BIRDS' EGGS 279 



there are limits of coloration beyond which an egg in a 

 ground-nest cannot pass with any chance of survival. 



It is true that unspotted eggs and not inconspicuous may 

 be found in exposed nests, but it is often easy to see why this 

 need not be dangerous. Some birds, like pheasants and 

 partridges, draw leaves or other covering over the nest, and 

 this will also help to conserve the warmth. Some birds, 

 like wood-pigeons, sit very close. Some birds are formidable, 

 as in the case of cormorants and herons, and are not much 

 molested. 



There are some cases where the resemblance of the eggs 

 to the surroundings is very striking. It is often difficult to 

 avoid treading on the eggs of the tern lying in a scraping 

 on the shingly beach. The eggs of the night-jar harmonise 

 beautifully with the mottled ground amongst the furze. 

 The eggs of the cassowary are large, three inches by six, 

 but their emerald hue matches the moss in the jungle. 



(2) The eggs of birds that lay in holes or in covered 

 nests are often white, e.g. in kingfishers, puffins, and owls, 

 and this has been interpreted in terms of the fact that in the 

 situations habitually chosen the eggs are not visible to hungry 

 eyes. It might also be said that in such situations, there are 

 no inimical rays of the sun to be screened off. Perhaps a 

 deeper way of looking at it is to say that the absence of shell- 

 pigment is a primitive feature, as seen in reptiles, and that 

 birds which persisted in having white eggs had to seek out 

 concealed places or build well-covered nests. The humming- 

 bird's very white egg is laid in an open nest, but the nest 

 itself is very well hidden among the leaves. 



(3) There is attractiveness in McAldowie's suggestion 

 that the pigmentation of the egg-shell may be of value in 

 screening off certain rays of the sun, which might injure the 

 developing embryo, especially in much exposed nests like 

 those of rooks. The blue-green pigmentation would be 

 especially useful, but what is lacking is experimental evidence. 

 It is not difficult to find cases which McAldowie's theory 

 does not fit, but perhaps this is not very useful. If the 

 pigmentation be primarily by-play, it may nevertheless be 



