Chap. XVI.] CONSPICUOUS COLORS. 219 



breeding-season. These latter cases offer another instance 

 of the capricious manner in which sexual selection appears 

 often to have acted. 64 



The cause of aquatic birds having acquired a white 

 plumage so much more frequently than terrestrial birds, 

 probably depends on their large size and strong powers 

 of flight, so that they can easily defend themselves or es- 

 cape from birds of prey, to which, moreover, they are not 

 much exposed. Consequently sexual selection has not 

 here been interfered with or guided for the sake of pro- 

 tection. No doubt, with birds which roam over the open 

 ocean, the males and females could find each other much 

 more easily when made conspicuous either by being per- 

 fectly white, or intensely black ; so that these colors may 

 possible serve the same end as the call-notes of many land- 

 birds. A white or black bird, when it discovers and flies 

 down to a carcass floating on the sea or cast up on the 

 beach, will be seen from a great distance, and will guide 

 other birds of the same and of distinct species, to the 

 prey : but as this would be a disadvantage to the first 

 finders, the individuals which were the whitest or blackest 

 would not thus have procured more food than the less 

 strongly colored individuals. Hence conspicuous colors 

 cannot have been gradually acquired for this purpose 

 through natural selection. 55 



As sexual selection depends on so fluctuating an ele- 



64 On Larus, Gavia, and Sterna, see Macgillivray, 'Hist. Brit. Birds,' 

 vol. v. pp. 515, 584, 626. On the Anser hyperboreus, Audubon, 'Ornith. 

 Biography,' vol. iv. p. 562. On the Anastomus, Mr. Blyth, in ' Ibis,' 

 1867, p. 173. 



55 It may be noticed that with vultures, which roam far and wide 

 through the higher regions of the atmosphere, like marine birds over 

 the ocean, three or four species are almost wholly or largely white, and 

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

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

 the breeding-season. 



