young males, instead of resembling the adult female, in accordance with
the common rule, begin from the first to assume the colours proper to
their sex, and their tail-feathers soon become elongated. I owe this
information to Mr. Gould, who has given me the following more striking
and as yet unpublished case. Two humming-birds belonging to the genus
Eustephanus, both beautifully coloured, inhabit the small island of
Juan Fernandez, and have always been ranked as specifically distinct.
But it has lately been ascertained that the one which is of a rich
chestnut-brown colour with a golden-red head, is the male, whilst the
other which is elegantly variegated with green and white with a
metallic green head is the female. Now the young from the first
somewhat resemble the adults of the corresponding sex, the resemblance
gradually becoming more and more complete.
In considering this last case, if as before we take the plumage of the
young as our guide, it would appear that both sexes have been rendered
beautiful independently; and not that one sex has partially transferred
its beauty to the other. The male apparently has acquired his bright
colours through sexual selection in the same manner as, for instance,
the peacock or pheasant in our first class of cases; and the female in
the same manner as the female Rhynchaea or Turnix in our second class
of cases. But there is much difficulty in understanding how this could
have been effected at the same time with the two sexes of the same
species. Mr. Salvin states, as we have seen in the eighth chapter, that
with certain humming-birds the males greatly exceed the females in
number, whilst with other species inhabiting the same country the
females greatly exceed the males. If, then, we might assume that during
some former lengthened period the males of the Juan Fernandez species
had greatly exceeded the females in number, but that during another
lengthened period the females had far exceeded the males, we could
understand how the males at one time, and the females at another, might
have been rendered beautiful by the selection of the brighter coloured
individuals of either sex; both sexes transmitting their characters to
their young at a rather earlier age than usual. Whether this is the
true explanation I will not pretend to say; but the case is too
remarkable to be passed over without notice.
We have now seen in all six classes, that an intimate relation exists
between the plumage of the young and the adults, either of one sex or
both. These relations are fairly well explained on the principle that
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