I totally agree with the others that cropping the black at the top out would seriously throw the composition and balance of the photo off, but still find that it distracts me! Never-the-less, it is still a stunning shot.
I too feel the dark band at the top is essential in providing a balance to the central dark band and the bird itself. Great use of space and colour - a very strong silhouette/ wildlife shot.
I like this composition a lot. It shows vastness inside a small frame. You don't see much of the surroundings but you are taken there. I think it would be worth trying to play with Curves a bit so see how it looks with slightly increased contrast and saturation.
I disagree with Linda. While it would be nice to have a row of trees in the background, that dark area does add some punch, and the crop is right where it should be. Cropping further would throw the balance off, and cloning more water above the bird would result in a blandly symmetrical composition. My only complaints are minor: the horizon isn't quite straight, and there appear to be some sharpening artifacts around the egret. This image would sell on DPCPrints.