Chap. XYL 
CONSPICUOUS COLOUKS. 
229 
the first year, and of the adults during the winter, are 
either pure white, or much paler-coloured than during 
the breeding-season. These latter cases offer another 
instance of the capricious manner in which sexual se- 
lection appears often to have acted.^^ 
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 
escape 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 
protection. 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 perfectly white, or intensely black; so that 
these colours may possibly 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 carcase 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 coloured 
individuals. Hence conspicuous colours cannot have 
been gradually acquired for this purpose through na- 
tural selection.^^ 
On Larns, Gavia, and Sterna, see Macgillivray, ‘ Hist. Brit. Birds, ’ 
vol. V. p. 515, 584, 626. On the Anser hyperboreus, Andubon, ‘ Ornith. 
Biography,’ vol. iv. p. 562. On the Anastomus, Mr. Blyth, in ‘ Ibis,’ 
1867, p. 173. 
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 
