aid in varying the manner and character of the flight. The muscles of the lower extremities vary greatly with the habits of the bird, and especially according as they are climbers, waders, swimmers, perch-ers, etc. Besides their muscular integuments, all birds have horny beaks and nails, a fleshy cere at the base of the bill, and scaly coverings to the lower extremities, wherever they are bare. Their peculiar covering, found more or less perfectly in the whole class, and in no other kind of animals, is their plumage. In certain families, as that of the ostrich, the plumage makes a remarkably close approach to the hairy coverings of land mammals. In other families, such as the divers, the alcadae, the guillemots, etc, the plumage more nearly approaches the furry coats of the otter and the seal. The plumage of all birds of this order is close, oily, and often glossy, and the skin is moreover covered with a thick layer of down.

In the young of birds the proximate resemblance of their plumage to the hairy covering of mammals is even more marked. The bills of birds enable the raptorial families to tear their pr3y into fragments; they supply to the fly-catcher, the swallow, and the whip-poor-will exquisitely contrived insect traps; they give to the woodcock, the snipe, and other waders, the power of determining what is suitable for food, with no other aid than the most delicately sensitive nervous membranes of their long probe-like jaws. - In birds, the alimentary canal comprises an oesophagus, a crop, a membranous stomach, a gizzard, an intestinal canal, and a cloaca, in which the urinary ducts also terminate. The gizzard is a powerful organ in promoting digestion, especially with gallinaceous and other graminivorous birds. - That peculiarity of structure, however, which most fully distinguishes this from every other class of animals, is the immediate and constant connection of the lungs with numerous air cells that permeate the entire frame, extending even throughout the bony portions. These membranous air cells occupy a very considerable portion both of the chest and of the abdomen, and have the most direct and uninterrupted communication with the lungs. The long cylindrical bones are so many air tubes.

Even the flat bones are occupied by a cellular bony network, filled with air. The large bills in certain genera, even the very quill feathers when fully developed, receive more or less air from the lungs, at the pleasure of the birds. By these means the erectile crests of a number of species are alternately depressed or elevated. The design of these chains of air cells, penetrating into every portion of the structure of birds, is obvious. Lightness of the body for motion in the air or water, or on the land, is indispensable. Hence we find in birds of the highest and most rapid flight the largest supply of air cells. This pneumatic apparatus is also supposed to assist materially in the oxidation of the venous blood, and the air contained in the cells is presumed to operate upon the blood vessels and lymphatics in contact with them. The volume of air which birds are thus enabled to introduce into their bodies, and the ease and power with which they can at will expel it, taken in connection with their peculiar organs of voice, explain how some of the smallest members of the class, as the common canary bird or the black-poll warbler of North America, are enabled to give utterance to such powerful notes, and to continue them so long without any apparent effort.

The construction of the larynx in this class is very peculiar, bearing a remarkable resemblance to certain wind instruments. This organ is made up of two parts, the true rima glottidis, at the upper part of the windpipe, and the bronchial larynx, which is furnished with a peculiarly tense membrane, performing the same duty as the reed in the clarinet. The song of birds is the expression of amorous desire. It is confined to the males, and in a state of nature is heard only during the breeding season. Many birds have no power of song. The call of birds, however, is common to both sexes and all species, and is their universal language. Many birds, which are mute in the countries to which they migrate in the winter months, and have the reputation of being entirely voiceless, are clamorous when they breed, as is the case with the European woodcock (scolopax rusticola), and the jacksnipe, or judcock (scolo-pax gallinula). Some birds are known by their clang of tongues in their migrations, clamoring in order to regulate their squadrons, as wild geese, cranes, and many of the waders, which rise voiceless when they are alarmed by the sportsman, and feed in the daytime silent. Others are, so far as we know, silent at all times, except when they spring upon the wing, in any sudden alarm.

