VALIDITY Of SOME FORMS Of MIMICRY. 71 1 



necessarily negative, and we must therefore try to find some 

 reasonable standard by which we can judge whether a particular 

 bird is a butterfly eater or not. We shall not be far wrong if we 

 employ the criteria accepted by Mr. Guy Marshall in his paper 

 " Birds as a factor in the production of Mimetic Resemblances 

 among Butterflies" (Trans. Ent. Soc. Lond. 1909), only in this 

 case in a contrary sense. Speaking of the want of real evidence 

 on the part of the Anti-Mimici'ists, he says: — " When a naturalist 

 who has spent some time in the tropics expresses a decided 

 opinion to the eft'ect that birds do not normally eat butterflies, 

 because he has never observed them doing so, it is incumbent on 

 us, befoi'e accepting his evidence as having any i-eal scientific 

 A^alue, to satisfy ourselves that he has made a systematic and 

 thorough investigation of the subject, and that his views are not 

 based merely on casual and inadequate observations. For in a 

 matter of this kind there is giuve danger that absence of evidence 

 may be due simply to lack of observation. If a collector main- 

 tains that birds do not eat butterflies, we are justified in asking 

 him for a fall list (italics mine) of the other insects which he has 

 seen captured by birds. And I venture to think that a closer 

 inquiry of this kind would reveal the fact that most of the 

 negative evidence which has been brought up against the Select- 

 ionist interpretation of mimicry is really of little worth." 



Passing over the obvious reply that as it was the Selectionists 

 who first asserted that birds ate butterflies, it is their duty to 

 prove it if they wish their theory accepted, it would appear 

 tha,t Mr. Marshall does not consider it necessary for an observer 

 to be very accurate as to the species captured before attributing 

 butterfly-catching propensities to certain birds. 



In the case of the Redstart we read that " They take flies, gnats, 

 small butterflies, and all sorts of small two- and four- winged insects, 

 partly on the wing and partly at rest" ; and again, "It feeds on 

 flies, gnats, small butterflies, and vai'ious other kinds of small 

 coleopterous and other insects, caterpillars, etc." Now if such 

 evidence is accepted, namely, that the Redstart eats butterflies, 

 without the necessity of naming the individual species captured 

 (though it might well be suggested that these small butterflies 

 were really small moths), it would appear only just that when 

 such an authority as Legge states that the food of the large Indian 

 Cuckoo-Shrike consists of " caterpillars, grasshoppers and various 

 other kinds of coleopterous insects " without mention of butterflies, 

 that such should be regarded as sufiicient evidence that butterflies 

 are not destroyed by it in sufficient numbers to cause any form of 

 mimicry. But, on the other hand, when we I'ead of a bird feeding 

 " on beetles and the many larger members of the insect kingdom 

 which aflfect Ceylon forests," it is quite possible that such a one 

 would produce a struggle for existence among butterflies. It is 

 only by adopting some such standard as this, faulty though it may 

 be, that we are likely to come to any conclusion. As to the actual 

 observation of insects captured by birds, no one who has not 



