The two dynamic curves are being driven by flex and drive all the feathers. This simplifies the dynamics solve down to just control points for the spines. From those the motion up and down only on the dynamic curves are being calculated and then applied to each feather. This stops the feathers from being stretched as the character moves quicky forward.
Final image from the commercial spot.
In the wire frame you we can see how simple the geometry is for the main feathers. More feathers were added but in sheets and just skin wrapped to the more complex ones. This was done for filler and again to simplify the need for rigging all the needed feathers.