not numerous; yet it seems the most natural thing that the young should
at first somewhat resemble the adults of the same sex, and gradually
become more and more like them. The adult male blackcap (Sylvia
atricapilla) has a black head, that of the female being reddish-brown;
and I am informed by Mr. Blyth, that the young of both sexes can be
distinguished by this character even as nestlings. In the family of
thrushes an unusual number of similar cases have been noticed; thus,
the male blackbird (Turdus merula) can be distinguished in the nest
from the female. The two sexes of the mocking bird (Turdus polyglottus,
Linn.) differ very little from each other, yet the males can easily be
distinguished at a very early age from the females by showing more pure
white. (46. Audubon, Ornith. Biography, vol. i. p. 113.) The males of
a forest-thrush and of a rock-thrush (Orocetes erythrogastra and
Petrocincla cyanea) have much of their plumage of a fine blue, whilst
the females are brown; and the nestling males of both species have
their main wing and tail-feathers edged with blue whilst those of the
female are edged with brown. (47. Mr. C.A. Wright, in Ibis, vol. vi.
1864, p. 65. Jerdon, Birds of India, vol. i. p. 515. See also on the
blackbird, Blyth in Charlesworth s Magazine of Natural History, vol.
i. 1837, p. 113.) In the young blackbird the wing-feathers assume their
mature character and become black after the others; on the other hand,
in the two species just named the wing-feathers become blue before the
others. The most probable view with reference to the cases in the
present class is that the males, differently from what occurs in Class
I., have transmitted their colours to their male offspring at an
earlier age than that at which they were first acquired; for, if the
males had varied whilst quite young, their characters would probably
have been transmitted to both sexes. (48. The following additional
cases may be mentioned; the young males of Tanagra rubra can be
distinguished from the young females (Audubon, Ornith. Biography,
vol. iv. p. 392), and so it is within the nestlings of a blue nuthatch,
Dendrophila frontalis of India (Jerdon, Birds of India, vol. i. p.
389). Mr. Blyth also informs me that the sexes of the stonechat,
Saxicola rubicola, are distinguishable at a very early age. Mr. Salvin
gives ( Proc. Zoolog. Soc. 1870, p. 206) the case of a humming-bird,
like the following one of Eustephanus.)
In Aithurus polytmus, a humming-bird, the male is splendidly coloured
black and green, and two of the tail-feathers are immensely lengthened;
the female has an ordinary tail and inconspicuous colours; now the
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