This was done in max by Paul Hormis, I think. I am trying to figure out how it was done... The feathers are attached to the geometry, similiar to a rivet. When it bends it already gives pretty good spread. But there seems to be some additional control, like the feathers are aim constrained to the purple spline. And the whole movement is curvy and smooth so there must be more to it.
Here are my thoughts:
I created bones at the back of the wing, moving along with the front bones. A spline is bound to these bones (similiar to the purple spline) This spline has the ability to detach from the bones and could then serve as a wire deformer for the feather. The problem is, the clusters I used to deform this spline would go haywire and move in unpredictable ways (transform along world up would move them somewhere else). Also the feathers were squashed a bit too much, they should bend up and down but not sideways.
The purple spline could be done as a stretchy bone curve with the bones serving as aim targets for the feathers. But this would be a pain to set up I think.
The rig looks so simple and efficient. I've got the feeling I am making this more complicated than necessary so if anybody can think of ways to rig this up in Maya it would be much appreciated!