A distribution wrap allows you to both distribute fibers evenly around the hook shank and shorten long fibers if desired.
Get hold of the feather’s very tip, here mallard flank-dyed wood duck. Pull the lower fibers down so you can snip the tip off. The feather should end up looking like this, with the tips relatively even on both sides. Place one set of fibers against the near side of the hook so they’re the appropriate length. Keep the fibers spread out, like so. Taking a wrap of thread will distribute the fibers over the entire near side of the hook.
Do the same thing with the fibers on the other side of the feather, on the far side of the hook. Ideally, these fibers should be the same length as those on the near side and should be evenly distributed on the far side of the hook. Now, the fibers should completely encircle the hook shank.
The distribution wrap is particularly useful for flies that are tied in the round, like Cal Bird’s Birds Nest. It’s a great technique to have in your arsenal.