Good exposure and eye contact. These little guys aren't the easiest to catch in flight as they are pretty fast and skittish. I might lighten it over all just a tad and maybe a little more sharpening.
Nice catch of this speedy flier! I agree that cropping it a little differently could help with the composition...thus decentering the Killdeer and giving him more room to fly into the frame.
Other than already said, I like the texture of the sky, adds a lot to the composition.
I'm bit bothered by the warmer URH corner patch in the BG. I'd clone it away.