white.) With respect to the third case, namely, that of the young
having an intermediate character between the summer and winter adult
plumages, Yarrell (45. History of British Birds, vol. i. 1839, p.
159.) insists that this occurs with many waders. Lastly, in regard to
the young differing greatly from both sexes in their adult summer and
winter plumages, this occurs with some herons and egrets of North
America and India, the young alone being white.
I will make only a few remarks on these complicated cases. When the
young resemble the females in their summer dress, or the adults of both
sexes in their winter dress, the cases differ from those given under
Classes I. and III. only in the characters originally acquired by the
males during the breeding-season, having been limited in their
transmission to the corresponding season. When the adults have a
distinct summer and winter plumage, and the young differ from both, the
case is more difficult to understand. We may admit as probable that the
young have retained an ancient state of plumage; we can account by
sexual selection for the summer or nuptial plumage of the adults, but
how are we to account for their distinct winter plumage? If we could
admit that this plumage serves in all cases as a protection, its
acquirement would be a simple affair; but there seems no good reason
for this admission. It may be suggested that the widely different
conditions of life during the winter and summer have acted in a direct
manner on the plumage; this may have had some effect, but I have not
much confidence in so great a difference as we sometimes see between
the two plumages, having been thus caused. A more probable explanation
is, that an ancient style of plumage, partially modified through the
transference of some characters from the summer plumage, has been
retained by the adults during the winter. Finally, all the cases in our
present class apparently depend on characters acquired by the adult
males, having been variously limited in their transmission according to
age, season, and sex; but it would not be worth while to attempt to
follow out these complex relations.
CLASS VI. THE YOUNG IN THEIR FIRST PLUMAGE DIFFER FROM EACH OTHER
ACCORDING TO SEX; THE YOUNG MALES RESEMBLING MORE OR LESS CLOSELY THE
ADULT MALES, AND THE YOUNG FEMALES MORE OR LESS CLOSELY THE ADULT
FEMALES.
The cases in the present class, though occurring in various groups, are
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