Natural History 439 



The Imprisonment of the Hornbill 



Another hole-nester is the Hornbill, of which various species 

 are found in many tropical lands, and its story is a very strange 

 one indeed. When the eggs are laid and the hen begins to sit, 

 the opening in the tree-trunk is walled up with mud by the cock 

 until only a small orifice remains through which the sitting bird 

 can put no more than her head. The device is doubtless a means 

 of defence against snakes or other enemies, but it involves the 

 imprisonment of the hen during the whole period of incubation. 

 During this time, however, she is by no means left to starve, 

 but is fed assiduously through the "grille" by her devoted mate, 

 who is indeed said to work so hard and to forage so unselfishly 

 that he is worn to a mere shadow of his former self before the 

 task is done. 



Among the tree-nesting birds the most primitive type of 

 wholly artificial nest seems to bt the platform of sticks or twigs 

 made by such birds as eagles, herons, and pigeons. These struc- 

 tures are often of great size, being added to year after year. 

 The simplest platforms are quite flat, but others are more or 

 less cup-shaped, as in the case of crows. Finally, this type reaches 

 its highest point in those birds which add a dome-shaped roof. 



More Complex Structures 



More promising material is used by most of the small birds 

 which nest in trees or bushes, and with pliable twigs, grasses and 

 roots, moss, and perhaps animal hair, much more complex struc- 

 tures are possible. The Finches, for example, make elaborate 

 and beautiful cup-shaped nests, while others, such as the Wren 

 and the Dipper, make spherical nests which can be entered only 

 by a small hole in one side. In addition to the actual structure 

 there is often a distinct lining of specially selected material; for 

 this purpose small feathers, hair, and fine fibres are greatly 

 favoured, but in the familiar case of the Song-Thrush, for in- 

 stance, a complete lining of hardened mud is a characteristic 



