The Lesser Yellowlegs is the bird at the bottom. The only reliable way to distinguish them from the Greater Yellowlegs (at the top) is to photograph them together. Today I got lucky. The smaller size and generally shorter bill are not always apparent when solo. Another distinguishing feature, which can be seen pretty well in the first photo, is the length of the primary wing feathers. Here, in the Lesser Yellowlegs, they can be seen to extend noticeably beyond the tail.