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ADAPTIVE COLORATION 207 



'That therefore on the whole, the theory of Wallace and Bates is 

 supported by the facts detailed in this and my former papers, so far as 

 they deal with birds (and with the one mammal used). Professor 

 Poulton's suggestion that animals may be forced by hunger to eat un- 

 palatable forms is also more than confirmed, as the unpalatable forms 

 were commonly eaten without the stimulus of actual hunger generally, 

 also, I may add, without signs of dislike. " 



Though insects have many vertebrate and arthropod enemies, it is 

 probable that the evolution of mimetic resemblance, implying warning 

 coloration, has been brought about chiefly by insectivorous birds. 



Neglecting papers of minor importance, we may pass at once to the 

 most important contribution upon this subject the voluminous work 

 of Marshall and Poulton upon mimicry and warning colors in South 

 African insects. These investigators have found that birds are to be 

 counted as the principal enemies of butterflies; that the Danainae and 

 Acraeinae, which are noted as models, are particularly immune from de- 

 struction, while unprotected forms suffer; and that mimicking, though 

 palatable, species share the freedom of their models. The same is true 

 of beetles, of which Coccinellidae, Malacodermidse (notably Lycus) 

 Cantharidse and many Chrysomelidae serve as models for many other 

 Coleoptera, being "conspicuous and constantly refused by insect- 

 eaters." In short, the splendid work of Marshall and Poulton tends to 

 place the theory of Batesian and Miillerian mimicry upon a substantial 

 foundation of observational and experimental evidence. 



In regard to the important question do birds avoid unpalatable 

 insects instinctively or only as the result of experience the evidence is 

 all one way. Several investigators, including Lloyd Morgan, have 

 found that newly-hatched birds have no instinctive aversions as regards 

 food, but test everything, and (except for some little parental guidance) 

 are obliged to learn for themselves what is good to eat and what is not. 

 This experimental evidence that the discrimination of food by birds is 

 due solely to experience, was evidently highly necessary to place the 

 theory of mimicry especially the Miillerian theory upon a sound 

 basis. 



Though butterflies as a group are much subject to the attacks of 

 birds in the tropics, it has been asserted that butterflies in temperate 

 regions are as a whole almost exempt from the attacks of birds, and that 

 consequently the mimicry of the monarch (Fig. 247) by the viceroy is 

 of no advantage. In answer to this assertion Marshall has published a 

 long list of references showing that butterflies are attacked by birds 



