This gorgeous creature must have been pretty close to you with a full frame camera and a 300. You are a lucky man.
Exposure looks great. I think I would like to see some off of the bottom (up to just above that white line) and some off the left to bring it in a little tighter. This would bring more focus onto the bird. If there were more environment to include, I would go for the wider crop. In this case, I find the white "line" in the front just a tad distracting.
Now I'll have to go down and see your other post of this bird.
Looks very similar to the crop I gave it myself, except I gave it a smigeon more on the right. I feel this crop better showcases the bird...and what a gorgeous creature it is!