The
act of singing is evidently a pleasurable one; and it probably serves as
an outlet for superabundant nervous energy and excitement, just as
dancing, singing, and field sports do with us. It is suggestive of this
view that the exercise of the vocal power seems to be complementary to
the development of accessory plumes and ornaments, all our finest
singing birds being plainly coloured, and with no crests, neck or tail
plumes to display; while the gorgeously ornamented birds of the tropics
have no song, and those which expend much energy in display of plumage,
as the turkey, peacocks, birds of paradise, and humming-birds, have
comparatively an insignificant development of voice. Some birds have, in
the wings or tail, peculiarly developed feathers which produce special
sounds. In some of the little manakins of Brazil, two or three of the
wing-feathers are curiously shaped and stiffened in the male, so that
the bird is able to produce with them a peculiar snapping or cracking
sound; and the tail-feathers of several species of snipe are so narrowed
as to produce distinct drumming, whistling, or switching sounds when the
birds descend rapidly from a great height.
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