The " Colour-Blind Variety.'' 39 



scale — from birds that eject the cuckoo's egg and 

 either turn it out " or build it over," or desert the 

 nest, down to those who seem colour-blind and un- 

 suspicious, with all possible degrees of suspicion or 

 innocence between. 



Observation shows that eggs of the cuckoo de- 

 posited in nests of the red-backed shrike (Lauiiis 

 collurio), of the bunting (Eiiiberiza miliaria), and of 

 the icterine warbler approximate in their colouring 

 to eggs of these species — species in whose nests the 

 Cuckoo rarely, in comparison with others, deposits 



The facts according to the Eiicyclopcsdia Britannica 

 writer, up to a certain point at all events, square with 

 this theory. The birds in whose nests, in his view, 

 the cuckoo most commonly deposits eggs are of the 

 " colour-bhnd " variety, and more indifferent -to tam- 

 perings with the nest than are the red-backed shrike, 

 the bunting, and icterine warblers, where the cuckoo's 

 eggs approximate in their colouring to the eggs of 

 these species — species in whose nests the cuckoo more 

 rarely deposits eggs. 



Dr. Rey is here so far at one with Dr. Alfred 

 Newton, he says : " Each female lays only one egg in 

 one nest. If more than one be found they invariably 

 belong to different females." 



Most cuckoos, he holds again, " are in the habit of 

 placing their eggs in the nests of one species of bird, 

 and take to other nests only if they cannot find their 

 habitual nests." 



Mr. E. Hartert, at Mr. Bidwell's exhibition of 

 cuckoos' eggs, summarised as follows on this point 

 from Dr. Rey : 



