10. Stercorariidae 



Two species of jaegers and one skua 

 were recorded. The jaegers breed in the 

 Arctic and migrate south, the skua breeds in 

 the South Pacific and migrates north. Only 

 thePomarine Jaeger was observed regularly. 



11. Laridae 



Two or possibly three species of gulls 

 and seven species of terns were recorded. 

 The gulls were all stragglers from the North 

 Pacific. One tern was a migrant on its way 

 north to the Arctic in the spring. The islands 

 of origin of the three species of tropical 

 terns are in doubt, but the three species of 

 noddy terns were observed almost entirely 

 within 100 miles of the Hawaiian Islands. 

 The tropical terns evidently migrate season- 

 ally, but the noddies remain resident all 

 year. The Sooty Tern was the most abundant 

 species in the study area. 



12. Columbidae 



One Rock Dove was observed 10 miles 

 (18.5 km.) from Oahu where the species 

 breeds abundantly. 



Diversity of Species 



Forty-nine species and two field-recognizable 

 subspecies were observed in the study area. 

 The number recorded per month ranged from 

 32 (April 1965) to 17 (July 1964). The monthly 



average was 24.2 species. The number of 

 species observed on any day ranged from 2 to 

 15 (mean 7.7). Numbers were usually highest 

 within 50 miles (92.7 km.) of Oahu and lowest 

 in the northeast corner of the area. Accidentals 

 and stragglers caused the species-per-month 

 figures to be higher, and more erratic, than the 

 species-per-day figures. 



Only a weak positive correlation existed be- 

 tween numbers of species and total numbers of 

 birds per month. During migration months 

 (April and May, October and November), when 

 total numbers were highest, species diversity 

 was also high (fig. 2). Species diversity was 

 lowest during the summer (June-September), 

 owing to the low frequency of migrants and ac- 

 cidentals, although numbers of birds were fair- 

 ly high. The high diversity of species during 

 the winter (December-February) compared with 

 total numbers of birds can be accounted for by 

 the higher incidence of accidentals at that time 

 of year. 



Species Accounts 



Fifty-one species or field-recognizable sub- 

 species were observed in the study area, and 

 accounts have been prepared for each. The 

 species accounts give first a general statement 

 of the status of each species and stress the 

 time of year that status changes occurred. The 

 species accounts also give a tabulation of the 

 numbers recorded on each cruise. All birds 



36-, 



30 



l^v 



18 



12 







Species per month 

 -Birds per hour 

 ■Species per day 



-•^. 



Mar. Apr May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb Mar. Apr May June 

 1964 1965 



Figure 2. — Numbers of species observed per day and per month and numbers of birds 

 per hour in the study area, March 1964 to June 1965. 



