The Descent of Man

Sclater, in 'Proceedings, Zoological Society,'
1860, p. 90, and in 'Ibis,' vol. iv. 1862, p. 175.
Also Salvin, in 'Ibis,' 1860, p. 37.)
The diversity of the sounds, both vocal and
instrumental, made by the males of many birds
during the breeding-season, and the diversity
of the means for producing such sounds, are
highly remarkable. We thus gain a high idea of
their importance for sexual purposes, and are
reminded of the conclusion arrived at as to insects.
It is not difficult to imagine the steps by
which the notes of a bird, primarily used as a
mere call or for some other purpose, might
have been improved into a melodious love
song. In the case of the modified feathers, by
which the drumming, whistling, or roaring
noises are produced, we know that some birds
during their courtship flutter, shake, or rattle
their unmodified feathers together; and if the
females were led to select the best performers,
the males which possessed the strongest or