Dhaf XVI. Birds— -Conspiawus Colours. 491 



be forgotten, in which it was shewn that the best sorigstors are 

 rarely ornamented with bright tints. It would appear that female 

 birds, as a general rule, have selected their mates either for their 

 sweet voices or gay colours, but not for both charms combined. 

 Some spec'es, which are manifestly coloured for the sake of 

 protection, such as the jack-snipe, woodcock, and night-jar, are 

 likewise marked and shaded, according to our standard of taste, 

 with extreme elegance. In such cases we may conclude that 

 both natural and sexual selection have acted conjointly for 

 protection and ornament. "Whether any bird exists which does 

 not possess some special attraction, by which to charm the 

 opposite sex, maybe doubted. When both sexes ai'e so obscurely 

 coloured that it would be rash to assume the agency of sexual 

 selection, and when no direct evidence can bu advanced shewing 

 that such colours serve as a protection, it is best to own complete 

 ignorance of the cause, or, which comes to nearly the same thing, 

 to attribute the result to the dirt-ct action of the conditions of life. 

 Both sexes of many birds are conspicuously, though not 

 brilliantly coloured, such as the numerous black, white, or 

 piebald species; and these colours are probably the result of 

 sexual selection. With the common blackbird, capercailzie, 

 blackcock, black scoter-duck (Oidemia), and even with one of 

 the bii'ds of pai-adise (^Lophorina idra), the males alone are black, 

 whilst the females are brown or mottled ; and there can hardly 

 be a doubt that blackness in these cases has been a sexually 

 selected character. Therefore it is in some degree probable that 

 the complete or partial blackness of both sexes in such birds as 

 crows, certain cockatoos, storks, and swans, and many murine 

 birds, is likewise the result of sexual selection, accompanied by 

 equal transmission to both sexes ; for blackness can hardly serve 

 iu any case as a protection. With several birds, in which the 

 male alone is tilaift, and in others in which both sexes are 

 black, thereat ofreteiabout the head is brightly coloured, and 

 the contrast thus afforded adds much to their beauty ; we see 

 this in the bright yellow beak of the male blackbird, in the 

 crimson skin over the eyes of the black-cook and capercailzie, in 

 the brightly and variously coloured beak of the scoter-drake 

 (Oidemia), in the red beak of the chough {Corvus yraculus, Linn.), 

 of the black swan, and the black stork. This leads me to remark 

 that it is not incredible that toucans may owe the enormous 

 size of their beaks to sexual selection, for the sake of displaying 

 the diversified and vivid stripes of colour, with which these 

 organs are ornamented.^' The naked skin, also, at the base of the 



" No satisfactory explanation has size, and still less of the bright 

 ?ver been offi-roil "f tlie immense colours, rf the toucan's beak. Jir 



