Caspian Tern (Sterna caspia) : This large, cosmopolitan 

 tern primarily breeds inland in Europe (including the Baltic Sea 

 and interior USSR) and North America, along sea coasts and 

 inland along rivers and lakes, migrating and dispersing 

 southward during the nonbreeding season, remaining very 

 close to continental coastlines. Apart from its winter status in 

 Japan as a visitor, the Caspian tern is rare or uncommon in 

 southeast Asia (Harrison. 1985: King & Dickinson. 1987): 

 records are from Cambodia. Laos, extreme south Vietnam, and 

 Thai land, but not from Singapore (Hails, 1987). We observed 

 five Caspian terns. Hying east and south, on the last day of the 

 cruise. 31 October, in Singapore Roadstead. Absent elsewhere, 

 this species had a density of 0.49 birds/10 knr here. 



Black-napcd Tern [Sterna sinnatrana) : A small, mostly 

 white, rather delicate tern, the black-naped is mainly sedentary, 

 breeding in the warm watersof the western Pacific and southeast 

 Asia. It is primarily a resident of seacoasts and offshore islets 

 (Harrison. 1985; King & Dickinson, 1987), extending eastward 

 no further than 180° longitude (King, 1967). 



We recorded two, one adult 80 km north of Ulithi Atoll 

 (District of Yap, Micronesia) and a juvenile approximately 

 550 km east of the Philippines. 



Gray-backed or Spectacled Tern (Sterna lunata) : The 

 gray-backed tern breeds in the Hawaiian, Phoenix, Line, and 

 Tuamotu Islands, plus several other island groups to the 

 southwest. At sea, it occurs as a vagrant or migrant w ithin these 

 approximate boundaries (King, 1967; Harrison, 1985). Their 

 range is poorly known, probably because they are similar to. 

 and often associated in small numbers with, the abundant sooty 

 tern. 



We recorded eight gray-backed terns in the Line and 

 Phoenix Islands. Two adults w ere seen on 20 September within 

 30 km of Maiden (04°03'S. I55°01'W). Within the Line 

 Islands, gray-backed terns are known to breed on Christmas. 

 Jarvis. and Maiden (Clapp. 1967). thus we were probably 

 observing birds from the Maiden colony (500-1.000 birds), 

 which would have been breeding at that time (Clapp. 1967; 

 Grossman & Grossman. 1974; Garnett. 1983). 



In the Phoenix Islands we saw two birds centrally in the 

 group and six ( including one juvenile ) north of McKean. Gray- 

 backed terns breed on Enderbury (N = 10.000 birds). Phoenix 

 ( N = 1 .800 birds), and McKean ( N = 23.000 birds) < King. 1 973; 

 Garnett, 1983). 



Gray-backed tern densities were greatest in the Phoenix 

 Islands (0.20 birds/10 km>. close to the largest breeding 

 colonies in the world. Because breeding was in progress, most 

 tems were likel) to be on or near land. 



Bridled or Brown-winged Tern (Sterna anaethetus) : 

 Frequenting offshore waters and open ocean in the tropics and 

 subtropics, tins species is the ecological counterpart of 

 S. lunata in the western Pacific. We identified three bridled 

 terns in Singapore Harbor; they are known to be offshore 

 residents of the Malay Peninsula (Hails. 1987; King & 

 Dickinson. 1987). 



Sooty Tern (Sterna luscata) : The most abundant seabird 

 in the tropical Pacific, the soots tern breeds colonial!} in large 

 numbers on almost every island group. Ii ranges widely 

 between the tropics of Capricorn and Cancer. 



We observed this species in the Line, Phoenix, and 

 Gilbert Islands and Micronesia. It was the most abundant bird 

 observed on the cruise (N = 2.305), nearly eight times more 

 numerous than the secondmost common species, the wedge- 

 tailed shearwater (Table 4). Sooty terns comprised 62.8% 

 of the total number of birds observed (Fig. 4). 



Sooty terns ranged throughout the Line Islands, with 

 heavier concentrations near Christmas and Jarvis. Major 

 colonies, of approximately two million each, exist on these two 

 islands. The Christmas populations have declined drastically 

 in recent years (from an estimated 15 million 10 years ago) due 

 to predation by rats and cats, direct human exploitation for 

 food, and reproductive failure due to the 1982-1983 El Nino 

 Southern Oscillation (King. 1973: Gould. 1974b; Garnett. 

 1984; Schreiber & Schreiber. 1984; E. Schreiber, personal 

 communication). 



In Region II. sooty tern populations are estimated at 

 around four million (Gould, 1974b). Here we observed the 

 highest density of all species (43.27 birds/ 1 knr), eight times 

 greater than sooties in the Line Islands (Table 2). Sooty terns 

 are abundant year-round in the Phoenix Islands, with highest 

 densities recorded from October to December (Gould. 1974b). 



Their numbers at sea depend on their breeding cycles, 

 which are often complex and unpredictable, even within a 

 single island. In 1965, and from 1988 to 1990. Caroline Atoll 

 had 19 colonies, each on a different cycle, giving rise to egg- 

 laying in virtually every month (Clapp & Sibley. 1971a: 

 Anne Falconer, personal communication; Kepler et <;/.. 

 Subchapter 1.2, this vol.). 



In Region III (Gilbert Islands) smaller numbers of sooty 

 terns were observed (N = 1 13): we found moderate densities 

 (4.00/10 knr). although the species is reported as uncommon 

 at sea (Amerson. 1969). Our cruise track passed close to 

 Aranuka. which is thought to harbor breeding colonies 

 (Amerson. 1969). 



In Region IV (Micronesia), we only observed sooty terns 

 south of Kosrae and Pohnpei (N = 201): 200 of these were 

 members of a single feeding flock. This species is known to 

 breed in small numbers in Micronesia on Pohnpei. on several 

 uninhabited atolls in the northern Marshalls (Baker. 1951; 

 Amerson. 1969). and on Helen Reef (Engbring. 1983). 



Although ranging entirely across the Pacific Ocean through 

 southeast Asia into the Indian Ocean (Harrison. 1985). sooty 

 terns have been seen only infrequently in the far western 

 Pacific (Baker. 1951; Gould. 1974b). The POBSP found that 

 the perimeter of their peripheral breeding localities is also the 

 normal limit of their pelagic dispersal, and records beyond this 

 have historically been attributable to climatic disturbances 

 such as typhoons (Gould. 1974b). 



Sooty terns, highly gregarious feeders and breeders, 

 participated in 7 1 .49! of all 1 4 feeding flocks and contributed 

 70.8'f of all birds within the flocks (Tables 5.7; Fig. 7). Of 

 2,305 sooty terns observed. 1.467 (64' r) were in feeding 

 Hocks, as was also found (65'i ) by Gould ( 1974b). Over our 

 entire cruise track, only 4'i were juveniles, suggesting that few 

 soot) colonies had bred recently. By contrast, during March to 

 May 1990 in the Line Islands, a much larger proportion of 

 juveniles were observed (ICBP. 1990). 



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