Here is the completed saker falcon study
They seem to be rather diverse birds in terms of plumage. I found some with heavily streaked heads, and some with only a few streaks of brown. Of course, I know some of these birds may have had more immature plumage than others, but even the coloring on the back seemed different - some had slight barring, others didn't, some were more blue-gray and others almost entirely red. I think I got it for the most part, however, and it is good practice for my next thesis painting, which will explore the saker falcon in Middle Eastern falconry.
For this, I covered everything in the background wash (which I liberally textured with splatters from brushes and a toothbrush - lots of fun!), and then went in and painted the details on top. I also used a lot of white gouache, since I wanted parts to be more opaque.