436 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1911. 



doubt have revealed the wings as fully extended as in figure 2. 1 

 Here the wings are just beginning to feel the weight of what they are 

 to support and are commencing their first downward beat. And 

 now, though it has only traveled a few inches from the rock and the 

 feet have not yet been tucked away under the tail, the gannet is 

 fairly on the wing, exasperatingly able and wishful to go beyond the 

 range of our lens or even of our observation. 



II. STEERING, SLOWING-UP, AND TURNING. 



The old idea that the wings of a bird simply flap up and down, and 

 that by some means the body travels steadily along on a level hori- 

 zontal course, has long been dispensed with. It is, however, difficult 

 to realize, but none the less true, that at each full wing beat the body 

 is raised as well as propelled. Perhaps this can be more readily 

 appreciated by reference to a photograph, such as that represented 

 in plate 3, figure 2. By good fortune the two gannets shown there so 

 near together exhibit the two extremes of the positions which these 

 birds .ordinarily assume in flight. In the top left-hand bird the wings 

 are raised and the body seems to be dependent from them, while in 

 the lower bird the wings are far depressed and the body appears 

 pushed up and supported by them; and this is precisely its position. 

 The wings in their rapid descent found resistance in the air, and as 

 soon as this resistance exceeded the force of gravity acting on the 

 bird the body was elevated at the same time that it was driven 

 forward, only, of course, to sink once again on the wings being raised. 

 Thus the path of a flying bird is a succession of ups and downs, but 

 the movements of the wings being so very much greater in extent 

 cloak those of the body, and so gracefully and smoothly are the 

 actions performed that we do not realize the undulatory nature of 

 the course. The attitude of the right-hand top bird, a kittiwake, in 

 the same photograph (pi. 3, fig. 2), is interesting, as it shows the bird 

 steering by the aid of its feet. The very extensive use some birds 

 make of their feet during flight requires consideration. Not only are 

 they freely used for steering, but they are also often employed as 

 brakes to lessen speed, much in the same way as a drag is used to take 

 way off an incoming vessel. In plate 4, figure 1, the immature 

 gannet there depicted is trailing its partly expanded and lowered 

 feet, thereby causing considerable resistance to its forward progress. 

 To birds which quarter the surface of the ocean for a livelihood, feet 

 have yet another use during flight. As the bird swoops downward to 

 snatch its swimming prey the legs are dropped, and the moment the 

 quarry has been seized, if not before, the feet are plied vigorously to 

 run along the surface of the water and thus not only act as buffers and 



1 The tip of the left wing of the bird in this figure has been retouched, as owing to an accident a portion of 

 the photograph (involving about half of the primaries) had become obliterated. The other photographs 

 have not been retouched in any way and have been chosen to illustrate the various points discussed rather 

 than because they were good photographs. 



