I had over 180 Dowitchers at a nice location in Caruthersville, MO. All that I could see well enough or heard were Long-billed, as expected in October.

On these flying birds, notice that on all of them the lesser underwing coverts are unmarked, and contrast as a small white patch to the rest of the barred underwing. The 2nd bird looks to be uniform, but in the next photo I took you can see the underwing and it too has the same look. Short-billed tends to be uniform, with the lesser underwing coverts lightly barred as the rest of the underwing. For a comparison to Short-billed see: http://www.pbase.com/mctodd/image/112483054