From Hertel, Fig 54 Effect of alula
Steep angle of attack alpha = 33 deg
 Above: separated airfoil flow at alpha = 28 deg
 Below: unseparated flow with bastard wing at alpha =33 deg
 
(Figure 2b), From Kuethe
 The thumb pinion is a clump of small feathers at the leading edge of the wing. Serving as a leading-edge flap  At the wrist of the wing, it twists to direct parts of the lift in the forward direction
 
 (Figure 2c), From Kuethe
 The split-flap configuration, formed by the wing of the gull in landing, generates both high lift and high drag.
 
 (Figure 2d), From Kuethe
The Kruger Flap is formed by the tuft of feathers that projects downward along leading edge of a sparrow hawk's wing, the bird forms an aileron-the device which (basic to all bird flights) acts differentially to provide lateral balance.
 
 (Figure 2e), From Kuethe
 The Fowler Flap is formed by the tail of the split-tail falcon. Swinging into position behind the wing, the two halves of the tail act as aspirators which accelerate the flow near the trailing edge. As a result, the stall is delayed with no significant addition to the drag.

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