18 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 123 



In early February between 08°00' N and 00°49' S on the 55° E 

 transect, a species of tern was noted flying around the Anton Bruun 

 at night (see table 13). Using spot lights, we obtained good observa- 

 tions, discerning an a/Z-white tern with a slightly forked tail that 

 left, in my opinion, little doubt as to the identity. The birds were 

 quite vocal, emitting short, low notes, especially when two were 

 together. The presence of fairy terns so far out to sea and only at 

 night (none were seen during the daytime watches) is surprising, for 

 the nearest possible source of these birds, the Seychelles Islands, was 

 well over 600 miles to the south and Gygis is usually known as a 

 coastal or inshore species, not a pelagic one (Murphy, 1936). One 

 wonders, however, whether scattered individuals were drawn to and 

 concentrated around the ship at night, thereby becoming conspicuous, 

 and also whether the species might not be as highly nocturnal as the 

 huge eyes and pure white plumage suggest. These observations 

 should remain hypothetical pending future confirmation. 



Discussion 



The distribution of seabird species and numbers is related to 

 oceanographic factors that produce a suitable variety and abundance 

 of food items (Jespersen, 1929; Hutchinson, 1950; Murphy, 1936). 

 Although the data presented in this paper are insufficient in them- 

 selves, it is hoped that the total information gathered during the 

 International Indian Ocean Expedition eventually will provide the 

 basis for a detailed analysis of the factors underlying seabird distri- 

 butional patterns in the Indian Ocean. A noteworthy step in this 

 direction has been made recently by Bailey (1966) for the important 

 region of upwelling off the southern Arabian coast. The rest of 

 the Indian Ocean, however, awaits comparable attention. 



One of the conclusions that is readily apparent from the data 

 presented in this paper is the paucity of seabirds in the major part of 

 the western Indian Ocean. In this respect, the Indian Ocean is 

 similar to other tropical oceans, which are characterized by the 

 relative infertility of their waters and a consequent scarcity of sea- 

 birds, except in the vicinity of land, either islands or continental 

 coasts, and regions of local enrichment. It was only in the western 

 Arabian Sea and below the subtropical convergence, regions where 

 upwelling, cooler surface temperatures or other factors permit nutrient 

 replenishment and continued productivity, and near the Seychelles 

 and Mascarene Islands, which provide land necessary for breeding 

 and roosting, that seabirds were at all numerous. But even the 

 maximum numbers (200+ /hour) I recorded in these regions were 

 certainly small compared to what is possible in other parts of the 

 world ocean (see Murphy, 1914; Oordt and Kruijt, 1955), especially 



