Table 8. — Sea bird densities in birds per 30 linear miles (55.6 km.) of observation at 

 various surface salinities in increments of 0.30 p.p.t. (parts per thousand). — Con. 



Species 



Period 



Salinity (p.p.t.) 



33.00 

 33.29 



33.30 

 33.59 



33.60 

 33.89 



33.90 

 3A.19 



34.20 

 34.49 



34.50 

 34.79 



34.80 

 35.09 



35.10 

 35.39 



35.40 

 35.69 



Number of birds 



Brown Noddy 



White Tern 



Spring 

 Summer 

 Fall 

 Winter 



Spring 

 Summer 

 Fall 

 Winter 



0.00 0.00 



0.00 0.18 



Number of environmental observations 



Total 



17 



69 



162 



321 



484 



405 



214 



18 



Table 9. — Monthly abundance and size of flocks 



Flock distribution . --Almost all months 

 showed two pronounced density centers--one 

 within 50 miles of the main Hawaiian islands 

 and the other at the southern end of the study 

 area, usually in the southeastern corner (fig. 

 35a-d). 



The density center near the Hawaiian Islands 

 was absent in November and December, and the 

 southern density center was lacking in May 

 1965 (but not May 1964, when it was probably 

 most pronounced). In addition, secondary den- 

 sity centers developed during some months, 

 usually in the area between the two main cen- 

 ters or at the northwestern corner. Only in 

 July 1964 were flocks of any size seen in the 

 northeastern corner. In all other months this 

 area was devoid of flocks, or nearly so. 



Flock composition . --Sooty Terns dominated 

 the composition of flocks in the study area in 

 all months except September 1964 (fig. 36). 

 Wedge-tailed Shearwaters were second most 

 abundant in flocks. These two species accounted 

 for over three-quarters of all birds in flocks. 

 Although both species were most abundant in 

 the main Hawaiian island area, both were well 

 represented in more pelagic flocks too, es- 

 pecially in the southern center of flock density. 

 Noddies and boobies were in the flocks near 



97 



