Song, call notes, and certain mechanical sounds constitute the language of birds. Song is produced in the syrinx, whose firm walls are derived from the rings of the trachea, and is modified by the larynx and tongue. The membranes of the syrinx are controlled by slender muscles; in the oscines, or song birds, there may be as many as eight pairs of these muscles, whereas other birds have four or fewer. The greater development permits intricate patternings of sound (rare outside the oscines) that express a wide range of reactions, from pleasure to distress. Recognizable by humans and other animals as well as by other birds, the various calls are classified as flight, feeding, nest, flock, aggressive, alarm, and territorial-defense calls. Song is usually confined to the male and is at its height during the breeding season. Experiments have shown that hormone secretion in the male is directly connected with his propensity to song as well as with his selecting a territory for courtship and breeding. Among the oscines are such superior singers as the southern mockingbird, the hermit and wood thrushes, the purple and house finches, the canyon wren, and the European skylark and nightingale. Natural mimicry is characteristic of the mimic thrushes, the jays and crows, and the starlings, while birds with imitative faculties developed in captivity are canaries, finches, parrots, ravens, crows, and mynas. There is evidence that songs are learned and that certain calls are inherited. Most birds have preferences regarding the place from which they sing, e.g., fence posts, treetops, thickets, the forest floor, or on the wing. Mechanical sounds include the drumming of the grouse, the tattooing of the woodpecker, and the clattering of the stork.
- See E. A. Armstrong, A Study of Bird Song (2d. enl. ed. 1973);.
- Bird Sounds and Their Meaning (1984). ,