462 EIGHTH PACIFIC SCIENCE CONGRESS 



of Dr. Robert Cushman Murphy. It is an inspiration to others to re- 

 intensify the ornithological exploration of other islands in the Indo- 

 Pacific and the collection of birds at sea to build up our store of facts 

 on the nesting and the foraging ranges of the pelagic birds. During 

 the course of the work, S. Ekman's "Zoogeography of the Sea," the re- 

 vised English translation of his stimulating synthesis, "Tiergeographie 

 des Meeres," was published, and it also has been laid under contribution. 



II. Factors in the Problem 



Though the three major oceans, the Pacific, Indian and Atlantic, 

 contain many faunal elements in common, the Pacific is notable for the 

 following characteristics: 1. A rich development of petrel forms un- 

 surpassed by either the Indian or Atlantic Oceans, and approaching 

 that of the Southern Ocean in number of species and races. 2. A strong 

 development of terns. 3. An entire lack of gulls in the island archi- 

 pelagoes, they being confined to the peripheral fringes. 



Environmentally a significant characteristic of the Pacific Ocean, 

 as compared with the others, from the standpoint of sea-bird colonisa- 

 tion, is the wealth of islands over a large joart of its area and in most 

 of its hydrologic zones, as compared with the more peripheral distribu- 

 tion of islands in the main basins of the Indian and Atlantic Oceans. 

 In this respect much of the Pacific Ocean resembles the circumpolar 

 Southern Ocean. The eastern portion of the Pacific, however, is sin- 

 gularly lacking in islands, this abyssal region constituting an important 

 barrier in the continuity of faunas which depend on shallow shelves 

 and banks, and Ekman (1953, p. 73) considers it as causing "the most 

 pronounced break in the circumtropical warm-water fauna of the 

 shelf." The main effect on the pelagic sea-birds has been the depriva- 

 tion of nesting sites in this area, and the geographical isolation thus 

 contributed to has permitted some subspeciation to have gone on. 



During the Tertiary and Pleistocene one hydrological barrier in 

 particular and three physical or geographical barriers have been of 

 paramount importance in controlling the spreads and dispersals of 

 pelagic sea-birds within and between the three major oceans. They 

 have served as lock-gates, as it were, in regulating the ebb and flow of 

 species' movements. They are: 



1. The barrier of tropical, equatorial, waters was breached re- 

 peatedly during the Pleistocene glaciations, enabling the transgression 

 through them of northern and southern elements, giving rise to the 

 phenomenon of anti-tropicality or bipolarity (for a modern discussion 

 see Hubbs, 1952, p. 324). Ekman (1953, p. 257) postulates such pene- 

 trations during the greater part of the Tertiary, and indeed pre-Glacial 



