The Brain-fever Bird 



operate on it. It is therefore absurd to look upon 

 natural selection as the direct cause of the origin 

 of the likeness. When once a certain degree of 

 resemblance has risen, it is quite likely that in 

 some cases natural selection has strengthened 

 the likeness. 



The second great objection to the Neo- 

 Darwinian explanation of the phenomenon 

 known as mimicry is that in many cases the 

 resemblance is unnecessarily exact. Even as 

 we saw how the Kallimas, or dead-leaf butter- 

 flies, carried their resemblance to dead leaves 

 to such an extent as to make it appear probable 

 that factors other than natural selection have had 

 a share in its production, so do we see in certain 

 cases of mimetic resemblance an unnecessarily 

 faithful likeness. 



The common Hawk Cuckoo of India (Hiero- 

 coccyx varius) furnishes an example of this : 

 " The brain-fever bird," writes Finn, on page 58 

 of Ornithological and Other Oddities, " is the 

 most wonderful feather copy of the Indian 

 Sparrow-hawk or Shikra (Astur badius). All the 

 markings in the hawk are reproduced in the 

 cuckoo, which is also of about the same size, and 

 of similar proportions in the matter of tail and 

 wing ; and both hawk and cuckoo having a first 

 plumage quite different from the one they assume 

 when adult, the resemblance extends to that too. 

 Moreover, their flight is so much the same that 



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