Some again, as the passenger pigeons, make their migrations in silence, take wing in silence when alarmed, yet when alone in the woods make the solitudes sonorous; others, like rooks, are habitually noisy, especially in the breeding season, yet rise in flocks without sound or signal. In some species which do not ring, there is an amatory call which answers the purpose of song, peculiar to the male bird during the season of the female's incubation, as the clear double whistle of the American quail, the cry of the cuckoo, the cooing of the dove, the harsh craik of the landrail, and the kek-kek-kek of the male of the English snipe, as it is falsely called in the United States (seotopax Wilsonii), which is either discontinued, or changed into something different, when the season and the desire for reproducing their species have passed away. As a general rule, aquatic fowl are more noisy than land birds, sea fowl than fresh-water birds, nocturnal than diurnal birds, domesticated fowls than those in a state of nature, birds which congregate than those of solitary habits, and, with the exception of common poultry, migratory birds, which pass much of their time on the wing, than those which dwell on the ground.

Nevertheless, while some sea birds which congregate are deafening in their clangor, they fly totally independent one of the other, not regulating their movements by signals of any kind; others, as many varieties of the tringa, scolo-pacida, and charadriadae, while they utter no sounds, yet wheel as regularly and orderly, in obedience to some concerted signal, as a well disciplined regiment of horse. And again, while some migratory birds are vociferous in the extreme, others are totally silent, and some non-migratory species, such as jackdaws and rooks, exceed all others in fondness for their own voices. - The large proportionate development of the brain and of the nervous system of birds is another distinguishing feature of their organization. In many cases they exhibit an apparent superiority to the corresponding organs in mammalia of the same relative size and weight. Thus, for instance, while in man the size of the brain in proportion to that of the whole body varies from 1/22 to 1/33 part, that of the common canary bird" is X. There are, however, great variations in this respect in different families and even in different genera of the same families.

Thus, while the brain of the goose is 1/360 of the entire body, that of the eagle is 1/260 and that of the common European sparrow is 1/25. It differs chiefly from the same organ in mammalia in the presence of certain tubercles corresponding to the corpora striata of other animals, and the absence of several parts found in the brains of the latter. - The senses of sight, smell, and hearing are supposed to be most acute in a large proportion of the families of the class, much more so than that of taste, which is found well developed in only a few families, and still more than that of touch, which is presumed to be totally wanting. The organs of sight are of great proportionate magnitude, and occupy a large proportion of the cerebral developments. They are constructed with a wonderful contrivance not inaptly compared with so many peculiar kinds of "self-adjusting telescopes "

Birds 0200343

1. Digestive Apparatus: c, Crop; g, Gizzard, t. Trachea. b, b. Bronchial Tubes. l, l. Lungs. 2. Bonos of the Wing.

They are also all provided with a very curious apparatus called the nictitating membrane. This is a fold of the tunica conjunctiva, so arranged as to be capable of being drawn out to cover the eye like a curtain, and to be withdrawn at will, enabling the possessor to meet the brightest rays of the sun undazzled by its brilliance, and protecting the organ from injuries. With only a few exceptions, birds have no external organs of hearing corresponding to an ear. We find instead the aperture called meatus avditorius. The internal membranes of this organ are connected with each other by means of the air cells of the skull, and have but a single auditory bone. Among different authors there is much diversity of opinion in regard to the development of the sense of smell in birds. The experiments of Audubon and Bachman would seem to prove that, even in those families in which this sense is presumed to reach its highest point of perfection, the members are directed by sight rather than by smell to their prey. Still it is quite certain that they possess certain nervous developments corresponding to olfactory organs, which, if not designed for smell, possess no very apparent purpose.

The sense of taste has a limited degree of development in a few families, such, for instance, as the divers, the waders in part, and the several families of humming birds, honey-suckers, and a few others. As a general rule it is very imperfect, or even wholly wanting. (For the character of the earliest birds, see ArchAEopteryx, and Fossil Footprints.) - The various contrivances and instinctive expedients, by means of which the entire class of ares develop the germs of their mature or perfect ova, are remarkable as well as distinguishing features in the economy of their propagation. They are peculiar to the class, and are without any known exceptions. They are shared with them by no other class of animals, with only occasional but remote approximations, apparent exceptions rather than real. Every individual of the entire class deposits the matured egg without any distinguishable development of the young bird. Lightness and buoyancy of body, whether for flight in the air or for freedom of motion on land or in water, are essential prerequisites in the animal economy of all the various families of the class. So, to nearly the same extent, is also their abundant reproduction.

