482 



LAND ANIMALS 



which present favorable environmental conditions, ice-free sea, with 

 rich food supply, protection from storm, good insolation, and, above 

 all, protection from predaceous mammals, especially the ubiquitous 

 arctic fox. Some parts of western Greenland are accordingly very 

 densely populated with breeding birds, while northeast Greenland, 

 with unfavorable ice conditions, has relatively few. 17 The west coasts 

 of Spitzbergen, washed by the Gulf Stream, are more favorable than 

 the east, and here as well as in the Bear Islands, it is the south and 

 west exposures which are protected from the raw north and east 

 winds, that are most heavily colonized by birds. 16 The density of the 



Fig. 123. — A bird island: Eiderholm in southwest Iceland. After Hantsch. 



bird population may vary from year to year at the same locality. In 

 King Charles Land, only 9 species of marine birds were found in 

 1889, when ice conditions were unfavorable, whereas 21 species were 

 reported in 1898. 



Arctic sea birds nest either on steep rock cliffs which rise from 

 the sea or on small islands. The cliffs are inaccessible to predators, 

 and the islands are, or become so, when the ice has broken up in 

 spring. These two types of breeding place are adopted by different 

 birds ; the arctic sea birds may be divided into cliffs breeders and island 

 breeders. 18 



The eider ducks {Somateria molissima and S. spectabilis, Fig. 123) 

 form the principal element in the population of the arctic bird islands. 

 They take up their breeding residence only after the break-up of the 

 ice. Where they are undisturbed they may nest so close together that 

 it is impossible to walk without stepping on them. 19 Barnacle geese, 

 knots, phalaropes, and terns are associated with the eiders. All live 





