[SBB] Salt Pond A2E and New Chicago Marsh

This morning Frank Vanslager and I had two adult LEAST TERNS on the boardwalk in Salt Pond A2E. Later as we walked the railroad tracks thru New Chicago Marsh we saw eight RED-NECKED PHALAROPES (one in basic plumage) and two groups of WILSON'S PHALAROPES (24 birds in the larger group). Near the junction of the track with the track that runs thru Alviso we had eleven LEAST SANDPIPERS in one pond and three SNOWY PLOVERS (all juveniles?) in the dry impoundment between the railroad tracks and the dike on the eastern edge of Salt Pond A12. Unfortunately one short-billed reddish-headed sandpiper with a fairly dark lower breast? (extending to about the legs) and with white undertail coverts that was feeding on the ground in the middle of the marsh east of the RR tracks finally was finally lost from view and went un-identified. The bird had a somewhat long-winged look, was somewhat larger than a nearby Least Sandpiper and was first seen walking low along the ground as it fed. It always fed along the ground and at one point spent several minutes preening its lower chest (to remove a stain?). My beat guess is that it might have been a breeding plumaged Sanderling with a stained lower breast (primarily based on its size, head coloring, short straight bill and feeding habits (ignoring the dark lower breast).