Baird's Sandpiper (Calidris bairdii)

Obviously intermediate in size between Pectorals and the small peeps. Black legs and (slender) bills. Wingtips projected beyond tail. Pale buff breast and face (with dusky cheek patch); large dark spots on mantle; clear white flanks. Dark rump seen in displays where they raised wings and charged each other. Perfect -- suddenly everything just came together.