Ed, I went back and looked at your owl shots here
Twin Great Horned Owl Chicks - Image Critiques / Avian Critiques - Nature Photographers Network
and the focus on the subject looked good so I doubt you are having front or back focus issue with your 100-400 IS II.
FWIW, for action shots with my 7D mark II, I almost always used the 15 center autofocus points as opposed to the single center point. This helped me keep the subject on an active focus point. This is assuming the scene wasn’t too cluttered and I could keep the focus points off anything in the foreground. This was especially helpful for birds in flight but I also used it for birds actively feeding on the beach.