CHAPTEK V. THE VOICE OF BIRDS.* Aside from the pleasure to be derived from the calls and songs of birds, their notes are of interest to us as their medium of expression. N^o one who has closely studied birds will doubt that they have a language, limited though its vocabulary may be. Song. — Song is a secondary sexual character, generally restricted to the male. With it he woos his mate and gives voice to the joyousness of nesting time. In some instances vocal music may be replaced by instrumental, as in the case of the drumming wing-beat of the Grouse, or the bill-tattoo of the Woodpeckers, both of which are analogous to song. The season of song corresponds more or less closely with the mating season, though some species begin to sing long before their courting days are near. Others may sing to some extent throughout the year, but the real song period is in the spring. Many birds have a second song period immediately after the completion of their postbreeding molt, but it usually lasts only for a few days, and is in no sense com- parable to the true season of song. This is heralded by the Song Sparrow, whose sweet chant, late in February,
- See Witchell, The Evolution of Bird Song (Macmillan Co.).
Bicl^nell, A Study of the Singing of Our Birds; The Aiik (New York city), vol. i, 1884, pp. 60-71, 12G-140, 209-218, 322-332 ; vol. ii, 1885, pp. 144-154, 249-262.
