page 1 2 3 4 5 - wing animation - MAYA TUTORAL 1 
To achieve a basic wing cycle, firstly the shoulder joint was rotated to its maximum and minimum settings and set driven keys were created on another custom attribute (WING_CYCLE). The second image below shows the graph editor with tangents being adjusted to make for realistic timing of the up and down strokes. 
The elbow joint of a bird moves in one plane only so rounding of the wing was achieved by a combination of deformers. First off, simple sculpt deformers were set up - one below and one above the wing - and these were parented to to shoulder joint so that they maintained a constant positional relationship to the feathers. Then they were carefully placed to achieve the correct deformation on the feathers for up and down strokes. Careful attention was paid to the surfaces to ensure that feathers were not pushed through one another, but maintained their proper stacked orientation over one annother. In order to achieve this, only minimal diplacement values were set - these were again keyed at 0 through to 0.8 under the WING_CYCLE driver of my central control null. 
Above, on the up-stroke, the top deformer's exerts no effect but the bottom sculpt sphere has reached its maximum displacement setting. The curves on the set driven keys had to adjusted by trial and error to effect a convincing hand over between up bulge and the down bulge. 
click here for page 5 of the tutorial