Tie in 3-4 microfibbets as a split tail about one shank long, splayed into a wide V for flotation.
Dub a slim, tapered abdomen forward to the 65% mark.
To build the dense 'puff,' gather the tips of a single CDC feather, fold them back on themselves, and tie the doubled clump in upright at 65%. Folding one feather gives a full wing without bulk at the base.
Stand the wing up with a few thread turns around its base.
Dub a small thorax fore and aft of the wing.
Whip finish, add a pinhead of cement at the head, and trim the wing to about one shank tall.