246 THE BIOLOGY OF MARINE ANIMALS 



cea, etc., on the shore when the tide is out, and also fish and play the role 

 of scavengers in coastal waters. Terns are mainly coastal birds of warmer 

 waters, although some species migrate far north to breed, notably the arctic 

 tern Sterna paradisea. Their food is mainly small fish which they secure 

 by plunging from the wing into the sea. To a minor extent small cuttlefish, 

 Crustacea and pelagic molluscs are also taken. 



Conspicuous fishers in coastal waters are cormorants and shags (Phala- 

 crocoracidae). Their food consists chiefly of fish and Crustacea, obtained 

 by diving from the surface. Cormorants possess hooked mandibles, and 

 employ feet and wings for propulsion under water. Pelicans (Pelicanidae) 

 frequent coasts and estuaries, where they dive for fish in shallow waters. 

 Frigate-birds (Fregata) are tropical and completely aerial in habits. They 

 feed on fish, molluscs, jellyfishes, etc., picked up from the surface, and they 

 also force other birds such as gulls and terns to release their catch. 



Characteristic coastal and offshore birds of the continental shelf in the 

 northern hemisphere are the auks, guillemots and puffins (Alcidae). 

 Their food consists of planktonic Crustacea and fish, which are captured 

 by diving from the surface. Gannets and boobies (Sulidae) are also fish 

 eaters, which plunge from the wing and pursue their prey beneath the 

 surface. These birds generally have lance-shaped bills suited for catching 

 fish and larger crustaceans. 



In the southern hemisphere the role of the Alcidae is filled by penguins 

 and diving petrels. Some penguins are pelagic in the non-breeding season, 

 others sedentary in habits. Their food consists almost entirely of fish, 

 cuttlefish and Crustacea, obtained by diving. King penguins consume 

 squid and fish; smaller penguins, such as the Adelie and Gentoo, feed 

 extensively on krill, especially Euphausia. The diving petrels of the southern 

 hemisphere (Pelecanoididae) are usually found in coastal regions, although 

 some species are partly pelagic in habits. Their food consists largely of 

 small fish and Crustacea, obtained by diving. 



Among the characteristic pelagic birds are the Tubinares — petrels, 

 shearwaters, fulmars and albatrosses. Most of these birds spend much of 

 their lives far beyond sight of land. Their food consists to a large extent of 

 surface plankton, including Crustacea, jellyfish, molluscs, as well as squid 

 and small fish. They frequently glean their food from the surface as they 

 skim over the waves, but they sometimes settle to swim about and feed 

 when food is concentrated, or dive short distances below the surface. 

 With the large-scale exploitation of marine resources now practised by 

 man, namely whaling and trawling, some sea birds, notably fulmars, 

 obtain a substantial amount of their food from the offal thus afforded. 

 Indeed Fisher (26) advances evidence for the thesis that the phenomenal 

 increase in numbers of the fulmar {Fulmarus glacialis) in the North Atlantic 

 during the past three centuries is the result of the additional food provided 

 for these birds by the activities of whalers and, later, steam trawlers. 

 Other pelagic birds have diets as follows: penguins (fish and plankton 

 feeders); kittiwakes and swallow-tailed gulls (fish, Crustacea, molluscs, 



