Ch. XVI. the young like adults of same sex. 219 
and sex ; but it would not be worth while to attempt to 
follow out these complex relations. 
Class YI. The young in their first 'plumage differ 
from each other according to sex ; the young males 
resembling more or less closely the adult males, and the 
young females more or less closely the adult females . — 
'Hie cases in the present class, though occurring in 
various groups, are not numerous; yet, if experience 
had not taught us to the contrary, it seems the most 
natural thing that the young should at first always 
resemble to a certain extent, and gradually become 
more and more like, the adults of the same sex. 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; the male blackbird (Turdus 
merula) can be distinguished in the nest from the female, 
as the main wdng-feathers, which are not moulted so 
soon as the body-feathers, retain a brownish tint until the 
second general moult.^^ The two sexes of the mock- 
ing bird (Turdus 'polyglottus, Linn.) differ very little 
from each other, yet the males can easily be distin- 
guished at a very early age from the females by shew- 
ing more pure white.^^ The males of a forest-thrush 
and of a rock-thrush (viz. 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 wdng and tail- 
feathers edged with blue, whilst those of the female are 
Blytb, in Cliarlesworth’s ‘Mag. of Nat. Hist.’ vol. i. 1837, p. 362 ; 
and from information given to me by him. 
Andiibon, ‘ Ornith. Biography,’ vol. i. p. 113. 
