I originally posted this as a Semipalmated Sandpiper, having seen it with another birder who identified it as such when seen, not thinking it was big enough to be a Baird's when I saw it, and not being persuaded otherwise when I looked at my pictures and checked my books. But as observers pointed out, the primary extension well beyond the tail tip is plainly visible here. The bill is also arguably more long and thin (like Baird's) and not enough short and blunt-tipped (like Semipalmated.)The breast also has more buff than would be normal in Semipalmated.