classes, on the young having retained a former or ancient state of
plumage, whilst the old of both sexes have acquired a new one. When the
adults are bright coloured, we may conclude from the remarks just made
in relation to the scarlet ibis and to many herons, and from the
analogy of the species in the first class, that such colours have been
acquired through sexual selection by the nearly mature males; but that,
differently from what occurs in the first two classes, the
transmission, though limited to the same age, has not been limited to
the same sex. Consequently, the sexes when mature resemble each other
and differ from the young.
CLASS IV. WHEN THE ADULT MALE RESEMBLES THE ADULT FEMALE, THE YOUNG
OF BOTH SEXES IN THEIR FIRST PLUMAGE RESEMBLE THE ADULTS.
In this class the young and the adults of both sexes, whether
brilliantly or obscurely coloured, resemble each other. Such cases are,
I think, more common than those in the last class. We have in England
instances in the kingfisher, some woodpeckers, the jay, magpie, crow,
and many small dull-coloured birds, such as the hedge-warbler or
kitty-wren. But the similarity in plumage between the young and the old
is never complete, and graduates away into dissimilarity. Thus the
young of some members of the kingfisher family are not only less
vividly coloured than the adults, but many of the feathers on the lower
surface are edged with brown (27. Jerdon, Birds of India, vol. i. pp.
222, 228. Gould s Handbook to the Birds of Australia, vol. i. pp.
124, 130.), a vestige probably of a former state of the plumage.
Frequently in the same group of birds, even within the same genus, for
instance in an Australian genus of parrakeets (Platycercus), the young
of some species closely resemble, whilst the young of other species
differ considerably, from their parents of both sexes, which are alike.
(28. Gould, ibid. vol. ii. pp. 37, 46, 56.) Both sexes and the young of
the common jay are closely similar; but in the Canada jay (Perisoreus
canadensis) the young differ so much from their parents that they were
formerly described as distinct species. (29. Audubon, Ornith.
Biography, vol. ii. p. 55.)
I may remark before proceeding that, under the present and next two
classes of cases, the facts are so complex and the conclusions so
doubtful, that any one who feels no especial interest in the subject
had better pass them over.
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