POSITIONS ASSUMED BY BIRDS IN FLIGHT. 201 



when flight is being executed amid tumultuous currents. 

 But this method of steering by the tail is rather corrective 

 than initiative in its use, being principally employed 

 to compensate for irregularities in the air-currents. WHien 

 a bird is suddenly and deliberately changing the direc- 

 tion of its course — turning an aerial corner, so to speak — ■ 

 the plane of the wings is changed from the horizontal 

 position assumed when gliding to a more or less vertical 

 position, the inclination depending on the abruptness 

 of the turn and the pace at which it is executed. If the 

 burn is to the right, then the left wing is raised and the 



FIGURE 4. — THE DEPRESSED TAIL USED AS A BRAKE. 



[Photographed by Bentley Beetham). 



right depressed, and, of course, vice versa for a turn to the 

 left. When writing here of one wing being raised and the 

 other depressed, I refer to their positions relative to each 

 other, and not to their relation with the body. That is 

 to say, the wings and body may be held rigidly in one plane, 

 the inclination of this as a whole being changed from the 

 horizontal to towards the vertical. This vertical position 

 has been almost reached by the bird, of which, unfor- 

 tunately, only a portion is shown, in the upper part of 

 Figure 5. It will be noticed that the left wing is depressed 



