82 A YOUNG CUCKOO 



Examples 2/8, 30, 69, and 70 supply ten instances 

 of blue eggs to which the respective Cuckoo's eggs 

 show not the remotest resemblance. Blue eggs of 

 the Cuckoo are held to be rare ; but, that they should 

 occur is not surprising, seeing that the Yellow-billed, 

 Black-billed and other Cuckoos lay plain blue eggs, and 

 the Great Spotted Cuckoo an egg greenish-blue in 

 the ground. On the contrary, if it be accepted that 

 the Cuckoo can and does, even rarely, lay a 

 blue egg, one might reasonably have expected that, 

 however severely, upon the theory of discrimination, 

 such eggs might be dealt with by foster-species 

 laying eggs of a different type, some of these blue 

 eggs would fall to the share of our fairly numerous 

 layers of blue eggs, who, to judge by the fact that 

 they do not discriminate against the utterly dissimilar 

 mottled eggs now foisted upon them, might have 

 been trusted to hatch eggs that were not dissimilar, 

 thus preserving to us the strain of Cuckoos laying 

 blue eggs. 



Blue eggs are said to be laid by the Cuckoo more 

 frequently on the Continent than in the British 

 Isles. It is remarkable that the tendency to produce 

 such a variety should on the Continent be matched 

 by a corresponding discrimination on the part of the 

 Redstart, in whose nest it is said at times to be 

 placed, whilst in the British Isles inability in the 

 Cuckoo to supply such a variety of egg should find 

 our Redstarts equally unable to discriminate against 

 the monstrous make-shifts here foisted upon them. 

 Witness Example 8. 



I should, perhaps, add that the "explanatory 

 hypothesis " put forward by Professor Newton 



