388 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



hydroids, sponges, foraminifera, corals, rhabdopleurids, tunicates 

 and bivalves, and curious polyzoans grow upon them, using them as 

 a support to maintain themselves above the mud or sand. But 

 crinoids have one distinct advantage over mussels in that fishes 

 never eat them. 



All sea animals are undoubtedly as complicated in their relation- 

 ships to others as are the mussels and the crinoids ; each feeds upon 

 a more or less extensive list of organisms, and in its turn serves 

 as a source of food for many others. 



The enemies of the smaller animals are mostly the larger and pre- 

 dacious ones. The enemies of the plantlike types are chiefly the graf- 

 ters and the food stealers. The enemies of the larger creatures, as 

 the sharks and whales, are the much smaller blood-sucking or in- 

 ternal parasites which, though much less conspicuous, are very 

 numerous and just as dangerous. 



The birds of the seashores call for brief enumeration. The gulls, 

 very numerous in northern regions, are chiefly scavengers, feeding 

 upon whatever is cast up on the beaches or they are able to find upon 

 the flats when the tide is out ; ravens and crows compete with them 

 along the shores, but are never very numerous, and are very much 

 less agile on the wing; both these last two prefer to consume their 

 booty in the woods, and often carry shells, starfish, and urchins for 

 some distance inland. Terns and skimmers eat crustaceans and small 

 fish, and fish and sometimes squid form the diet of the cormorants, 

 pelicans, bobies, frigate birds, tropic birds, and gannets. The reef 

 and night herons catch fish and various of the larger crustaceans, 

 while the very numerous shore birds eat aquatic insects, crustaceans, 

 marine worms, and small mollusks which they catch along the 

 water's edge or on the rocks and beaches, some, like the phalaropes, 

 also on the surface of the sea. Interesting, but relatively unimport- 

 ant and not numerous in species, are the fish-consuming hawks, 

 eagles, kites, and vultures. The osprey is known to almost every- 

 one; so is the bald eagle, which often robs him of his prey as the 

 parasitic skuas and jsegers do the gulls and terns. In the Aleutian 

 Islands this eagle is one of the most abundant land birds along the 

 shores, and is much easier to shoot than the small birds, which here 

 are very shy. In the harbors of the East the kites, soaring over the 

 water on the watch for scraps, look strange to us, accustomed as we 

 are to gulls alone. The condor and the California vulture frequent 

 the beaches more or less, and the nests of the latter often contain 

 mussel shells. Two of the cormorants, one, now extinct, but form- 

 erly common in the Commander Islands, the other living in the 

 Galapagos group, one auk, formerly abundant on the north Atlantic 

 coasts but now extinct, and all the penguins, are flightless. 



Of other seacoast creatures there are the seals, which live on fish, 

 the walrus, which live on mussels', and the sea otter, now very rare 



