Khun Hans

Hello everyone! I am so happy to have found this forum which is sharing the beautiful passion for bird photography.
As an introduction: I am an amateur photographer, I have purchased my first Fujifilm this year (an XT-200) after over 11 years shooting with a compact Canon (G11). Since I live in Panama, and I love wildlife, I got more and more into bird watching and bird photographs, since I can find dozen of beautiful and colorful species in my backyard (besides many other wild animals).
I have just bought a 2nd hand XC 50-200 lens, which seems to do a great job for my needs (see the keel-billed toucan here below), I have been shooting only during daytime,  and mostly to birds in a standstill (i.e. not flying) with different light condition, and pretty much always in manual mode (M) with the following settings:
ISO set to AUTO2 (ISO base 200; ISO limit 1600) Photometry: Multi Shutter type: MS Focus  mode: AF-S AF mode: zone SS: I play around between 500 and 1000 F: I try to keep it as low as possible, but I don't play too much with this I am a bit overwhelmed with the amount of setting and option and still in the learning process of the new camera and the brand Fuji.
Now the question part: I have been trying to use S (shutter priority AE) mode and got completely confused. I have been trying to move across a big range of SS in good light, and F sets at 4.5 automatically but it is nearly always RED. I cannot get any decent photo in this mode. I am not very familiar in shooting in A mode either. But I would gladly hear from any of you who can provide suggestion on how to better take advantage of semi-automated mode(s).
Have fun!