We may now consider the classes of cases, under which the differences
and resemblances between the plumage of the young and the old, in both
sexes or in one sex alone, may be grouped. Rules of this kind were
first enounced by Cuvier; but with the progress of knowledge they
require some modification and amplification. This I have attempted to
do, as far as the extreme complexity of the subject permits, from
information derived from various sources; but a full essay on this
subject by some competent ornithologist is much needed. In order to
ascertain to what extent each rule prevails, I have tabulated the facts
given in four great works, namely, by Macgillivray on the birds of
Britain, Audubon on those of North America, Jerdon on those of India,
and Gould on those of Australia. I may here premise, first, that the
several cases or rules graduate into each other; and secondly, that
when the young are said to resemble their parents, it is not meant that
they are identically alike, for their colours are almost always less
vivid, and the feathers are softer and often of a different shape.
RULES OR CLASSES OF CASES.
I. When the adult male is more beautiful or conspicuous than the adult
female, the young of both sexes in their first plumage closely resemble
the adult female, as with the common fowl and peacock; or, as
occasionally occurs, they resemble her much more closely than they do
the adult male.
II. When the adult female is more conspicuous than the adult male, as
sometimes though rarely occurs, the young of both sexes in their first
plumage resemble the adult male.
III. When the adult male resembles the adult female, the young of both
sexes have a peculiar first plumage of their own, as with the robin.
IV. When the adult male resembles the adult female, the young of both
sexes in their first plumage resemble the adults, as with the
kingfisher, many parrots, crows, hedge-warblers.
V. When the adults of both sexes have a distinct winter and summer
plumage, whether or not the male differs from the female, the young
resemble the adults of both sexes in their winter dress, or much more
rarely in their summer dress, or they resemble the females alone. Or
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