BIRDS' NESTS AND EGGS 355 



colour, and they build nests concealed in holes. The Swift 

 makes its rude nest in a hole ; it has no means of protecting 

 itself or its eggs from enemies, and consequently retires to 

 such a site where it can rear its young in comparative safety. 

 So, in like manner, the sombre Sand Martin for a similar 

 reason seeks the sand-banks. Sparrows do not build domed 

 nests or lay their eggs in holes because the plumage of the 

 female demands concealment, but from other motives perhaps 

 the result of a deeply-rooted habit acquired during different 

 conditions of life, or inherited from a common ancestor of 

 far more brilliant tints requiring concealment during the 

 nesting season. This rule applies to many other birds. 

 Again, the Wren builds a domed nest, and is yet one of 

 the most soberly arrayed of our native birds. But this is 

 undoubtedly from other motives of safety than concealment ; 

 for from the peculiar structure of her nest few enemies indeed 

 are able to storm her little citadel. Weak and defenceless as 

 this little creature is, she attains by subtlety what she would 

 fail to procure by prowess. The Dipper probably builds a 

 domed nest for the purpose of shielding her eggs and young 

 from the spray which so often surrounds them in her rock- 

 bound watery haunts. Indeed, in the localities she chooses no 

 other type of nest would answer the purpose. The Willow 

 Warblers build domed or partially domed nests, perhaps 

 because a remote common ancestor did the same, but more 

 probably to shield their tender offspring from the moisture 

 which surrounds their usual nesting-place amongst herbage 

 or tall vegetation. The Willow Warblers are an arctic group 

 of birds, breeding in a climate subject to sudden changes of 

 temperature, and this I think may explain their domed nests. 

 As a proof of this I may remark that the Wood Wren builds 

 a somewhat open nest, never lines it with feathers, and avoids 

 all countries where the climate is cool and moist. The Owls 

 almost without exception nest in a covered site, simply because 



