494 THE CUCKOO 



take the pied-wagtail as typical) there is almost invariably a great 

 resemblance between the eggs of the cuckoo and the fosterer. There 

 is also a third class in which resemblance undoubtedly exists in some 

 cases, while in others it is equally certainly lacking. The tree-pipit 

 and robin may be quoted as belonging to this category. On the 

 Continent, eggs of the cuckoo found in nests of the redstart and 

 brambling almost invariably resemble those of the fosterer very 

 closely. Dr. Rey states that out of 67 cuckoos' eggs taken from 

 redstarts' nests, no fewer than 57 were blue, and, except in size, did 

 not differ from those of the redstart, while the few examples obtained 

 from bramblings' nests in all cases showed close mimicry. Other 

 species in which mimicry commonly exists are the common white- 

 throat, the garden-warbler, the reed-warbler, and the sedge-warbler ; 

 while, on the other hand, no authenticated instance of mimicry has 

 been recorded in the case of the common wren, willow-wren and 

 its congeners, and only very rarely in the case of the hedge-sparrow. 1 

 On the whole, it may confidently be stated that successful mimicry 

 exists only in a minority of cases, and is less prevalent in the British 

 Isles than on the Continent, while in India some wonderful types of 

 erythristic eggs have been obtained which are unknown in Europe. 



One other point about the egg of the cuckoo deserves a word of 

 mention. Not only is there considerable range of colouring in these 

 eggs, but the size is also variable, and in certain cases the egg of the 

 cuckoo bears some relation to the size of the eggs of its host. Thus 

 Mr. R H. Read informs me that the largest cuckoo's egg he ever 

 found was in the nest of the largest host, a song- thrush, while the 

 smallest was with the smallest eggs of any represented host, namely 

 the sedge-warbler. Mr. O. H. Latter has investigated the subject 

 from a mathematical standpoint in Siotnetrika, i. pt. ii. pp. 164-76, 

 and iv. pp. 363-73, and comes to the conclusion that eggs found 

 in nests of hedge-sparrow, tree-pipit, meadow-pipit, and robin vary 



' Cf. N. P. Ticehurst, Birds of Kent, p. 247 ; W. Borrer, Birds of Sussex, p. 167 ; S. Lewis, 

 Zoologist, 1906, p. 34. 



