210 SEXUAL SELECTION : BIRDS. [Part II. 



adults of the same sex. The adult male blackcap [Sylvia 

 atricapilld) 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 mam wing-feathers, which 

 are not moulted so soon as the body-feathers, retain a 

 brownish tint until the second general moult. 46 The two 

 sexes of the mocking-bird (Turdus polyglottus, Linn.) dif- 

 fer 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. 47 The males of a forest-thrush 

 and of a rock-thrush (viz., Orocetes erythrogastra and JPe- 

 trocincla cyaneci) have much of their plumage of a fine 

 blue, while the females are brown ; and the nestling males 

 of both species have their main wing and tail feathers 

 edged with blue, while those of the female are edged with 

 brown. 48 So that the very same feathers which in the 

 young blackbird assume their mature character and be- 

 come black after the others, in these two species assume 

 this character and become blue before the others. The 

 most probable view with reference to these cases is that 

 the males, differently from what occurs in Class L, have 

 transmitted their colors to their male offspring at an ear- 

 lier age than that at which they themselves first acquired 

 them; for if they had varied while quite young, they 

 would probably have transmitted all their characters to 

 their offspring of both sexes. 49 



46 Blyth, in Charlesworth's 'Mag. cf Nat. Hist.' vol. i. 1S37, p. 362; 

 and from information given to me by him. 



47 Audubon, 'Ornith. Biography,' vol. i. p. 113. 



48 Mr. C. A. Wright, in 'Ibis,' vol. vi. 1864, p. 65. Jerdon, 'Birds 

 of India,' vol. i. p. 515. 



4a The following additional cases may be mentioned : the young males 



