206 BIRDS OF THE PLAINS 



declared, one ounce of good solid pugnacity is a better 

 weapon in the struggle for existence than many pounds 

 of protective colouration. 



Again, in the case of king-crows nigritude may be an 

 expression of vigour, the outward and visible sign of 

 strength. 



Let me make myself clear. Suppose that in a race of 

 savages those that had fair hair were stronger, bolder, 

 more prolific, and more pushing than the dark-haired 

 men. Fair hair, in some inexplicable way, always 

 accompanied strength and the like. It is obvious that, 

 under these conditions, the race would in time become 

 fair-haired : the milder dark men would eventually be 

 hustled out of existence. Fair hair would then be the 

 outward expression of vigour : it would not be the cause 

 of vigour, merely the accompaniment of it ; nor would 

 it be a direct product of natural selection. In the 

 same way it is possible that among drongos nigritude is 

 in some manner correlated with vigour. This idea is 

 not altogether fanciful. Are there not horses of " bad 

 colour " ? Are not white " socks " a sign of weakness ? 

 Is not roan a colour indicative of strength and en- 

 durance in a horse? 



May not the blackness and the forked tail of the 

 drongo cuckoo have arisen in the same way as they 

 arose in the king-crow ? In each case it may be an 

 accompaniment of vigour, or it may be the result of 

 sexual selection. Mrs. Surniculus may have had similar 

 tastes to Mrs. Dicrurus, and, since cuckoos seem 

 to be very plastic birds, her tastes have been grati- 

 fied. As another example of this plasticity I may cite 



