480 LAND ANIMALS 



fur, is confined to the northern Pacific coasts of America and Asia. 

 Its fully webbed hind feet adapt it to aquatic habits much more com- 

 pletely than any other of the Mustelidae, so many of which frequent 

 fresh waters. 



The circumpolar walrus (Rosmarus) is distinctively a coastal form. 

 As it feeds on mollusks such as Saxicava, Mya, and Cardium by dig- 

 ging them up with its tusks, it requires shallow water, and is absent 

 from the steep coasts of Greenland. The walrus lives continuously in 

 the water during winter, but comes ashore on land and on ice during 

 summer, especially at the breeding season, and is then covered with 

 hair; during the winter it is hairless. It is gregarious, and was formerly 

 very abundant. Nine hundred specimens were killed in the Bear Islands 

 in the year 1667 within a few hours. It is now present in numbers only 

 on the northernmost of the arctic islands. 



The eared seals (Otariidae) and the true seals (Phocidae) are well 

 adapted to aquatic life, but repair to land or ice for rest and sun and 

 for longer periods at the breeding season and to produce their young. 

 The eared seals are still able to travel overland and to land and climb 

 on rocky shores, in spite of the transformation of their limbs into 

 flippers. Phocidae, on the other hand, are much less mobile on land, 

 and are accordingly confined to shelving coasts and low ice floes and 

 to the immediate vicinity of the water. The crested seal, Cystophora, 

 is sometimes found on ice whose border is 2 m. vertically above the 

 water, and it undoubtedly reaches this height by a single powerful 

 jump from the water, as penguins are also able to do. 



Both types (seals and eared seals) may make long migrations to 

 reach their breeding grounds. The polygamous fur seals assemble in 

 enormous numbers at their rookeries, dominating the landscape as do 

 the penguins and cormorants. The rookeries of the fur seal {Callor- 

 hinus ursinus) in the Alaskan Pribilof Islands are well known 12, 13 

 (Fig. 128). Even since the legal cessation of pelagic sealing, there has 

 been a continuing pelagic loss of about 25% of the births for a given 

 year. The killer whales are suspected of being the carnivore mainly 

 responsible for this loss ; 18-24 14 seals have been found in the stomach 

 of a single one of these wolves of the sea. The true seals, which are 

 monogamous, do not gather in such large numbers. The Greenland 

 seal {Phoca groenlandica) makes great journeys, from Greenland to 

 Spitzbergen and to the Jan Mayen ice, where the young are born; 

 Phoca barbata and Cystophora cristata do not have a breeding migra- 

 tion. 



Coastal birds. — The life of the seacoast is dominated by birds. 

 Wherever there is a tide flat, low tide exposes a great number of 



