I saw this bird by itself, and mistakenly identified it as a juvenile Pectoral Sandpiper -- a good lesson in how easy it is to get size wrong on a bird seen alone. Here's another juvenile Least that I photographed nearby on the same outing, and correctly identified: http://www.pbase.com/tgrey/image/66314690 . They look pretty similar, huh? But I was able to keep talking myself into calling this one a Pectoral because of the striping on the upper breast, as compared to the brown wash on the other bird. Juvenile Pectorals usually have very pronounced striping, but the books say that in some cases it can be relatively faint, and I convinced myself this bird fell under that exception. Live and learn!

Here's a typical juvenile Pectoral Sandpiper, with the usual heavy striping: http://www.pbase.com/gtepke/image/23191476