The vast numbers of their enemies, and the many casualties to which they are exposed, render a large and constant propagation necessary for their preservation. It is quite evident that any habit at all corresponding with the gestation of viviparous animals would be inconsistent with both of these requirements. It would destroy lightness of body, prevent freedom of motion, expose to innumerable dangers from enemies, hinder from procuring food, and make fecundity an impossibility. Thus the common quail or partridge (ortyx Virginiana) of the Atlantic states has been known to have 36 eggs in a single nest. Before maturity the product of this nest exceeds in weight their parent at least 20 fold. To provide for these, or but one of them, by internal organs of development, would be impossible. The nests correspond in their uses to the uterine organs of reproduction of mammalia, and yet more to the marsupial pouches of certain Australian quadrupeds. They serve as external organs indispensable to the development of the immature young, from the first appearance of the germ in the egg to a maturity more or less advanced, and varying greatly with the family; from the ostrich that comes into the world able to shift for itself from the very shell, to the blind and naked offspring of other families that are utterly helpless when first hatched.

For this development of the young birds there are two essentials - the external receptacle which, though not always with exactness, we call nests, and the application of a certain nearly fixed or uniform amount of caloric. In nearly all cases the latter is generated by contact with the bodies of the parent birds. In some it is aided by the heat of the sun. In a few instances it is effected by heat derived from vegetable decomposition, or from the sun's rays, without any parental intervention after the deposition of the egg. - Attempts have been made, with partial success, to classify the various architectural contrivances, or their substitutes, to be found connected with the nesting and incubation of birds. According to the system of Prof. James Rennie of King's college, London, the entire class are ranged in 12 groups: miners, ground builders, masons, carpenters, platform builders, basket makers, weavers, tailors, felt makers, cementers, dome builders, and parasites. The objections to this arrangement are, that it is imperfect in itself, and that it corresponds to none of the usual systems of ornithological classification.

The large number of species which, without being miners or carpenters, invariably occupy for their nests corresponding sites, namely, holes in the earth or hollow trees, have no appropriate place. Some of these have been improperly classed as parasites. Nor is there a well defined place for the large variety of species belonging to every order which resort to the bare ground, making no perceptible nest, or for that remarkable familv of Australian birds, the mound builders, which combine something both of the miner and the ground builder. It seldom if ever conforms, in a single family even, with any known classification. Thus, the hawks are platform builders, ground builders, occupants of hollow trees, etc.; the swallows are miners, cementers, dome builders, masons, etc. - The mining birds compose a very large group, belonging to nearly every order, and having no other common peculiarity. They may be divided into two well marked subdivisions: the true miners, which excavate holes for themselves, in which they construct their nests; and those which, without mining, occupy sites precisely similar. Of these a portion are supposed to be parasitic, availing themselves of the labors of others.

Among the true miners may be named the common bank swallow, found nearly throughout the habitable globe, the bee-eaters of Europe and Asia, and the whole genus known as storm petrels or mother Carey's chickens; as also the several genera of puffins, kingfishers, penguins, etc. Among miners only by occupancy may be named the wood wren and the winter wren of North America, the black guillemot, and the burrowing owls of North and South America. The last are parasitic miners, occupying invariably holes dug by other animals. - The ground builders include by far the largest group of birds of every order, and nearly of every family, and cannot be defined with exactness. In it must be classed many which build no nest; others that do or do not construct nests, according to circumstances; those which build on the ground usually, but frequently elsewhere; some that are usually ground builders, but at times true miners, like the skylark of Europe, etc. The nighthawks and whip-poor-wills of America make no nest, the former depositing their eggs upon the bare earth, always selecting a site corresponding in color to their eggs, the latter selecting dried leaves as better suited to the same purpose of concealment.

