298 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



the end of the downward and forward stroke of the beat. The back- 

 ward and upward stroke starts with an upward and backward move- 

 ment of the wrist joint, uncovering the head and leaving the primary 

 feathers directed forward along the line of flight (photograph 8). 

 Then the primary feathers are drawn violently backward and upward 

 (photographs 9-11) and the whole wing straightens out in position 

 for a new downward movement. 



These same phases of a complete wing beat can also be seen from 

 another direction in plates 7 and 8, where the pigeon is flying across 

 the field of the camera ; photographs 1-6 show the downward and for- 

 ward stroke, and photographs 7-12 show the upward and back- 

 ward stroke. Photographs 2-4 show the separation and bending of 

 the primary feathers during the first moments of the downstroke, and 

 the forward swing of the whole wing is seen in photograph 6. The 

 raising of the wrist and the subsequent very rapid backward flick of 

 the wrist and primary feathers are seen in photographs 8-11. From 

 these photographs it is possible to draw three conclusions with fair 

 certainty : (1) During the initial downward wing movement the wing 

 surfaces are traveling down in a direction almost perpendicular to 

 their path of motion, and consequently elicit a powerful upward re- 

 action from the air. (2) During the second part of the downstroke 

 the wing is traveling forward with its surface inclined to the patli 

 of motion at a relatively small angle; it thus acts as an airfoil and 

 develops a lift, in the normal way. (3) The main propulsive thrust 

 comes from the rapid backward movement of the primary feathers, 

 which occurs during the upward stroke. Supposing this analysis to 

 be true, it may be said that the downstroke of the wing gives the lift 

 and the upstroke produces both lift and forward thrust. 



But can a bird's wing do so much, and do it constantly, without 

 getting tired ? The downstroke is easy, for the wing is pulled down- 

 ward by the very large pectoralis major muscle ; but the muscles that 

 move the wrist and raise the wing are small by comparison, and it is 

 difficult to see how a very rapid series of upstrokes could be kept up. 

 And, in fact, it cannot. The photographs shown in plates 5-8 were 

 taken during slow short flights of about 20 feet, and it soon appeared 

 that pigeons find such flights tiring; 8 or 9 flights left this bird dis- 

 inclined to take further part in the experiment. It seems likely, there- 

 fore, that the wing movements observed during and immediately after 

 a takeoff from the ground are not the same as those of a pigeon in full 

 sustained flight in the open air, for we know that such birds can in 

 fact travel for a long time without showing fatigue. Dr. E. H. 

 J. Brown, therefore, decided to photograph the bird in full flight down 

 a long corridor. A series of such photographs is seen in plates 9 and 

 10. Two main changes are to be noticed in the downstroke: (1) the 

 amplitude of the beat is smaller — the wings no longer rise high enough 



