This bird was amid a mixed flock of about 2,300 birds on the ocean side of Duxbury Beach about 100 yards north of the 2nd crossover in a protected area (for Piping Plovers and Least Terns). The photo doesn't convey how different this bird looked in real life but does show enough to indicate that it wasn't an ordinary Semipalmated Sandpiper... unless it had washed itself in some dirty water. The bird is more brownish than the Semis it was with and that shows somewhat in the photos.