Natural History 441 



built nest among grass, as in the case of the Skylark or the 

 Meadow-Pipit; at other times there may be a bulky heap of 

 vegetation or of other material; the Cormorant, for instance, 

 often raises a mound of seaweed, and some kinds of Penguin 

 build a Spartan nest of stones. Still, again, there may be a 

 mere hollow scraped in the ground, as in the case of the Lap- 

 wing or of the Tern, perhaps with a lining, a pretence at a lining, 

 or with no lining at all. Finally, the bird may lay its eggs on 

 the ground without any attempt at a nest, as the Oyster-Catcher 

 does among the riverside shingle. 



Cliff-Nesting 



Somewhere between the tree-nesters and the ground-nesters 

 -ve must place those birds which nest on cliffs, for although a 

 nest on a rock ledge may seem in some ways very like a nest on 

 flat ground, the dependence on inaccessibility rather than on con- 

 cealment makes the habit also akin to tree-nesting. Some of 

 the burrowers, like the Puffins and the Petrels, might well be 

 classed in this group as their holes are usually on precipitous 

 faces, but more typical are those species which breed on the 

 open ledges, like the Guillemot and the Razorbill. A highly 

 sp ;cialised type of nest, too, is that which is built of mud against 

 th ; sheer rock face, and for this purpose as in the House- 

 Martin the habitations of man are often found to serve as well 

 as natural faces of rock. Sometimes the mud and other materials 

 are made more coherent by the addition of the salivary secretion 

 of the builders, and with the Edible Swift of Borneo this sub- 

 stance, like hardened glue, forms practically the whole structure 

 anr 1 is the source of the "bird's-nest soup" beloved of the Chinese 

 gourmet. 



Tht Use of Old Nests 



Many birds return to their old nests and use them again 

 and again, while other kinds habitually build afresh each year 



VOL. II 10 



