252 THE STRUCTURE AND LIFE OF BIRDS cHapP. 
others. The Swallow, like the Kestrel a first-rate 
steerer, comes second. The Duck, who turns in a long 
curve and with labour, has the stiffest waist of all. It 
seems probable that a bird alters his balance in order to 
change direction much asa skater does. Supposing 
that he is curving to the right on the outside edge 
on the right foot, the skater turns to the inside 
edge (on the same foot), and curves to the 
left by swinging the weight of his shoulders across. 
And this is done by contracting the muscles at the 
waist which lower the left shoulder. A bird may well 
change balance in a similar way, swinging his hind- 
quarters to right or left according to the direction 
in which he wishes to go, and beneath the feathers 
the process may not be visible to us. Certainly 
the head is often turned at the moment of wheeling, 
apparently to helpthe movement. Occasionally, how- 
ever, like a good skater who despises conspicuous helps 
to a change of equilibrium, such as a swing of the leg, 
a Gull may be seen looking to the right while he slowly 
turns to the left. It is these slow turns, when there is 
almost certainly no beat of the wings, and during which 
the head is occasionally turned the other way, that 
make me think a bird alters his balance by a bend at 
the waist as a skater does. In the more rapid turns 
there may well be a momentary unequal beat of the 
wings that defies detection. 
Stopping. Use of the Bastard Wing. 
When a Pigeon in mid-flight wishes suddenly to stop 
he alters the inclination of his body, which has been 
nearly horizontal, and, relaxing the muscles that had 
