Chap. XVf. Birds — Young like both Adults. 487 



Class VI. The, young in their first plumage differ from each ilhei 

 acenrding tn sex ; the y'lUng males resemhling more or less closely the aduli 

 males, and the young females more or less closely the adult females.— 

 The cases in the pveseut class, though occurrinj} in various groups, are 

 not nuiuerous ; yet it seems the most natural thing that the young 

 should at first soniewliat resemble the adults of the same sex, and 

 gradually become more and more like tliem. The adult male blackcap 

 {Sylvia atricapiUa) has a black head, that of the ftmale bting reddish- 

 brown ; and I am informed by Mr. Blyth, that the yuung of butli sexes 

 oau be distinguished by this character eveji as nestlings. In the family 

 of thrushes an unusual number of similar cases have been noticed ; thus, 

 the male blackbird (Jiurdus merulaj can be diotinguished in the nest 

 from the female. The two sexes of tlip mocking bird (Turdus polygluttus, 

 Linn.) differ very little from each other, yet the males can easily be 

 distinguished at a vi-ry eaily age from the females by sliening mure 

 pure white.*" Tlie males ot a forest-thrush and of a rock-thrush 

 {Orocctes vrythrogastra and Petrocincla eyanea) have much of their 

 plumage of a tine blue, whilst the females are brown ; an.l the nestling 

 males of botli species )iHve their main wing and tail-feathers edged witn 

 blue, whilst thuse of the female are edged with brown.*' In tlie young 

 bhiclibird the wing feathers assume tin ir mature chaiacter and become 

 black after tlie others ; on the otlier han I, iu the two species just named 

 the wing-feuthers become blue before tlie others. The most probable 

 view with reference to the cases iu the present class is that the males, 

 dilterently from what occurs in Class [., have transmitted their colours 

 to tlieii- male offspring at an earlier age than that at which they were 

 fir=t acquired ; for, if the males had varied whilst quite ycung, their 

 chaiacters would probably liave been transmilted to both sexes.*' 



In Aithurus polytmus, a humming-bird, the male is splendidly coloured 

 bl.ick iiml green, and two of the tail-feathers nre immensely lengthened ; 

 the female has an ordinary tail and inconspicuous colours; now the 

 young males, instead of resembling the adult female, in accordance 

 with the common rule, begin from the iii'st to assume the colcuis proper 

 to their sex, and their tail-feathers soon become elongated. I owe this 

 infoimation to Mr. Gould, who has given me the following more striking 

 anil as yet unpublished case. Tao humming-birds lielonging to the 

 genus Bustephauus, both beautifully coloured, inhabit the small island 

 of Juan Fernandez, and have always been ranked as specifically dis- 

 tinct. But it has lately been ascertained that the one, which is of a 

 rich chesnut brown colour with a golden-red head, is tlie mule, whilst 

 the other, which is elegantly variegated with green and white with a 

 metallic-green head is the female. Now the young Irum the llrst 



*» Audubon, ' Ornith. Biography,' ' Ornith. Biography,' vol. iv. p. 392), 



vol. i. p. 113. and so it is with the nestlings of a 



*' Mr. C. A, Wright, in 'Ibis,' hlae n\itha,tch, Bendrophila frontalis 



vol. vi. 1864, p. 65. Jerdon, ' Birds of India (Jerdon, ' Birds of India,' 



of India,' vol. i. p. 515. See also on vol. i. p. 389). Mr. Blyth also 



the blackbird, Blyth in Charles- informs me that the sexes of the 



worth's ' Mag. of Nat. History,' vol. stonechat, Saxicola rubicola, are 



i. 1837, p. 113. di.stinguishable at a very early age. 



*• The following additional cases Mr. Salvia gives (' Proc. Zoolog. Soc' 



may be mentioned ; the young males 1870, p. 206), the case of a hum- 



of ybmajro caij'a can be distinguished ming-bird, like the l'uUowiD(( one 7< 



I'lom the young females (Audubon, Eustephanus. 



