The voice in mammals, including man, is produced in the voice-box, or larynx, in the upper part of the throat. The bird possesses a similar larynx; but its sounds and notes are formed in another voice-box, the syrinx, at the lower end of the windpipe, where it divides to send a bronchial tube to either lung. The syrinx is composed of firm walls derived from the rings of the trachea, or in part from the bronchi, and has within delicate membranes whose tension is controlled by slender muscles. Air expelled forcibly over these membranes produces sound which may be of many kinds, according to the species concerned. The adult turkey vulture (Cathartes aura), and the brown pelican (Pel ecanus occidentalis), have as their only note a sighing aspiration made by expelling the air unmodulated, though their young utter harsh calls in some variety, either in begging for food or in at tempting to repel possible enemies. The voiceless condition in the adult is unusual. The rhea sends forth a booming call, ventrilo quial in effect, that carries for long distances, the wedge-tailed shearwater utters a series of indescribable groans and shrieks, which combine with those of thousands of its kind to produce a vast volume of sound, the gull or tern calls in constant iteration with a note of harshest sound. In the highest order of birds, among the oscines or song-birds, song has reached high develop ment, and in many follows lines of human music sufficiently to give deep aesthetic pleasure. The male mockingbird (Mimus poly glottos) of America, is stirred by spring to a period of vocal utter ance that includes a varied repertoire of utterances peculiar to his own expression, as well as notes borrowed from tuneful neigh bours. In the height of the breeding season his efforts continue day and night in apparently ceaseless expression of virile energy. The nightingale (Luscinia megarhyncha) of Europe, a dweller of tangled copses. would be overlooked by many were it not for his impassioned outburst of song (which, contrary to popular belief, may be heard at all hours of day and night). The two just mentioned, with the addition of the hermit thrush and the sky lark, are the songsters of greatest renown among English-speaking peoples.
A number of bird-songs, even where they have variety of note, are frequently unpleasant to some human ears. Many com plain of the doleful cadence of the cooing of mourning doves (Zenaidura macroura), or are unpleasantly affected by the harsh chatter of the house sparrow. The song of the plant-cutter (Phytotoma rutila) of Argentina exactly resembles the creaking of two tree-limbs rubbing against one another in the wind. The song of the Henslow's sparrow (Passerherbulus /ienslowii) is a low double note barely audible at a hundred yards.
The song impulse is so predominant at the height of its period that it is given expression on the slightest disturbance. Birds awakened at night frequently sing for an instant as clearly as during the day, and song also may be used to express emotions of fear and anger.
Though modulated speech for the expression of abstract ideas may be peculiar to man, there is no question but that birds possess a rudimentary language in the sense that they use their calls to communicate with one another. A low call on the part of a parrot or paroquet at detection of a sound or sight that may denote danger will instantly cause the entire group of its companions to become motionless, or send them in screaming confusion into the air. The mother pheasant warns her young, who immediately
hide and cannot be found. The rooster, by rapid repetition of a certain note, calls the members of his harem to some supply of food. There are also cries of anger, and others that may be interpreted as conversational, that enable species of social habit to keep in touch with one another. Bird-calls are often intelligible to other creatures, as the alarm-call of a jay or plover will often startle deer or other game.
There are a number of birds that possess a strong imitative faculty which, in domesticated individuals, may be adapted to the mimicry of human sounds. Canaries and other finches may be taught to whistle a few notes of musical airs. The Amazon parrots are particularly adept at mimicry of the human voice, and similar ability is found in some macaws, paroquets and other parrots. Crows, jays and magpies also may learn to repeat a few words, as may starlings and mynahs. According to a widely current superstition the tongues of the latter birds must be split to enable them to articulate human speech, a belief for which there is no valid basis, whatever, and which, when practised, imposes a needless cruelty. This curious belief may be based on the fact that the tongue of crows and jays is naturally somewhat split.
The wing-membranes of the ancient reptilian pterosaur (see PTERODACTYL) were supported by elongated finger-bones, as are the wings of bats (though differently), but birds have developed another mechanism for flying, as the fore-limb, including the hand, has long feathers projecting from its posterior margin that are extended to form a supporting surface, by which flight is accomplished (see also BIRD). The hand is stiffened, being flex ible only at the wrist, the number of hand and finger-bones is reduced, and those that remain are partly fused together. The wing thus developed folds against the sides, so that it causes no embarrassment when the bird is at rest or is walking or climbing, but at the same time may be extended instantly should need or desire for flight arise. It appears thus perfectly adapted for its purpose and in utility (though not in speed) eclipses the aero planes of man.