It looks as if this fly is tied from rear to front (like most flies) and utilizes clumps of gill material (the ostrich herl) that are tied in along the shank of the hook. After each clump is tied in using your thread and bobbin, then a turn is made of the white yarn bringing the yarn ahead of the herl. In other words, you tie the herl clumps individually, then palmer the white yarn forward, then tie the next herl clump; repeat until you get up to the front of the fly.