Chap. XIV.] VARIABILITY. 121 



or the following cases. In the males alone of one of the 

 Australian parrakeets " the thighs in some are scarlet, in 

 others grass-green." In another parrakeet 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 ( Tanagra 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 circum- 

 stances. 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 

 Southern India " a well-marked occipital crest formed of 

 several graduated feathers." ^* 



The following case is in some respects more interest- 

 ing : 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 Graba saw during his visit from eight to ten living 

 specimens. Although the characters of this variety are 

 not quite constant, yet it has been named by several dis- 

 tinguished ornithologists as a distinct species. The fact 

 of the pied birds being pursued and persecuted with 

 much clamor by the other ravens of the island was the 

 chief cause which led Brtinnich to conclude that it was 

 specifically distinct ; but this is now known to be an 

 error. ^' 



34 Gould, ' Hand-book of Birds of Australia,' vol. ii. pp. 32, 68. 



3^ Audubon, 'Ornitholog. BiograpLy,' 1838, vol. iv. p. 389. 



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

 and Water,' 1868, p. 381. 



3' Graba, 'Tagebuch, Reise nach Faro,' 1830, s. 51-54. Macgillivray 

 'Hist. British Birds,' vol. iii. p. 745. 'Ibis,' vol. v. 1863, p. 469. 



35 



