This bird was observed at Crescent Beach (south-facing beach on the Saquish portion of Duxbury Beach - actually in Plymouth, MA). It was in a flock of Semipalmated Sandpipers behaving just like its peers - but its color made it stick out. Because the back is brown at first I though it was a Least Sandpiper but on closer look (black legs, bill, and general gizz relative to nearby Leasts)concluded that it was an aberrant Semipalmated. I do not know what causes ths. Some have speculated that it must have "gotten into something" but that didn't seem to compute given the even nature of the coloring and the brownness of the back/wings. (Postscript: An identical bird (must be the same one!) was seen in the same spot 2 years later (7/20/13 vs 7/21/11). This suggests that the color is part of the bird itself.