Table 11. — Flocking tendency by species 

 or species group 



SUMMARY 



The avifauna of the study area was composed 

 of birds breeding in the North Pacific (Alaska 

 and Siberia: 13 species) and the South Pacific 

 (New Zealand, Australia, and South America: 

 15 species), in addition to those breeding in the 

 nearby Hawaiian group or other island groups 

 of the central Pacific (23 species). In general, 

 breeding species of the Hawaiian area were 

 most abundant from March to September, direct 

 migrants were most abundant from March to 

 May and October to November, and wintering 

 birds from May to November with a peak in 

 October. 



Analysis of the distribution of birds with 

 respect to their distance from nearest land 

 showed that birds breeding in the main Hawai- 

 ian group were most abundant within 50 miles 

 of land, although many were seen as far as 

 700 miles from land. Sooty Terns and Wedge- 



tailed Shearwaters were most abundant up to 

 200 miles from land, and again at 700 miles 

 from land. Direct migrants showed no land- 

 orientation. Wintering birds were most abun- 

 dant farthest from land. 



Birds were not distributed at random in the 

 study area. The area within 50 miles of the 

 main Hawaiian islands consistently maintained 

 the highest sea bird densities. The southern 

 end of the area (between lat. 10° and 12° N.) 

 also maintained high densities even though it 

 was farthest from land. Density was consis- 

 tently low in the northeastern portion of the 

 area. High density near the main Hawaiian 

 islands was a result of concentrations of sea 

 birds (primarily Sooty Terns, Brown Noddies, 

 and Wedge-tailed Shearwaters) on islets off the 

 main Hawaiian islands during the breeding sea- 

 son, March-November. High density at the 

 southern end was apparently due to the attrac- 

 tion of birds to an area where cooler, subsur- 

 face, food-rich water domes came close to the 

 surface. The estimated average total popula- 

 tion of all species on any day was: 466,320 

 birds in spring (March-May); 419,750 in sum- 

 mer (June-August); 410,640 in fall (September- 

 November); and 260,880 birds in winter (De- 

 cember-February). 



Taking into account the estimated number of 

 sea birds in the study area, their body weights, 

 and the percentage of their weights that they 

 consume daily, the birds consume 7,386.6 

 metric tons of fish, squid, and other marine 

 organisms annually. 



Sooty Tern was the most abundant species, 

 followed in order of decreasing abundance by 

 Wedge-tailed Shearwater, Sooty Shearwater, 

 Brown Noddy, Juan Fernandez Petrel, Leach's 

 Storm Petrel, Black-winged Petrel, and Slender- 

 billed Shearwater. 



Analysis of the direction of movement of sea 

 birds in the study area showed that almost all 

 direct migrants headed north or northwest in 

 the spring, and south or southeast in the fall. 

 Wintering species flew mainly west in the spring 

 and south in the fall. The direction of move- 

 ment of the main Hawaiian group was away 

 from breeding islands in the morning and to- 

 ward them in the evening. 



The relative abundance of sea birds at each 

 hour after sunrise and before sunset showed 

 that most species were more active in the early 

 morning or at noon, and again shortly before 

 sunset. As would be expected of birds that 

 scavenge behind ships regularly, albatrosses 



106 



