146 SEXUAL SELECTION: BIRDS. [Paet IL 



so as to have aqcuired white tips ? The variations may 

 have been gradual, or somewhat abrupt as in the case re- 

 cently given of the humming-birds near Bogota, in which 

 certain individuals alone have the "central tail-feathers 

 tipped with beautiful green." In the female of the Uros- 

 ticte I noticed extremely minute or rudimental white tips 

 to the two outer of the four central black tail-feathers ; so 

 that here we have an indication of change of some kind in 

 the plumage of this species. If we grant the possibility 

 of the central tail-feathers of the male varying in white- 

 ness, there is nothing strange in such variations having 

 been sexually selected. The white tips, together with 

 the small white ear-tufts, certainly add, as the Duke of 

 Argyll admits, to the beauty of the male ; and whiteness 

 is apparently appreciated by other birds, as may be in- 

 ferred from such cases as the snow-white male of the ^ell- 

 bird. The statement made by Sir R. Heron should not 

 be forgotten, namely, that his peahens, when debarred 

 from access to the pied peacock, would not unite with any 

 other male, and during that season produced no offspring. 

 Nor is it strange that variations in the tail-feathers of the 

 Urosticte should have been specially selected for the sake 

 of ornament, for the next succeeding genus in the family 

 takes its name of Metallura from the splendor of these 

 feathers. Mr. Gould, after describing the peculiar plu- 

 mage of the Urosticte, adds, " that ornament and variety 

 is the sole object, I have myself but little doubt." 50 If this 

 be admitted, we can perceive that the males which were 

 decked in the most elegant and novel manner would have 

 gained an advantage, not in the ordinary struggle for life, 

 but in rivalry with other males, and would consequently 

 have left a larger number of offspring to inherit their 

 newly-acquired beauty. 



60 ' Intioduction to the TrochilidgD' 1861, p. 110. 





