Chap. XVI. Birds — Young like Adult Females. 467 



such cases ought to come under the present, or under the third 

 or fourth classes. So again the young of the two sexes, instead of 

 being quite alike, may differ in a slight degree from each other, 

 as in our sixth class. These transitional cases, however, are 

 few, or at least are not strongly pronounced, in comparison with 

 those which come strictly under the present class. 



The force of the present law is well shewn in those groups, 

 in which, as a general rule, the two sexes and the young are all 

 alike ; for when in these groups the male does differ from the 

 female, as with certain parrots, kingfishers, pigeons, &c, the 

 young of both sexes resemble the adult female. 2 We see the 

 same fact exhibited still more clearly in certain anomalous cases ; 

 thus the male of Hdiothrix auriculata (one of the humming- 

 birds) differs conspicuously from the female in having a splendid 

 gorget and fine ear-tufts, but the female is remarkable from 

 having a much longer tail than that of the male ; now the young 

 of both sexes resemble (with the exception of the breast being 

 spotted with bronze) the adult female in all other respects, 

 including the length of her tail, so that the tail of the male 

 actually becomes shorter as he reaches maturity, which is a most 

 unusual circumstance. 3 Again, the plumage of the male goos- 

 ander (Meigus merganser) is more conspicuously coloured than 

 that of the female, with the scapular and secondary wing-feathers 

 much longer ; but differently from what occurs, as far as I know, 

 in any other bird, the crest of the adult male, though broader 

 than that of the female, is considerably shorter, being only a 

 little above an inch in length ; the crest of the female being two 

 and a half inches long. Now the young of both sexes entirely 

 resemble the adult female, so that their crests are actually of 

 greater length, though narrower, than in the adult male. 4 



When the young and the females closely resemble each other 

 and both differ from the males, the most obvious conclusion is 



2 See, for instance, Mr. Gould's and of the King Lory, with which 



account (' Handbook to the Birds of the same rule prevails. Also Jerdon 



Australia,' vol. i. p. 133) of Cyanal- ('Birds of India,' vol. i. p. 2G0) on 



cyon (one of the Kingfishers) in the Paleeornis rosa, in which the 



which, however, the young male, young are more like the female than 



thouo-h resembling; the adult female, the male. -.See Audubon (' Ornith. 



is less brilliantly coloured. In some Biograph. vol. ii. p. 475) on the 



species of Dacelo the males have two sexes and the young of Columba 



blue tails, and the females brown passerina. 



anes; and Mr. R. B. Sharpe informs 3 I owe this information to Mr. 



tne that the tail of the young male Gould, who shewed me the spec ; - 



of D. gaudichaudi is at first brown. mens ; see also his ' Introduction tc 



Mr. Gould has described (ibid. vol. the Trochilidae/ 1861, p. 120. 



ii. pp. 14, 20, 37) the sexes and the 4 Macgillivray, 'Hist. Brit. Birds, 



young of certain black Cockatoos vol. v. pp. 207-214. 



