396 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



under other circumstances, and it would be a mistake to assume that 

 modes and methods of flight adapted to some particular set of condi- 

 tions hold true for all. 



The writer became interested in some of these problems by watch- 

 ing the maneuvers of gulls about the ferryboats, and he began ac- 

 cordingly to take notes on their behavior with reference to the 

 speed and direction of the wind and other factors, as he had oc- 

 casion to cross the bay from time to time. The present paper is 

 based on a series of observations covering a period of about nine 

 months, from July, 1921, to March, 1922, during which time the 

 writer has on occasion laid himself open to suspicion of mental 

 aberration by rushing about on the deck of a ferryboat, gazing 

 seaward and skyward, and jotting down notes in a small black book. 



The machinery of flight — the structure of wings and feathers and 

 the nice musculature which controls them — has been dealt with in 

 much detail by Headley (1895 and 1912), Hankin (1913), and 

 others. It is sufficient here to note that the wings are strong, rigid, 

 and light, that they are curved to offer the maximum resistance on 

 the downward and the minimum on the upward stroke, and that 

 the great wing feathers, by their shape, contribute materially to 

 the action of the muscles and relieve unnecessary strain. It is gener- 

 ally agreed that the muscles and tendons of the wing are so arranged 

 as to operate automatically, the motion which extends the humerus 

 mechanically extending the other units of the wing, even to spread- 

 ing the flight feathers. (This view has been objected to by Beet- 

 ham, 1911, p. 435.) It is important also to note that the tips of the 

 flexible flight feathers bend upward under the strain of any sudden 

 gust (pi. 2, F) , thus allowing the wind to " slide off " from the under 

 surface of the wing and contributing automatically to the main- 

 tenance of equilibrium. 



Having in mind these few notes on the mechanics of flight, we 

 may go on to consider the bird in action, which has been the major 

 object of these studies. Nothing appears more leisurely and effort- 

 less than the flight of gulls. The exertion by which they keep pace 

 with a steamer seems to be little more than an idle flapping, when 

 indeed they are not soaring on almost motionless wings above the 

 boat. But when we come to study more closely just what is taking 

 place, and particularly when we record photographically certain 

 movements that are too quick for the eye, we discover that more 

 energy is being expended than at first seemed to be the case. 



The first point to be noticed is that the stroke of the wings is con- 

 siderably longer than appears to the eye; indeed, each time the pin- 

 ions are raised the inner segments almost meet above the body, and on 

 the downward beat the outer segments approach the perpendicular 

 beneath it. This can partially be seen when a bird passes directly on 



