7. Get some pretty light or dark color - best of all, both, so you can make a little shadow as well - and draw in all the middle lines. My favorite brush for all those things is 'wet detail brush 5' from the acrylics, because it both blends and draws very small detail quite well. If you're using Photoshop or something else at this stage, DON'T EVEN THINK of only using dodge/burn lighten/darken tools! What you'll get will be rather monocrhomatic feathers, that won't look as interesting as they'd get if you use actual color. Check reference for where they are located for different types of feathers.
--Warning! The following part should only be done if you have no attachment to your wrist, because it may become very detached to the process.--