470 EIGHTH PACIFIC SCIENCE CONGRESS 



(a) The Primary Tropical Fauna 



BOOBIES 



Sula piscatrix, dactylatra and leucogaster 

 These three tropical boobies are found throughout the three oceans, 

 where they have sympatric relations. The Panama and Indo-Malayan 

 water gaps have obviously contributed to the distribution pattern ob- 

 taining at the present day. However, though all three species nest 

 close to the outer islands of the Indo-Malayan region none actually 

 breed on the islands in the shallow seas within it except on Goenoeng 

 Api in the South Banda Sea. Of the three species, S. leucogaster pene- 

 trates furthest in this area and, it forages throughout the entire extent 

 of the northern Australian coast. Two species of the Booby group, S. 

 nebouxii and S. variegata, have differentiated on the west coast of South 

 America, where they have circumscribed ranges. 



TROPIC-BIRDS 



Phaethon spp. 



P. ruhricauda and P. lepturus have similar relations in the Indo- 

 Pacific as the three Boobies just referred to. P. rubricaudus is, however, 

 unrepresented in the Atlantic Ocean. 



P. aethereus occurs in the Atlantic and has penetrated to the central 

 eastern Pacific by means of the Panama gap but has not extended widely 

 in this Ocean. Probably through the Tertiary water way between the 

 Mediterranean and Indian Oceans it has obtained entry into the north- 

 west of the Indian Ocean and established nesting stations in the Per- 

 sian Gulf. It does not occur elsewhere in this ocean. In general, the 

 distributions of P. ruhricauda and P. aethereus are allopatric. 



FRIGATE-BIRDS 



Fregata spp. 

 Fregata ariel and F. minor have sympatric relations in the tropical 

 zones of all three oceans, the Panama and Indo-Malayan water gaps 

 having facilitated their colonisation of appropriate habitats. F. mag- 

 nificens of the central Atlantic crosses the isthmus of Panama with com- 

 plete freedom (Murphy, 1936, pp. 859, 920) and has reached a western 

 outpost in the Galapagos. 



TERNS 



Sterna fuscata and S. ajiaetheta 



These two similar species occur widely in the Indo-Pacific Oceans 



and through the Panama water gap have peopled the western Atlantic. 



The distribution suggests the Indo-Pacific basin as the origin of the 



group. S. lunata is a derivative of 5. anaetheta in the southern central 



