Beautifully captured color and detail. I think they go after those small shelled animals that burrow into the sand when the wave retreats. Great shot!

I am not sure exactly what that thing in his mouth is, but I strongly suspect is some small crustacean that is burried in the sand, just below the water. All the sanderlings in the area appeared to be feeding on the same thing. Many of the shorebirds in the area (Herons, egrets, sandpipers, and dowitchers, etc.) appear to feed on similar items. The sands just below the surface of the water, especially at low tide near dawn and sunset seem to attract many of these birds for feeding.

Nice image - I like that he has something in his mouth.