INDIAN FLY-CATCHERS 183 



that there is something in their constitution that pre- 

 vents green variations appearing in their plumage. 



In conclusion, note must be made of the fact that 

 fly-catchers, although they subsist almost entirely 

 upon insect diet, appear but rarely to devour butter- 

 flies. I have watched fly-catchers closely for several 

 years, and have on two occasions only seen them chase 

 butterflies or moths. Five years ago in Madras I ob- 

 served a paradise fly-catcher chasing a small butterfly, 

 and recently, in the Himalayas, I saw a grey-headed 

 fly-catcher drop down from a tree and seize a moth 

 that was resting in the gutter. The reason why fly- 

 catchers do not often attack butterflies is obvious ; 

 these insects offer very little meat and a great deal of 

 indigestible wing surface. Nevertheless, the theory 

 of protective mimicry is almost exclusively illustrated 

 by examples taken from butterflies. In theory, these 

 creatures are so relentlessly persecuted by insectivorous 

 birds that in order to escape their foes many edible 

 butterflies mimic the appearance of unpalatable species. 

 Unfortunately for theory, few creatures in practice 

 seem to attack butterflies when on the wing, which is 

 just the time when the " mimicry " is most obvious. 



The elegant httle fly-catchers, then, are birds which 

 mock Darwin, laugh at Wallace, and make merry at 

 the expense of Muller and Bates ! 



