I like the pose of the bird, nice reflection. The whites on the bird look quite gray, so I think the image could go a bit brighter. 230 is a nice number for whites.
The head is a little soft (not sharp). The tail looks a bit sharper, so perhaps your focus point was off a bit.
I know it sounds funny to say the sand is too grainy, but there seems to be some digital noise in the image, a little surprising at this ISO. Did you need to bring the exposure up in post processing?
You have a lovely-looking bird here, Gavin, with a nice head angle and catch light. Good assessment by Randy. I would also note that your horizon is off by a little. The way you can tell in this image is that your beak should be in exact alignment with its reflection. If this were mine, I would crop it from the bottom. I have attached a version with a straightened horizon, with some crop and I sharpened the head a little bit. I think this comp, by minimizing the power of your rocks, works better to show off your bird.
The bird is nice and sharp, but the angle is a bit high. Could you have got a bit lower? Also, there seems to be a bluish-green cast to the whole picture, especially the sand. I prefer Marina's crop.