I like the open wings and position of the bird. I'm thinking a higher ISO would have allowed you to go to F/8 and get more DOF... but its sharp in the eye were it matters most.
Very nice light. I think that your aperture is probably the correct choice, because and more DOF would have brought the background more into focus, which I think would have been more of a problem than the slight blur of the wing. The eye, head and feet are sharp.
I agree with Axel about just a bit more room, top and bottom.
I think Kims point is valid as well about the background brightness, but it didn't strike me as distracting.
Thanks for sharing. I always chuckle at these guys. All bill, no legs! Obviously not a wading bird!
I like the picture. The 'just about to land' shows good timing. In particular, the Skimmer's bill. I always see these birds a long way off, or flying high. It is interesting to read the other postings regarding DOF and lighting. It goes to show what current thinking is at the moment. Again, good shot.