SEXUAL SELECTION 635 



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 color with which these organs are orna- 

 mented." The naked skin, also, at the base of the beak 

 and round the eyes is likewise often brilliantly colored; and 

 Mr. Gould, in speaking of one species," says that the colors 

 of the beak "are doubtless in the finest and most brilliant 

 state during the time of pairing.*' There is no greater 

 improbability that toucans should be encumbered with 

 inunense beaks, though rendered as light as possible by 

 their cancellated structure, for the display of fine colors 

 (an object falsely appearing to us unimportant), than that 

 the male Argus pheasant and some other birds should be 

 encumbered with plum'es so long as to impede their flight. 

 In the same manner as the males alone of various species 

 are black, the females being dull colored, so in a few cases 

 the males alone are either wholly or partially white, as with 

 the several bell-birds of South America (Chasmorhynchus), 

 the Antarctic goose (^Bernicla antarctica), the silver-pheasant, 

 etc., while the females are brown or obscurely mottled. 

 Therefore, on the same principle as before, it is probable 

 that both sexes of many birds, such as white cockatoos, 

 several egrets with their beautiful plumes, certain ibises, 

 gulls, terns, etc., have acquired their more or less com- 

 pletely white plumage through sexual selection. In some 

 of these cases the plumage becomes white only at maturity. 



" No satisfactory explanation has ever been offered of the immense size, 

 and stUl less of the bright colors, of the toucan's beak. Mr. Bates ("The 

 Naturalist on the Amazons," vol. ii., 1863, p. 341) states that they use their 

 beaks for reaching fruit at the extreme tips of the branches ; and likewise, as 

 stated by other authors, for extraotiag eggs and young birds from the nests of 

 other birds. But, as Mr. Bates admits, the beak "can scarcely be considered 

 a very perfectly formed instrument for the end to which it is applied." The 

 great bulk of the beak, as shown by its breadth, depth, as well as length, is 

 not intelligible on the view that it serves merely as an organ of prehension. 

 Mr. Belt believes ("The Naturalist in Nicaragua," p. 197) that the principal 

 use of the beak is as a defence against enemies, especially to the female while 

 nesting in a hole in a tree. 



" Bamphastos oarinatus, Gould's "Monograph of Ramphastidse. " 