A very large proportion of the shore birds, waders, gulls, etc, make use of the bare sand, with only a slight excavation for a nest. Others of the same species are more painstaking, and construct well formed nests. The herring gulls usually build a slight nest on the ground, but, after having been repeatedly robbed by eggers, the same birds are known to construct large and elaborate nests in trees or on precipitous cliffs. The mound builders of Australia (see Bnusn Turkey) combine in part the habits of the miners with those of* the ground builders, in a manner peculiar to that remarkable family. Among the true ground builders may be cited nearly all the vultures, the entire sub-family of circidae or hen-harriers, the zonotrichm or song sparrows of America, nearly all the waders, ducks, geese, swans, gulls, terns, etc, with more or fewer representatives in every order. - The birds classed as masons are comparatively few in number of species. They are so called because they construct their nests, in whole or in part, with walls, coverings, barricades, etc, of mud or clay. Of this class the cliff swallow of North America is one of the most remarkable examples.

The house swallows both of Europe and America, the thrush and blackbird of Europe, the robin and the pewit flycatcher of North America, are among the most familiar examples. The baker bird of South America, the most skilful and remarkable of this class, constructs a nest in the most exposed situations, but at a considerable height, hemispherical, or in the form of a baker's oven. The opening of this nest is lateral, and is twice! as high as it is wide, and the interior is divided into two chambers by a partition beginning at the entrance. - The true carpenters are also a comparatively small group, consisting of those which excavate by their own labor holes tor their nests in trees. The large and widely distributed family of woodpeckers are the most familiar examples of the carpenter bird. With them are also classed the toucans of South America, the tomtit-, the wrynecks, and the nuthatches. Among the more common examples of the birds which, without being true carpenters, resort to similar places for their nests, may be mentioned the sparrowhawk, the bluebird, the purple martin, the white-bellied swallow. and the house wren of North Amer-reral species of owls, and many other. - The platform builders are a small but distinct class, embracing most of the hawk tribe, the wood pigeons, the cuckoos of America, etc.

All the eagles are true platform builders, and many of them construct elaborate and remark-able nests. The nest of the white-headed eagle is a massive structure, sometimes forming an exact cube five feet square. The martial eagle of southern Africa also constructs a large platform, said to be able to support the largest man. These nests are perfectly flat, with no other security against the eggs (always few in number) rolling off than the constant presence of one of the parents. The common passenger pigeon, the turtle dove, and the yellow-billed cuckoo of North America are the most familiar examples of this class; as also in Europe are the wood pigeons, the ringdoves, the herons, and the storks. - Another larger class, whose architectural accomplishments are even more remarkable, are the basket-makers. Many of these exhibit an elaboration and an ingenuity beyond the power of human skill to imitate.. The vireos of North America weave a cup-shaped basket nest, pendent from some convenient twig, the leaves of which conceal them from enemies.

The European bullfinch, the American mocking bird, the red-winged blackbird, the yellow-headed troopials of North America, the ravens, crows, and magpies, and the cyanotis omnieolor of Chili, may be mentioned as among the more familiar or remarkable of this interesting group. The last-named bird attaches a nest of singular beauty and elaborateness to the stems of the large reeds of that country, constructed to resemble so closely the ripened seed vessels of the plant as to deceive even the most wary. The locust-eating thrush of southern Africa builds a large basket fabric, containing many cells or separate nests, from 6 to 20 in number, the joint products of and occupied by as many pairs. The pensile groasbeak swings its basket neat from a pendent twig over a running stream, and makes its entrance from the bottom The sociable groasbeaks unite in the construction of a large, basket-like cluster of nests, sometimes containing 200 or 300 in a single structure. The weavers are closely allied to the preceding class, differing chiefly in their more pensile nests, and in the superior nicety of their structure. The weaver oriole of Senegal is one of the most remarkable of this class.

