150 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 
