Jay,
Beautiful light and subject as well.
I like the water rolling off the GBH beak.
You have more negative space in front of the bird than behind and that is good.
I would prefer to see more room at the top. With this type of image I'll put the horizontal line right in the middle, so the bird and reflection are of equal size in the frame.
You know a mirror look.
Very nice light, and good head angle. I agree a bit more room at the top would help the image, and you might want to remove the small black spot above the head near the upper border. I don't know if just a bit more USM would help; the area around the eye seems just a little soft on my monitor, but that may be the choice of focus point.
I agree with both James and Bill. One great thing to add to your post-processing routine is to enlarge all images to 75-100% and go down the entire image looking for dark and light spots - especially when there's water involved. These will show up as some ugly spots if you choose to print it so clone out that one dark spot and I'd add the small white area right below his body next to his legs.