208 Major R. F. Meiklejolin on the [Ibis, 



Now if we refer to the facts we possess regarding the 

 coloration of Cuckoos' eggs (pp. 198-200), we find that tlie 

 first of these suppositions is confirmed by (b) and the third 

 by (c), and the fact that Cuckoos' eggs of this type are 

 seldom met with. The preference of parasitic species for 

 "domed" nests has been called attention to in reference 

 to the Cow-birds, and when other nests with suitably 

 coloured eggs were not available, the tendency might be 

 to us€ "domed" ones. Our second supposition is supported 

 by general experience, and the only two facts that present 

 any difficulty are {d) and (^). 



The latter^ however, is not difficult to fit in, since although 

 the Redstart nests in holes, it is evident that when the 

 female Cuckoo can insert her egg she can also see the 

 colour of the others. Fact (d) is certainly curious, though 

 Dr. Rey's statement, referred to previously, that eggs of the 

 Hedge-Sparrow type do not occur is hardly correct, since 

 those of the Redstart type, which are virtually the same, 

 certainly do. Yet the fact remains that the Hedge-Sparrow 

 is a common foster-parent, but eggs found in the nests of 

 this species seem never blue ! Possibly this may be due 

 to the fact that this bird is very common ; its nests are 

 not usually well concealed and may be found practically 

 throughout the nesting-season. The Cuckoo may know by 

 instinct that the H edge-Sparrow will accept eggs of any 

 colour, and consequently uses it as a "makeshift" when 

 other suitable nests are not available. 



This explanation, it must be admitted, is unsatisfactory, 

 and undoubtedly this particular evidence seems to point to 

 the conclusion that it is the foster-parents or the nest, and 

 not the colour of the eggs, that influences the Cuckoo in 

 her choice ; yet such a theory is more difficult to fit in with 

 our other facts. 



And moreover, if the theory regarding the connec- 

 tion between food and egg-coloration were correct, blue 

 Cuckoos' eggs w^ould be common in Britain, and this is 

 not so ! 



I have, on occasions, experimented in localities where the 