The Baltimore oriole of America, the Indian sparrow of southern Asia, the crested fly-catcher of southern Africa, and the yellowhammer of Europe, are among the more familiar and distinguishing instances of the weavers. Hardly distinguishable from the two preceding groups are the few species classed as tailors. The orchard oriole of America is hardly entitled to be so classed, though usually quoted as a true tailor. The best known instance is that of the sylvia sutoria of the eastern continent, which sews a dead leaf to a living one, and between them constructs its tiny nest. The blue yellow-back warbler of America is another remarkable tailor, though its wonderful skill is as yet little known or appreciated. - The felt makers form quite a large and well marked group of artificers among birds. These arrange the materials of their nests, though more loosely, in the same manner as that in which are put together the fibres of felt. These materials are, to all appearances, corded together. How this is done cannot be satisfactorily explained.

The chaffinch of Europe, the goldfinch of America, the canary bird, and the whole family of humming birds, may be given as exemplifications of this peculiar and interesting group. - The cementers compose a very small but well distinguished class, all the members of which, so far as is at present known, belong to the family of swallows. These birds secrete, from glands on each side of the head, a strongly adhesive glue, which is dissolved in their saliva, and with this unite the materials of their nests, and fasten them to their proposed sites. The chimney swallow of North America is the most familiar example of this group, while the esculent swallow of the East is the most remarkable. - The dome builders might without inconvenience be merged in the several groups of weavers and basket-makers. They consist of a large number of species belonging to a great variety of families, which construct covered nests, entered by holes in the side. These nests are more common in tropical than in cold countries. The marsh wrens, several of the syhicolce (as the Maryland yellow-throat), the golden-crowned thrush or oven bird, the meadow lark, and the quail, of North America, are among the most familiar representatives of this group on this continent.

In Europe it embraces the common wren, the chiff-chaff, the hay-bird, the wood wren, the sparrow, the magpie, and the bottle-tit, among its best known members. - The last group is one which it is not easy to classify. The true parasites, those which, like the cuckoo of Europe, the cow blackbirds of North America, and its congener of South America, never rear their own young, but intrude their offspring upon strangers, always laying their eggs in the nests of other species, are a small but well marked class. The larger number which resort to the chosen sites of other birds, but build their own nests and rear their own young, are less clearly defined, because they are not uniformly parasitic in their habits. Of this latter class, the house sparrow of Europe as often makes its own nest as it seizes upon that of another species. Nearly or quite all of this class, usually marked as parasites, are so only occasionally, and by force of circumstances. The true members of the group are not many, and, so far as is at present known, are confined to the two genera cuculus, or true cuckoos, and molothrus, or cow birds. - According to Mr. A. R. Wallace, birds' nests may be divided into two classes: those which are exposed or imperfectly concealed, and those which are covered, or so placed that the sitting bird is effectually hidden.

Birds may also be divided into two groups, according to the difference of coloration in the sexes: in some species varied and brilliant colors occur in both sexes; in others, a more numerous class, the male is brighter than the female. With but few exceptions, Mr. Wallace finds that birds of conspicuous color build concealed nests, while in species where the female is dull the nest is fully exposed. Among American birds in which the females are bright and conspicuous, and which accordingly conceal their nests, or make them of a color to deceive, or of a form or depth to hide the sitting bird, are: the kingfisher, woodpecker, Carolina parrot, Baltimore oriole, humming birds, magpie, many bright warblers, sparrows, and finches, meadow lark, Zenaida dove, wild turkey, quail, Canada, pennated, and willow grouse, and summer duck. Among our birds in which both saxes are dull, and a concealed nest unnecessary, are the thrushes and orioles, and the passenger pigeon. Among those in which the male is bright and the female dull are the yellow-breasted warbler, goldfinch, grossbeaks, scarlet tanager, redstart, bobolink, red-winged blackbird, kingbird, many flycatchers, and the ruffed grouse.

Another interesting coincidence is that in the concealed or concealing nests, the eggs, as a general rule, are white, as with the owls, swallows, kingfishers, woodpeckers, humming birds, quails, and doves. - See "Proceedings of the British Association for the Advancement of Science," for 1867, and "Proceedings of the Boston Society of Natural History," vol. xi., pp. 319-321, 1867. (For the systematic classification of birds, and the history of the science, see Ornithology).