230 SEXUAL SELECTION I BIRDS. Paet II. 



As sexual selection depends on so fluctuating an 

 element as taste, we can understand how it is that with- 

 in the same group of birds, with habits of life nearly 

 the same, there should exist white or nearly white, 

 as well as black, or nearly black species, — for instance, 

 white and black cockatoos, storks, ibises, swans, terns, 

 and petrels. Piebald birds likewise sometimes occur 

 in the same groups, for instance, the black-necked 

 swan, certain terns, and the common magpie. That 

 a strong contrast in colour is agreeable to birds, we 

 may conclude, by looking through any large collection 

 of specimens or series of coloured plates, for the sexes 

 frequently differ from each other in the male having 

 the pale parts of a purer white, and the variously 

 coloured dark parts of still darker tints than in the 

 female. 



It would even appear that mere novelty, or change 

 for the sake of change, has sometimes acted like a 

 charm on female birds, in the same manner as changes 

 of fashion with us. The Duke of Argyll says,^^ — and I 

 am glad to have the unusual satisfaction of following 

 for even a short distance in his footsteps — " I am more 

 " and more convinced that variety, mere variety, must 

 " be admitted to be an object and an aim in Nature." 

 I wish the Duke had explained what he here means by 

 Nature. Is it meant that the Creator of the universe 

 ordained diversified results for His own satisfaction, or for 

 that of man ? The former notion seems to me as much 

 wanting in due reverence as the latter in probability. 

 Capriciousness of taste in the birds themselves appears 

 a more fitting explanation. For example ; the males 



many other species are black. This fact supports the conjecture that 

 these conspicuous colours may aid the sexes in finding each other during 

 the breeding-season. 



^6 ' The Journal of Travel/ edited by A. Murray, vol. i. 1868, p. 286. 



