COLOURATION OF BIRDS AND THEIR EGGS. 173 



Moreover, I have a note to the effect that near Eyam, in 1887, 

 some Jackdaws were nesting among the branches, after the man- 

 ner of Books. In the * Naturalists' Journal' (vol. vii. No. 72, 

 June, 1898) a similar occurrence is recorded. 



III. When birds build covered nests the eggs are white, spotted 

 finely with red, black, or brown, e.g. the Wren's, Chiffchaff's, 

 Swallow's; or pure white, e.g. the Dipper's. The House- and 

 Tree-Sparrows are exceptions. 



IV. Nocturnal birds lay white eggs, as the Short-eared Owl ; 

 or nearly white, as the Nightjar. Protective colouring is not 

 needed in such cases, as the birds sit on their eggs throughout 

 the day. 



V. The eggs of the Accipitres are safe under the parental 

 guardianship. They are pure white, white slightly spotted with 

 red, or boldly blotched with red, or in some cases the ground 

 colour is entirely hidden by the overlying red. 



Here again the exceptions to the rule present great difficulties. 

 Some of them are interesting enough to have attracted the atten- 

 tion of Dr. Wallace and Prof. Poulton. 



(a) All the breeding habits of the Cuckoo are strange and 

 abnormal. Until more is known about them we cannot hope for 

 a satisfactory explanation of the variability of its eggs. 



(b) It is a surprising fact that the Wood-Pigeon, which 

 makes an open nest, lays pure white eggs. Dr. Wallace* and 

 Prof. Poulton f give the following explanation: — They suggest 

 that the egg is white as a protection from below ; that the Wood- 

 Pigeon builds a flimsy wicker nest, through the bottom of which 

 the eggs can be seen ; but that, being white, they are incon- 

 spicuous against the blue sky. [Dr. Wallace expresses it rather 

 differently. After remarking that light may be seen through the 

 nest from below, he says : — " It is a difficult matter to discover, 

 from beneath, whether there are eggs in the nest or not, while 

 they are well hidden by the thick foliage above."] It seems 

 hardly possible that this is the true explanation. Wood-Pigeons' 

 nests are not always of the wicker type ; and, if it is an advantage 



* ' Darwinism,' p. 213. 



f ' Colours of Animals,' p. 62 ; cf. also Beddard's ' Animal Coloration.' 

 p. 115. 



