FLIGHT OF SEA GULLS MILLER 



401 



these depends upon ascending currents, but rather upon some mys- 

 terious transfer of sun (pp. 98, 105, 206) or wind (pp. 278 ff.) 

 " energy " to the soaring bird. Such a theory can hardly be looked 

 upon as doing aught but removing the phenomenon from the realm 

 of possible explanation to that of pure mystery. 



It seems at present that the earliest and simplest of these theories, 

 that of ascending currents, is the most plausible. So far as the 

 writer has been able to observe, it is entirely adequate to explain 

 the soaring of gulls. The following extracts from my notes will 

 indicate the basis of this statement : 



August 17, 2.20 p. m. — Clear, bright day ; stiff west wind. Several gulls ob- 

 served sporting in current of air deflected upward by ferry slip at Oakland 

 Mole. Would glide west some yards on motionless 

 wings, gradually losing altitude, then rotate wings so as * 



to be caught by breeze and swept back into ascending 

 current, in which they would speedily rise with no 

 visible effort and repeat the performance. This con- 

 tinued about five minutes, until birds were disturbed 

 by coming of a boat. 



August 13, 5.30 p. m. — Stiff west wind; several 

 gulls soaring a few yards above and slightly to the 

 leeward of the highest point on Goat Island. 



July 29, 10.50 a. m. — Ferry traveling against stiff 

 west wind. Gulls observed at points S, XX, and Y 

 (fig. 2). Those at XX flapped continually. Those at Y 

 took a zig-zag course, alternately flapping and sailing; 

 they would gain momentum by flapping vigorously 

 while in the shelter of the stern, then dive to one side 

 into the wind and sail a moment, quickly losing mo- 

 mentum but gaining altitude. Then, from this increased 

 height, they would dive back into the shelter of the 

 stern, usually adding to their momentum by flapping, 

 and continued across into the wind on the other side, 

 where they would again gain altitude with the loss 

 of momentum. This was repeated indefinitely, like 

 a sort of play. 



Several gulls were soaring without effort just above the forward pilot 

 house. There was scarcely a visible wing movement so long as they re- 

 mained in the area S (upward draft from bow), but they had to. resort to 

 flapping whenever they drifted to one side or the other of this area. (On 

 several occasions a gull has been observed very distinctly to fall off this up- 

 ward current, and drop suddenly somewhat laterally for 10 or 15 feet before 

 righting itself. 



July 30, 11.40 a. m. — Ferry going west against light breeze. Three gulls 

 soared smoothly just above forward pilot house, balancing by occasional flick 

 of wing tips. 



7.30 p. m.— Ferry going east, with light wind from stern. Several gulls fol- 

 lowed, flapping, at a distance. No soaring was attempted. 



August 1, 3.20 p. m.— Ferry going west against very stiff wind. Very little 

 soaring attempted, and only for a few moments at a time. One bird, alternately 

 flapping and sailing, was caught by a sudden gust, almost capsized, and turned 



Fig. 2. — Diagram of po- 

 sitions of gulls about 

 a ferry boat moving 

 against the wind 



