<26 SEA-BIRDS 



only in the Palearctic Region. This appears to be the only group of 

 sea-birds whose evolutionary radiation may have taken place from 

 the north; the Arctic and neighbouring parts of the North Pacific 

 and Atlantic appears to be the origin of the gulls. The terns (sub- 

 family Sterninae) number thirty-nine, of which twenty-three breed 

 in the North and twenty-two in the South Pacific, nineteen in the 

 Indian Ocean, nineteen in the North Atlantic, fifteen in the South 

 Atlantic, ten in the Mediterranean, two in the Antarctic, two in the 

 Arctic and one inland only in South America. The radiation of terns 

 appears to be pretty general over the world's seas, and they may 

 have originated in the tropics, perhaps in the Indian Region. The 

 skuas (subfamily Stercorariinae) have only four species, one of which 

 {Catharacta skua, the great skua) has its breeding-headquarters in 

 the Antarctic; it also breeds in the South Pacific, South and North 

 Atlantic. The other skuas have an arctic breeding-distribution which 

 extends into the North Pacific and North Atlantic. The three skimmers 

 Rynchops belong to a separate family, Rynchopidae; North Atlantic, 

 South Atlantic and South Pacific each have two; the Indian Ocean 

 has one. Some workers regard them as all of one species. 



The family Alcidae (the auks) take the place in the north of 

 the penguins of the south. Undoubtedly their origin has been in or 

 not far from the Bering Sea. Of the twenty-two species, sixteen 

 belong to the northern part of the North Pacific, twelve to the Arctic 

 Ocean north of the Circle, and six to the northern part of the North 



Atlantic. 



This concludes the list of sea-birds belonging to groups of super- 

 family or higher status whose evolution has been marine. There are 

 several further (secondarily marine) groups which contain sea-birds, 

 or part-time sea-birds; thus all four members of the order Gaviae 

 the divers, breed in the Arctic, and North Atlantic and Pacific 

 regions, and winter at sea on the coasts of the oceans. Many of the 

 twenty species of grebes, order Podicipedes, are marine outside 

 the breeding-season, and six of them visit the coasts of the North 

 Adantic at that time. Among the geese and ducks many (see Appendix, 

 p. 295) are partly marine, and some {e.g. eiders and scoters) are 

 largely marine in the breeding — as well as in the ofF-season: two eiders 

 and three scoters breed in the North Atlantic-Arctic. Among the waders 

 (Charadriidae) the subfamily Phalaropinae contains only three 

 members, all of which breed in the Arctic, North Adantic and North 

 Pacific, and two of which winter in the open sea. 



