My first reaction was composition, I am guessing it was cropped this way because the perch was less than ideal. I think the bird has been wonderfully caught, I think I would lift the darkest plumage a little bit.
Your bird looks excellent, smashing colours and pin sharp, I would also like to see a horizontal composition and a bit more space around the bird, after saying that I would love to have it just as it is.
I like the pose, details and colorful subject. Its easy to blow the blue cap on these guys. Composition wise I would of went horizontal. Nice image Stuart.