The Descent of Man

irds of prey, before it has acquired its summer
dress: see Wilhelm von Wright, in Lloyd, 'Game
Birds of Sweden,' 1867, p. 125.), serve during
both seasons as a protection. When the
difference between the two plumages is slight it
may perhaps be attributed, as already remarked,
to the direct action of the conditions of life.
But with many birds there can hardly be a
doubt that the summer plumage is ornamental,
even when both sexes are alike. We may conclude
that this is the case with many herons,
egrets, etc., for they acquire their beautiful
plumes only during the breeding-season. Moreover,
such plumes, top-knots, etc., though
possessed by both sexes, are occasionally a little
more developed in the male than in the female;
and they resemble the plumes and ornaments
possessed by the males alone of other birds. It
is also known that confinement, by affecting the
reproductive system of male birds, frequently
checks the development of their secondary
sexual characters, but has no immediate in-