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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 32 



Actually the beat is not horizontal, but it is not far from it. It 

 is an approach toward hovering flight, and, as can be seen in Fig- 

 ure 15, hovering birds do use this nearly horizontal beat, at any rate 

 in calm weather. The body is tilted up at an angle which brings it 

 into nearly the same position with relation to the beating wings as 

 in normal flapping flight, thus doing away with the need for special 



Figure 15. — Humming birds hovei'ing. (From photographs.) 



joints and muscles. This typical attitude, assumed by all forms of 

 ducks (and indeed most other birds) when alighting in calm 

 weather, will be recalled by Figure 16. Incidentally this attitude 

 must in itself cause a certain increase in the braking efl'ect caused 

 by the passage of the body at an angle through the air, and must 

 also reduce the tendency to capsize on touching the water. 



j.„.r..i. .( mkr 



FiGDRB 16. — Left, typical attitude of a duck while alighting. 

 Right, diagram illustrating the action of a duck's wing in the 

 down or forward beat while alighting. The section of wing 

 shown is near the body. Farther out toward the wing-tip, the 

 air-stream would twist the wing so that the angle of incidence 

 would be smaller 



The slot comes in very handy in this proceeding, too. Imagine a 

 point on the teal's wing traveling, during the forward stroke, from 

 A to B (fig. 16) and producing a force from the reaction of the 

 air, roughly, in the required direction R. To do so, the surface of 

 the wing must lie at right angles to that direction, that is, in posi- 

 tion CD. The air stream felt by the wing during the stroke is, 

 practically speaking, in the reverse direction to the stroke, i. e., from 

 B to A (because the bodily forward movement of the bird is now 



