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 nést 
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 we often find among birds that are nearly 
related, a suspicious family likeness, regardless of the 
