1918-] by Birds of Eggs unlike their oivn. 135 



It is interesting here to recall Mr. Stuart Baker's con- 

 viction, arrived at as the result of the study of " very many 

 hundreds " of eggs of Asiatic Cuckoos (including over a 

 thousand of C. bakeri alone), that .... 



" 2. The majority of foster-parents are totally unconscious 

 of incongruity in size between their own eggs and 

 that of the Cuckoo. 



"3. That they are not conscious of variation in shape." 

 ('Ibis/ 1913, p. 386.) 



For "totally unconscious" I would substitute ''rela- 

 tively unsuspicious " ; yet I cannot help recalling the great 

 disparity in size that sometimes in butterflies exists between 

 model and mimic, and also various incidents in my insect 

 experiments which showed that a bird may be far more 

 strongly impressed by a very small diflference in coloration 

 than by a very large difference in size. My prettiest 

 examples were obtained from a Milanji Bulbul [Phylla- 

 strephus niilanjensis). Char axes ethalion is a butterfly with 

 black non-mimetic males and many female forms, each 

 of which is a beautiful mimic of one or other of the larger 

 species of Charaxes that are protected by their size and 

 power. Yet the Milanji Bulbul, so far from realizing 

 that it was size that was at the bottom of her trouble 

 with the larger species, always, after an unpleasant 

 experience with these, refused to touch the small mimetic 

 individuals also, though she readily attacked their differ- 

 ently-coloured males. 



10. Sight, not smell, was the means of 1'ecognition. — In 

 every case in which the coloration of the eggs was the 

 same the substitute was accepted, even by birds that 

 freely rejected eggs of the wrong colour : this even where 

 the eggs belonged to different families and differed in taste 

 (as I ascertained) and therefore, presumably, in smell (which 

 I could not sufiiciently appreciate). In my very numerous 

 experiments in regard to the preferences of insectivorous 

 birds the evidence was all against the view that smell is 

 used by them to an appreciable extent for purposes of 

 recognition (though it is true that discomfort was shown 



