The Descent of Man

Belt believes ('The Naturalist in Nicaragua,' p.
197) that the principal use of the beak is as a
defence against enemies, especially to the female
whilst nesting in a hole in a tree.) The naked
skin, also, at the base of the beak and round the
eyes is likewise often brilliantly coloured; and
Mr. Gould, in speaking of one species (52.
Rhamphastos carinatus, Gould's 'Monograph of
Ramphastidae.'), says that the colours of the
beak "are doubtless in the finest and most brilliant
state during the time of pairing." There is
no greater improbability that toucans should be
encumbered with immense beaks, though rendered
as light as possible by their cancellated
structure, for the display of fine colours (an
object falsely appearing to us unimportant),
than that the male Argus pheasant and some
other birds should be encumbered with plumes
so long as to impede their flight.
In the same manner, as the males alone of various
species are black, the females being dull-