THE RE-ENTRANTS 309 



fig. 187. Yellow-bellied sea snake. 



YELLOW-BELLIED SEA SNAKE: PelaVlis j)latuniS 



Size: Up to 3 feet. 



Distribution: Ecuador to the Gulf of California. West to Africa. 

 Identification: The dorsal half of the body is dark bluish brown, and the 

 ventral half bright vellow to orange. The tail is yellow with dark bars. 

 Habits: Same as for the family. 



BIRDS: Glass Aves 



There are several families of birds that feed by di\ing in the sea, particularly 

 near land, and a great number that float or fly over the sea. None of these is 

 exclusively a marine group since they go beneath the surface only to feed. The 

 swimmer may be treated to seeing birds swimming beneath the surface, where he 

 will be startled bv the speed these animals can attain. Underwater photography 

 of diving birds is a fascinating pastime. (We refer the reader to the excellent 

 field guides to birds, given in the Bibliography, that are a\'ailable for identifica- 

 tion.) A list of prominent families that dive to feed in the North American seas 

 and swim below the surface follows: 



Loons (Gaviidae) 



Grebes (Golvmbidae) 



Cormorants (Phalacrocoridae) 



Some ducks and mergansers (Anseridae) 



Auks, murres, and puffins (Alcidae) 



Many other birds dive just below the surface but do not swim under water. 

 Some of these are shearwaters, petrels, tropic birds, pelicans, gannets, man-of-war 

 birds, some ducks, gulls, and terns. 



MAMMALS: Class Mammalia 



Four groups of mammals enter the sea: sea otters, seals and walruses, manatees, 

 and whales and dolphins. The last two groups are exclusively marine, never 

 appearing on land. The others enter the sea mainly to feed, although the sea 

 otter has been driven to become more and more exclusi\'ely marine in its habits 

 because of persecution by man. 



Carnivores: Order Carnivora 



There is some confusion surrounding the term "carnivore." Used as a reference 

 to habits it means "of flesh-eating habits" and may apply to sharks, killer 



