160 THE FLIGHT OF BIRDS 



revolves, he faces north, west, south, east in turn, 

 or vice versa ; and, as he turns, the inner wing will 

 always be rather lower than the outer one — this is 

 with all birds the commonest way of steering. 

 How he changes his balance is not quite clear. He 

 may, holding his wings rigidly in a straight line, 

 pull his body towards one wing or the other, and so 

 weight one side more heavily than the other. More 

 probably he bends sideways at the waist, as birds 

 certainly do for balancing and steering purposes 

 (see p. 60). Whatever the method, he has to execute 

 slow, swaying movements with the utmost skill. 

 Only when he travels straight for a bit will the two 

 wings be on the same level. There is no reason why 

 he should be in difficulties at all when the wind 

 strikes him on the side. It will support him which- 

 ever way his head points. A glance at the frontis- 

 piece will help to make matters clear. Though the 

 wings are held rigid, they are seldom horizontal for 

 long together. The spiral movement demands a 

 continual swaying of the body ; for the correct 

 incline, not only fore and aft, but also from left to 

 right, has to be maintained. The tail is frequently 

 at work, and this is probably accompanied by the 

 other movements I have just described. Otherwise 

 the body would not swing round promptly ; the bird 

 would not be able to describe his airy spirals. Fre- 

 quently the wings are held slanting throughout the 

 " circle," the inner wing pointing downwards to the 

 centre and seeming to act as a pivot on which the 

 bird revolves. But this is not always the case. 

 Sometimes a bird will put in a considerable bit of 

 straight-ahead travelling, gaining, maintaining or 



