SOOTY TERN 



SPRING 





SOOTY TERN 



SUMMER 



50 n 



23 24 25 26 



37 132 135 67 



SOOTY TERN 

 c<o FALL 

 C3 50t 



= 21 ' '21 

 



22 

 6 



24 

 57 



25 

 124 



WATER TEMPERATURE (°C) 



SOOTY TERN 



WINTER 



50 



WATER TEMPERATURE (°C) 



Figure 34. — Number of birds seen per 30 linear miles (55.6 km.) of observation at various water 

 temperatures in increments of 1° C. The number of samples in each increment is given below the 

 temperature . — Continued . 



migration. The numbers of migrants increased 

 the totals in these months and caused a de- 

 crease in the relative abundance of flocking 

 birds. 



The greatest numbers of birds in flocks were 

 in May of both years. Sooty Terns, Wedge- 

 tailed Shearwaters, and Brown Noddies feeding 

 in the main Hawaiian area accounted for the 

 large numbers. A high plateau was maintained 

 from June to September, and a second peak was 

 recorded in October. Numbers in flocks were 

 lowest inNovember and December, when breed- 

 ing activity was almost nil in the main Hawaiian 

 area. In November 1964 the number of birds in 

 flocks (925) was second lowest, and the mean 

 number per flock (27.2) was lowest for the 15 



months of the study. In December 1964 21 

 flocks had only 880 birds--the lowest monthly 

 total recorded. Birds in flocks increased in 

 January as Sooty Terns returned to the Hawai- 

 ian Islands and remained steady until May, 

 when numbers reached a peak again. 



Although the number of flocks observed in a 

 month was highest (100) in June 1965, the mean 

 number of birds per flock was low. In May of 

 both years 87 flocks were seen, and the mean 

 number of birds per flock in May 1965 (88.1) 

 was the highest average in any month. 



The largest single flock contained 955+300 

 birds. It was observed on May 31, 1965 about 

 50 miles north of Oahu. 



95 



