Photographic Composition

The rule of thirds is effective in this photograph as each third has something different happening in it. The bottom third has the tide and the bird in it as well as the Sun's reflection off the water which creates light and shade.
The middle third shows the Sun which gives light to the photo and creates the shadowed look of the bird in the bottom third.
The top third is the sky which has became dark as the sun is setting. This creates light and shade as the bright sun contrasts with the darkening sky.