Wedge-tailed Shearwater 

 Puffinus pacificus (Gmelin) 



Status : Abundant resident during breeding sea- 

 son, March-November; common or uncommon 

 December- February. 



Total birds 



Dark-phase only 



Wedge-tailed Shearwaters were in the study 

 area all year but were scarce in winter. From 

 the yearly low in February, numbers increased 

 to a peak in May and June, roughly coincident 

 with egg laying on the breeding grounds on 

 islets of the main Hawaiian Islands, and along 

 the leeward Hawaiian chain. Numbers remained 

 high through September (the total for September 



in the above table was inflated by one sighting 

 of 700 birds a few miles from Oahu) but began 

 to drop off in October, somewhat before chicks 

 fledged on the breeding grounds. By February 

 only a few stragglers remained. 



At least two populations were represented in 

 the study area; in most months a fairly sharp 

 line of division existed between the light-phase 

 birds of the Hawaiian group and the dark-phase 

 birds from the southern islands (figs, lla-d). 



Distribution : A recurring density center of 

 light-phase birds was located within 50 miles 

 of the Hawaiian Islands during the breeding 

 season and somewhat later (April-November). 

 The rest of the study area, excluding the area 

 occupied by dark-phase birds, maintained a 

 fairly homogeneous density, bespeaking a ran- 

 dom distribution (exception: May 1964, in 

 which a large secondary density center devel- 

 oped at lat. 14° N., long. 151° W.). 



The range of dark-phase birds was confined 

 to the southern end of the area from March to 

 May, shifting north to lat. 15° N' in June and to 

 lat. 20° N. in July. Thereafter the range con- 

 tracted back toward lat. 10° N. In all months 

 the density center was at the southern end of 

 the study area. The range of dark-phase birds 

 covered the greatest area in July. We collected 

 one dark-phase bird. 



The light-phase birds represented a breeding 

 population (one bird collected at sea July 4, 

 1964 at lat. 23° N., long. 157° W. had been 

 banded in May 1964 on an islet off the coast of 

 Oahu) and were much reduced in numbers dur- 

 ing the nonbreeding season; the dark-phase 

 birds represented a wintering population (fig. 

 12). They were most plentiful in May in the 

 beginning of their nonbreeding season. It is not 

 possible to indicate the island(s) of origin of 

 the dark-phase population since several island 

 groups would qualify if we assume a large- 

 scale migration of dark-phase birds similar to 

 that of light-phase birds, which move at least 

 500 or 1,000 miles (925 or 1,850 km.) from 

 their breeding islands. 



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