322 THE STRUCTURE AND LIFE OF BIRDS chap. 



are other exceptions which require a different explana- 

 tion. Swans, Herons, Pelicans, Cormorants, and Storks 

 lay whitish eggs, and leave them exposed ; but they 

 are strong birds and can protect themselves from 

 enemies, the more easily if, like the Herons, they nest 

 in colonies. On the other hand, the Plover and the 

 Snipe, who have open nests upon the ground, and who 

 could not beat off enemies, lay eggs so like the sur- 

 roundings that it requires a very good eye to see 

 them. Blue eggs, such as the Hedge-sparrow's, Dr. 

 Wallace maintains, are not at all conspicuous among 

 green foliage. 



I shall now mention some of the difficulties that we 

 encounter if we try to press the theory. Pigeons 

 lay white eggs, and, whatever may be said about their 

 being concealed among the leaves, they are often 

 most conspicuous. The Short-eared Owl leaves its 

 eggs on a tump of grass or heather, and they are white 

 like the eggs of other Owls which nest in holes. The 

 case of the Barn-door Fowl counts for nothing. 



The eggs of Gulls are protectively coloured, and as 

 the birds nest in crowds together, they probably need 

 no protection. The same may be said of Rooks' 

 eggs. Moreover the rookery would be visible enough 

 to any egg-seeking enemy, and it is hardly likely 

 the eggs would be saved by any dulness of colouring. 

 The eggs of Hawks and Eagles are not conspicuous, 

 and no enemy is likely to invade their nests. The 

 Redstart's blue eggs are laid in holes, where, according 

 to the theory, we might expect them to be white. 

 Moreover wc often find among birds that are nearly 

 related, a suspicious family likeness, regardless of the 



