SWAMPS AND SHORES 483 



peacefully together and feed in the adjoining shallow sounds and 

 bays. 18 



The bird cliffs are usually vertical rock walls rising from the sea, 

 populated at the breeding season with vast numbers of birds of rel- 

 atively few species (Fig. 124). Every ledge and inequality in the rock 

 is occupied. The community may include only a few related species, 

 as in Spitsbergen, or may be a varied assemblage, as in the Bear 



Fig. 124. — A bird cliff: breeding colony of the booby (Sula bassana) on the 

 Bass Rock Cliffs, Scotland. After Meerwarth and Soffel. 



Islands. 18 At Godthaabs-fiord, in West Greenland, a great cliff is 

 occupied by Larus hyperboreus, L. leucopterus, and Rissa tridactyla, 

 while in other localities the breeding birds may be mostly murres. 20 

 Each species usually has special habits. The vast numbers of birds in 

 such rookeries as the cliffs of the Bear Islands can scarcely be exag- 

 gerated. 18 



Most of the inhabitants of the sea-bird cliffs, and especially the 

 auks,* lay their eggs without a nest, directly on the rock. They usually 

 have only one or two eggs, and press these into their body so that 

 they are completely covered. The nest might be said to be in the 

 parent's body. If these birds are driven suddenly up, they usually 



* Alca, Uria, Fratercula, Ceppus, and Plautus. 



