Originally posted by dirwood I feel it can improve...
It's a nice shot, but I would suggest to leave a litlle bit more room around the bird, especially at its front (left and top sides). I would also add some slight vignette to bring the viewer's focus on the bird.
Contrast and detail are a bit low due to the weather conditions (and high ISO and heavy crop, and handheld at 450mm: many adverse factors), like you said. The only remedy I see to that is possibility to try a black and white version, where you could then push contrast further. I'm not 100% convinced it will work, but might be worth a try.