distinguished; the females and the young from the distinct countries
being indistinguishable, and therefore absolutely unchanged. This is
the case with certain Indian chats (Thamnobia), with certain
honey-suckers (Nectarinia), shrikes (Tephrodornis), certain kingfishers
(Tanysiptera), Kalij pheasants (Gallophasis), and tree-partridges
(Arboricola).
In some analogous cases, namely with birds having a different summer
and winter plumage, but with the two sexes nearly alike, certain
closely-allied species can easily be distinguished in their summer or
nuptial plumage, yet are indistinguishable in their winter as well as
in their immature plumage. This is the case with some of the
closely-allied Indian wagtails or Motacillae. Mr. Swinhoe (6. See also
Mr. Swinhoe, in Ibis, July 1863, p. 131; and a previous paper, with
an extract from a note by Mr. Blyth, in Ibis, January, 1861, p. 25.)
informs me that three species of Ardeola, a genus of herons, which
represent one another on separate continents, are most strikingly
different when ornamented with their summer plumes, but are hardly, if
at all, distinguishable during the winter. The young also of these
three species in their immature plumage closely resemble the adults in
their winter dress. This case is all the more interesting, because with
two other species of Ardeola both sexes retain, during the winter and
summer, nearly the same plumage as that possessed by the three first
species during the winter and in their immature state; and this
plumage, which is common to several distinct species at different ages
and seasons, probably shews us how the progenitors of the genus were
coloured. In all these cases, the nuptial plumage which we may assume
was originally acquired by the adult males during the breeding-season,
and transmitted to the adults of both sexes at the corresponding
season, has been modified, whilst the winter and immature plumages have
been left unchanged.
The question naturally arises, how is it that in these latter cases the
winter plumage of both sexes, and in the former cases the plumage of
the adult females, as well as the immature plumage of the young, have
not been at all affected? The species which represent each other in
distinct countries will almost always have been exposed to somewhat
different conditions, but we can hardly attribute to this action the
modification of the plumage in the males alone, seeing that the females
and the young, though similarly exposed, have not been affected. Hardly
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