126 
SEXUAL selection: birds. 
Part IL 
having the whole of the feathers blue, while others 
^^liave the eight central ones tipped with beautiful 
green.” It does not appear that intermediate gra- 
dations have been observed in this 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 
ruhra) 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 favourable circumstances. 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 gra- 
" duated 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 distinguished ornithologists as a distinct 
species. The fact of the pied birds being pursued and 
34 Gould, ‘ Handbook of Birds of Australia,’ vol. ii. p. 32 and 68. 
33 Audubon, ‘ Ornitbolog. Biography,’ 1838, vol. iv. p. 389. 
3^' Jerdon, ‘ Birds of India,’ vol. i. p. 108 ; and Mr. Blyth, in ‘ Land- 
and Water,’ 1868, p. 381. 
