BIRDS— YOUNG LIKE BOTH ADULTS. 483 



had varied whilst quite young, their characters would probably 

 have been transmitted to both sexes." 



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

 colored black and green, and two of the tail-feathers are immense- 

 ly lengthened; the female has an ordinary tail and inconspicuous 

 colors; now the young males, instead of resembling the adult 

 female, in accordance with the common rule, begin from the first 

 to assume the colors 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 has given me the following more striking and as yet unpublished 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 colored, inhabit the small island of Juan Fernan- 

 dez, and have always been ranked as specifically distinct. But it 

 has lately been ascertained that the one, which Is of a rich chest- 

 nut brown color 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 re- 

 semblance 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 ap- 

 parently has acquired his bright colors 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 Rhynchasa 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 miglit 

 assume that during some former lengthened period the males ol 

 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 ren- 



** The following additional cases may be mentioned ; the young males 

 of Tanagra rubra can be distinguished from the young females (Au- 

 dubon, 'Ornith. Biography,' vol. iv. p. 392), and so it is with the nest- 

 lings 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, Saxioola 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. 



