54! On the Production of Colour in Birds' Eggs. 



in the nest. To such intruders pure white eggs would be 

 s conspicuous and gratuitous advertisement, and the birds 

 would be exposed to undue danger while in the egg. As 

 has been remarked hundreds of times before, we accordingly 

 find that white eggs, and especially eggs of shining or pearly 

 whiteness, are almost always found in nests which either 

 conceal the eggs completely, or which are themselves com- 

 pletely concealed. Thus the cookatoos, parrots, parrakeets, 

 and othei' members of the family, in almost all cases, 

 build in holes of trees, usually high up and quite out 

 of reach. Owls build in holes of large gum trees ; 

 kingfishers, including the laughing jackass (Dacelo gigas), 

 in holes of trees or banks ; the diamond birds, the roller, and 

 bee-eater, in holes in trees or in burrows. The penguins 

 and many of the petrels lay their eggs at the extremities of 

 long burrows in the ground, facing the sea. The eggs of all 

 of these groups of birds are white. 



The eggs of the doves, pigeons, and podai'guses are 

 beautifull}^ white, often shining as if enamelled. The birds 

 construct slight nests of twigs, placed crosswise on horizontal 

 branches of trees. Much light can pass through the inters- 

 tices between the twigs, and it is a difficult matter, even for 

 the trained human eye, to detect from below whether there 

 are eggs in the nest or not. Here the white, light-reflecting 

 eggs are at a positive advantage. 



The Australian finches conceal their eggs in the depths 

 of relatively huge covered baggy nests, provided with side 

 spout-like entrances. The eggs are in no way visible from 

 without, are securely stowed away, and are pure white. 

 All of the English finches, on the contrary, lay in open 

 nests, and the eggs are spotted, usually, too, on a neutral- 

 tinted ground. In this case we may presume that we have 

 preserved the ancestral type in Australia. 



Since a glaring uniform white must be a dangerous colour 

 for exposed eggs, we are not surprised to find that variations, 

 favourable to preservation, have been originated and preserved, 

 and that colour is now a protection to the great majority of 

 eggs. Tn all cases we have to consider two questions : 

 (1) How could the colour have been acquired ? and (2) How 

 is the colour now protective or otherwise beneficial ? That 

 natural selection would be called into play to preserve 

 favourable markings or tints we may allow, but we believe, 

 with Mr. Seebohm, that " natural selection is not the cause 

 of evolution " in this case, '' but only its guide." 



