Brown Booby 

 Red-footed Booby 

 Pomarine Jaeger 

 Brown Noddy 

 Black Noddy 



All the birds in this category except the 

 Pomarine Jaeger breed in the main Hawaiian 

 islands and are land-dependent to the extent 

 that they normally do not fly out from their 

 roosting area farther than 1/2 day's flight in 

 search of food so that they can return to their 

 roosts nightly. A substantial population is 

 present in the breeding area all year. The 

 Pomarine Jaeger is common off the main Ha- 

 waiian islands only during the winter. In the 

 spring, birds wintering farther south join the 

 wintering Hawaiian population, and both groups 

 migrate north in May and June. Pomarine 

 Jaegers are absent from the study area during 

 the summer. 



2. Species whose numbers decreased grad- 

 ually with increasing distance from land: 



Dark-rumped Petrel 

 Bulwer's Petrel 

 White-tailed Tropicbird 

 Great Frigatebird 

 White Tern 



This category comprises three birds that 

 breed in the main Hawaiian islands — two pro- 

 cellariids and a tropicbird — and two wide- 

 ranging birds that breed in the leeward Ha- 

 waiian chain, in the Line and Phoenix Islands, 

 and in many other tropical Pacific island groups. 

 They travel farther from land during their 

 breeding season than those in the preceding 

 category. The two petrels become more highly 

 land-oriented during the breeding peak, but 

 since they range more widely at sea at the 

 beginning and end of their breeding cycles, the 

 net effect is one of decreased land-orientation 

 compared with the species in category 1. The 

 other three species are present all year in the 

 study area. They range far more widely in 

 search of food than birds in category 1 and 

 must frequently spend the night at sea, which 

 for the frigatebird and the tern is remarkable 

 since neither was observed to sit on the water 

 in the 15 months of the pilot program, and they 

 have very rarely been observed on the water 

 elsewhere in the central Pacific by POBSP 

 personnel. They show a general orientation 

 toward land, however, unlike birds in the suc- 

 ceeding categories. This general orientation 



Figure 27. — Distance-from-nearest-land isopleths 

 superimposed on the theoretical cruise track. 

 Palmyra Island of the Line group is the 

 closest point of land from the southwestern 

 part of the study area. 



toward land is weak evidence that the Hawaiian 

 Islands are the islands of origin for the birds 

 of these species found in the study area. 



3. Species that were observed less fre- 

 quently within 50 miles of land than over 

 100 from land: 



Juan Fernandez Petrel 

 White-necked Petrel 

 Mottled Petrel 

 Black-winged Petrel 

 Kermadec Petrel 

 Herald Petrel 

 Sooty Shearwater 

 Slender-billed Shearwater 

 Christmas Shearwater 

 Blue-faced Booby 

 Golden Plover 



67 



