SEXUAL SELECTION 547 



in the coloring of the tail — "some having the whole of the 

 feathers blue, while others have the eight central ones tipped 

 with beautiful green." It does not appear that intermediate 

 gradations have been observed in this or the following cases. 

 In the males alone of one of the Australian paroquets "the 

 thighs in some are scarlet, in others grass green." In an- 

 other paroquet of the same country "some individuals have 

 the band across the wing-coverts bright yellow, while in 

 others the same part is tinged with red." " In the United 

 States some few of the males of the Scarlet Tanager {Tana- 

 gra rubra) have "a beautiful transverse band of glowing red 

 on the smaller wing-coverts;" " but this variation seems to 

 be somewhat rare, so that its preservation through sexual 

 selection would follow only under unusually favorable cir- 

 cumstances. In Bengal the Honey buzzard {Pernis cristata) 

 has either a small rudimental crest on its head, or none at 

 all; so slight a difference, however, would not have been 

 worth notice, had not this same species possessed in South- 

 ern India "a well-marked occipital crest, formed of several 

 graduated feathers." " 



The following case is in some respects more interesting. 

 A pied variety of the raven, with the head, breast, abdomen, 

 and parts of the wings and tail-feathers white, is confined to 

 the Feroe Islands. It is not very rare there, for Grraba saw 

 during his visit from eight to ten living specimens. Al- 

 though the characters of this variety are not quite constant, 

 yet it has been named by several distinguished ornitholo- 

 gists as a distinct species. The fact of the pied birds being 

 pursued and persecuted with much clamor by the other ra- 

 vens of the island was the chief cause which led Briinaich 

 to conclude that they were specifically distinct; but this is 

 now known to be an error." This case seems analogous 



8' Gould, "Handbook to Birds of Australia," vol. ii. pp. 32 and 38. 



88 Audubon, "Ornitholog. Biography," 1838, vol. iv. p. 889. 



5' Jerdon, "Birds of India," vol. i. p. 108; and Mr. Blyth, in "Land and 

 Water," 1868, p. 381. 



«> Graba, "Tagebuch, Eeise nach Faro," 1830, s. 51-54. Macgillivray, 

 "Hiat. British Birds," voL iu. p. 745. "Ibis," vol. v., 1863, p. 469. 



