One is to clean the fluff from the stem and tie it in at the stem and wrap like any feather.

Another is to strip the fibers off the tip, tie it in at the bare tip and then wrap using the stem.

Another, used for over-sized feathers is to clip the top of the stem as he did and then face the remaining fibers to the rear and spin the feather around the hook using the thread to distribute the material around the hook.