drake crash-landing with back to wind give eloquent testimony to the im- 

 portance of obeying the fundamental rules of aerial maneuver. 



Once airborne, all physical contact with the earth is lost and the bird 

 no longer has any bodily sensation of the speed or direction of the wind. An 

 awareness of the air flow depends on a visual reference to the earth. In 

 short, the bird, like the human pilot, must appraise the speed and direction 

 of the air mass in which it travels by perceiving the relation between its 

 own movement and the earth below. The duck turning upwind to a gun- 

 ner's rig sets its course, not by feeling the wind, but by obeying visual cues 

 it perceives in the marsh below. 



This problem of wind-perception by flying birds has been a matter of 

 considerable confusion for many groundling ornithologists who believe that 

 the bird is sensitive to the wind pressure as this may be felt or the feathers 

 ruffled on the windward side of the body. Lewis (1939b: 22) explains that 

 once the bird is on the wing it is "supported by the stream of air surrounding 

 it and has no solid attachment to anything. It cannot then apprehend the 

 direction of the wind by any pressure of the latter against its body, for, aside 

 from the possible effect of turbulence, the air pressure against its body 

 would be the same on all sides if the bird allowed itself to be swept along 

 as an inert object in the air current. By^its own efforts in flying ahead 

 through the surrounding air, the bird causes increased pressure against its 

 forward side, but this result is obtained indifferently and to the same extent 

 whether the bird directs its flight with, or against, or across a uniform 

 stream of air. Except under unusual circumstances, the flying bird therefore 

 presumably has no awareness of the direction or the velocity of the wind or 

 of the direction or velocity of its own movement in relation to the surface 

 of the earth or in relation to the direction or velocity of the wind unless it 

 can perceive some fixed points on the earth or, for knowledge of direction but 



56 



