Table 9. --Number and distance of flocks sighted by various fishermen 



In addition to the weather conditions, the visibility of the bird flocks which we are using 

 as indicators greatly influenced our results. In the Hawaiian area the sea birds are mostly dark- 

 plumaged and difficult to see against the background of the water. This effect is noticeable from 

 the vessel but is minimized by observing from close to the water where the birds are seen 

 against the sky. On the other hand, the difficulty is so great when observing from the plane that 

 we saw bird flocks of different connposition than those seen from the vessel. Of, 15 flocks sighted 

 during the 6 flights, 11 consisted predominantly or solely of white boobies, while only 4 flocks 

 were of the dark-colored terns and shearwaters. Vessel scouting at nearly the same tinnes pro- 

 duced sightings of 39 bird flocks, of which only 1 was white boobies; 19 contained no white- 

 plumaged birds at all, while the remaining 19 contained a few white birds. We conclude that 

 many flocks of dark-colored birds were overlooked by the observers on the plane. 



This is surprising because it is easy to see individual flying fish from the plane at an 

 altitude of 1,000 feet or more. When they leave the water they attract attention by the glitter of 

 the sun on their wet bodies. However, they were not seen beyond about 1, 600 feet from the track 

 of the plane and most of them between 200 and 400 feet. During the last flight (Flight No. 6, 

 June 15, 1953, at 800 feet altitude) the angles from verticail were recorded for 152 objects sighted, 

 which were naostly flying fish and scattered birds. Tabulation showed that 52 percent were be- 

 tween 15 and 30 from vertical on both sides of the plane. Between (directly beneath the 

 plane) and 15 there were 17 percent, between 30 and 45 , 13 percent, and between 45 and 60 , 

 18 percent of the total sightings. The small percentage recorded directly below the plane was 

 probably a result of its being somewhat of a "blind spot" to the observers, who experienced some 

 difficulty in vertical scanning. Thus for objects of this kind the effective scanning radius of the 

 plane is only about 1/3 mile or less. Of course, large flocks of birds might be seen at greater 

 distances, but we saw so few that we have no estimate of how far they might be seen. 



15 



