rod-foots than in September 1988. These were primarily 

 juveniles dispersing after a successful breeding season. 



On 1 3 October we observed 30 red-foots in the vicinity of 

 Pohnpei. Most of these were participants in two feeding flocks, 

 one of which was the second largest on the cruise. Both flocks 

 developed immediately after a storm. The proportion of light- 

 to dark-phase birds at Pohnpei was 22:9. Red-foot density was 

 highest on this day ( 1 .62 birds/10 km : ). Overall densities were 

 1 times greater in Micronesia than elsewhere, due to the large 

 numbers seen feeding near Pohnpei. 



Brown Boobv (Sula leuconaster) : This pantropical species 

 ranges widely in the Pacific and breeds on almost every island 

 group, although typically in smaller numbers than red-foots. 

 The brown booby, less dependent on the tropical blue waters 

 preferred by the other two species, is often found in inshore 

 waters, including harbors and estuaries, which are more polluted 

 and more accessible to man. Because of this. Nelson ( 1978) 

 considers that the brown booby has suffered more than its 

 congeners, probably accounting for their small numbers in 

 populated areas such as Micronesia and the South China Sea. 

 Brown boobies are seldom encountered more than 80 km from 

 land (King. 1967), but Harrison (1985) noted that there is 

 evidence to support small-scale dispersal. 



We observed only nine individuals in the Line Islands, 

 Caroline Islands (Micronesia), and South China Sea. We 

 attempted to relate these individuals to nearby colonies. In the 

 Northern Line Islands (two sightings at 02°02'N, 157°37'W) 

 the closest colony was Christmas Island (N = 100), 32 km 

 distant. 



In Micronesia, the only brown boobies (two adults) were 

 at 10°03'N, 150°02'E, approximately 150 km northwest of 

 Magur, Namonuito Atoll, Truk (07°N, 147°E), and 220 km 

 from uninhabited East Fayu Island, Truk (08°N. 151°E). 

 Although brown boobies nest on uninhabited islands in the 

 Marshall Islands (Amerson, 1969;SPREP, 1989),theircolonies 

 are rare and little known in the Caroline Islands. Some birds 

 were seen at Truk in 1945 (Baker, 1951). and earlier this 

 century, "incredible numbers of seabirds." which Nelson ( 1978) 

 suspects may have included brown boobies, were reported on 

 West Fayu, Gaspar Rico, and Magur. Nelson further notes that 

 "East Fayu is also a breeding site," implying a colony of this 

 species. Although the ornithology of these islands is virtually 

 unstudied (NID, 1945: Nicholson & Douglas, 1969; Owen, 

 1 97 1 , 1 977a, b; Ray Fosberg, personal communication), several 

 colonies of brown boobies may still exist in the Caroline 

 Islands. It is unlikely that the brown boobies we observed were 

 from the Marshall Islands, the nearest known colony of which 

 is Enewetak. about 1.400 km to the east. 



Seabird information in the more remote islets of the 

 Philippines and in the South China Sea is similarly scarce and 

 outdated (Delacour& Mayr. 1946: King & Dickinson. 1975; 

 Nelson, 1978; Harrison, 1985). Nelson states that "the status 

 of the Brown Booby here is little known. There are some, could 

 be many and may be few." Their only known nesting colony 

 near Balabac Strait is at Tubbataha Reefs (68°N, 1 20°E) in the 

 central Sulu Sea (Worcester. 1911, in Nelson, 1978, IUCN. 

 1988a). 



In the South China Sea, we observed five brown boobies 

 in the Balabac Strait close to numerous islands off the southern 

 tip of Palawan (07°44'N, 1 16°58'E) and near northwest Borneo 

 (05°92'N, 114°03'E and 04°40'N, 113°20'E). The closest 

 known colony is Spratly Island (Nan-Sha Reefs), evidently the 

 only remaining colony of brown boobies in Malaysian waters 

 that has not been overexploited (Nelson, 1978) that was still 

 extant 16 years ago (Haile, 1964, in Nelson, 1978). Both 

 locations were within 30 km of coastlines. Our brown boobies, 

 approximately 200 km west of this reef and flying east, could 

 have originated there (or on several other little-known islands 

 in the southwest Sulu Sea). 



Overall densities of brown boobies were low everywhere, 

 but were four to six times higher in the Sulu Sea-South China 

 Sea than in the Line Islands and Micronesia, respectively 

 (Table 2). These distributional patterns are most likely due to 

 the proximity of our cruise track to potential breeding islands 

 and nearshore waters. We saw no brown boobies in feeding 

 flocks. 



Family Fregatidae 



Frigatebirds were seen throughout our cruise track except 

 for the Gilbert Islands and the Philippine Sea. The only 

 identifiable species was the great frigatebird (Fregata minor): 

 two distant, unidentifiable frigatebirds were seen in the central 

 South China Sea. Surprisingly, no lesser frigatebirds (F. oriel) 

 were seen, even though they winter in the western tropical 

 Pacific (Sibley & Clapp, 1967). Densities (Table 2) were 

 highest in the Phoenix Islands (0.30 birds/10 km 2 ), where the 

 largest populations in the Pacific breed, and lowest in 

 Micronesia, where frigates are known to be scarce. Overall, 

 frigates accounted for only 0.7% of all birds observed on the 

 cruise (Fig. 4). 



Great Frigatebird (Frcvcita minor) : We observed 23 great 

 frigatebirds in the Line, Phoenix, and Caroline Islands. Densities 

 were highest in the Phoenix Islands (Table 2), where over 

 30,000 are known to breed (Stoddart. 1976). 



We saw only five great frigatebirds in the Line Islands, 

 where around 13,000 breed (Clapp. 1967; Garnett 1983; 

 Kepler et al, Subchapter 1.2, this vol.). These low numbers 

 may reflect the fact that birds are concentrated on and near 

 colonies during the breeding season (Clapp, 1967; Kepler 

 et al.. Subchapter 1.2, this vol.). 



In Micronesia, we saw only one frigatebird, part of a 

 large feeding flock near Pohnpei. Evidently frigatebirds are 

 infrequent in the Caroline Islands (Baker. 1951; King, 1967; 

 Pratt et al., 1987). We located only one reference to breeding 

 colonies of this species in this region (Niering, 1961 (.otherwise 

 they "are probably resident, especially in the eastern part" 

 (Baker, 1951). 



The juvenile frigate in the southwest Sulu Sea (08°02'N. 

 1 17°28'W) and the adult in the South China Sea near Vietnam 

 (05°48'N, 106°5 l'E) could have come from anywhere, as they 

 may wander thousands of kilometers (Sibley & Clapp, 1967; 

 Nelson, 1975). Great frigatebirds were minor participants in 

 feeding flocks, contributing only 0.3% of the total numbers 

 (Table 8). 



239 



