Eyesight of Birds 



It would therefore seem that all these elaborate 

 " protective " devices are unnecessary refinements 

 if regarded as a protection against invertebrate, 

 reptilian, and amphibian foes. Birds, on the other 

 hand, appear to have exceedingly sharp eyesight, 

 so that in order to deceive them the resemblance 

 requires to be very close. Indeed, as regards 

 those birds which systematically hunt for their 

 prey among leaves and grass, it seems doubtful 

 whether the alleged "protective" resemblances of 

 caterpillars to twigs, etc. , are sufficient to be of much 

 use to them. Thus Beddard writes (on page 91 

 of Animal Colouration) : " Judging of birds by 

 our own standard which is the way in which 

 nearly all the problems relating to colour have 

 been approached does it seem likely that we 

 should fail to see a caterpillar, perhaps as long 

 or longer than the arm, of an obviously different 

 texture from the branches, and displaying in 

 many cases through its semi-transparent skin the 

 pulsation of the heart, for which we were par- 

 ticularly searching?" 



Now, birds certainly feed very largely on 

 caterpillars, while they are but rarely seen to eat 

 butterflies. If, therefore, the aim and object of 

 these special resemblances is the protection of 

 the species, we should expect to see them in a 

 nearly perfect state in caterpillars on which 

 birds feed very largely, and poorly developed in 

 butterflies, which do not appear to be greatly 



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