402 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



completely around. In two or three seconds it righted and began following 

 boat again. 



November 6, 2.30 p. m. — Ferry going west; fair wind from starboard. A 

 number of gulls soared over windward side, moving sidewise and forward, with 

 left wing advanced (pi. 4, figs. 1 and 2) ; that is, the birds were moving with the 

 boat, while facing a point halfway between the course of the boat and the 

 direction of the wind. 



3.40 p. m. — Ferry going east; wind from port. Birds soared as before, on 

 windward side, but with right wing advanced, as would be expected from 

 reversed direction of flight. 



Their method of soaring was carefully observed. They would rise in the 

 upward current at windward side until at a considerable height, then drift 

 forward and laterally, to right or left, with gradual loss of altitude, until 

 they circled back into the ascending current and rose again. Thus their flight 

 was a series of circlings in and out of the ascending column of air, with a 

 steady forward glide to keep pace with the boat. The wings were held nearly 

 motionless, and slightly flexed (pi. 1) to derive the maximum lifting power of 

 the wind. 



The chronological order of these excerpts has been intentionally 

 disturbed, in order that they may furnish illustrations respectively 

 of the following points : 



1. That gulls take advantage of the air currents deflected upward 

 from buildings, steamers, hillsides, etc., to indulge in soaring flight. 



2. That they have not been observed to soar in the absence of such 

 currents. 



3. That the most favorable conditions for soaring about a steamer 

 occur with a moderately brisk wind from the bow, or either side. 



4. That a very stiff wind is not favorable to soaring. 



5. That the " soarable " position varies with the direction and speed 

 of the wind, and the nature of the object causing the upward draft. 

 Thus, in a moderate wind from starboard, the gulls soared over the 

 windward side of the boat, while in a stiff breeze over the crest of Goat 

 Island they soared to the leeward of the island. It has been observed 

 also that, with increasing briskness of the wind about the ferryboats, 

 the soarable area tends to move more and more to the leeward. This 

 may explain the confusion which has existed upon the point (Han- 

 kin, 1913 % p. 253), some observers reporting that gulls soar on the 

 windward, others that they soar on the leeward side of steamers. 



In conclusion it should be stated that these data are not intended 

 to furnish an adequate explanation of soaring flight in general, but 

 only of that of the gulls as I have observed it. It is entirely possible 

 that, in the magnificent soaring of eagles and vultures, particularly 

 as seen in the tropics, other factors may enter. Conditions at a 

 height of 1 or 2 miles must be very different from what they are at 

 the relatively small heights to which gulls attain. 



But if, as some maintain, birds are able to soar in the absence of 

 any noticeable upward movement of the air, it is yet entirely pos- 



