The most obvious differ- 

 ence in the composition of the 

 bird flocks in our scouting area 

 was the presence of boobies 

 ( Sula dactylatra ) close to land. 

 In our scouting in April Jind June 

 1953 (table 2) none were found 

 in area IV or the southern part 

 of area II, both of which are 

 beyond 100 miles from land. 

 White terns may be more abun- 

 dant farther from land, but the 

 nunnbers seen were too small to 

 be importaxit. The other prin- 

 cipal group8--terns, shear- 

 waters, and frigate birds-- 

 appear in the flocks without 

 regard to the distance from 

 lEind in our scouting area. 



The terns are believed 

 by the fishermen to be the most 

 important species as they are 

 considered to be the "leaders" 

 of the flock; their movements 

 closely paralleling those of the 

 fish. The captain of a fishing 

 boat generally observes the 

 behavior of the terns in order 

 to intercept the head of the 

 school successfully. 



Bird behavior is thought 

 to give a generally reliable indi- 

 cation of whether a school is 

 composed of tunas or of dolphin 

 (mahimahi), the number in the 

 school, and the size of the fish. 

 Birds which alternately fly very 

 high, then low, diving alnnost vertically to the surface and then rising just as steeply to great 

 heights, continuing this behavior, suggest--to the fishermen--the presence of a dolphin (mahi- 

 nnahi; school. This behavior appears to be independent of the species of birds involved, as terns, 

 shearwaters, and boobies all show it. Other behavior suggests tuna schools, the great majority 

 of which, in Hawaiian waters, are skipjack with only occasionalyellowfin, bigeye, or little tuna 

 schools. The size of the fish in a school may also be indicated by birds, for they are thought to 

 dive and circle faster and nnore erratically over snnall fish, perhaps because the small tuna have 

 a shorter turning radius. 



The size of the fish schools is judged by the spread of the bird flock rather than by the 

 number of birds involved. A small school is expected with a compact group of birds. A flock 

 scattered over a large area or broken up to form several smaller groups near each other sug- 

 gests a large school. In Japanese waters. . . "as a rule the size of the fish school is thought to 

 be proportional to the number of accompanying birdsj the greater the nunnber of fish, the larger 

 the flock" (Cleaver and Shimada 1950). 



A high-flying flock is believed to indicate a fast-nnoving school which is not actively 

 feeding at the surface. An actively feeding school is characterized by "working" birds which 

 are seen continuously diving in annongst the fish. (Fishermen often forgo schools with inactive 

 high-flying birds without nnaking any attempt to fish thenn, and select schools with "working" 



Figure 4. --Tracks of airplane scouting flights. 



