The most distinctive feature of dowitchers is their long bill. Godwits also have extremely long bills but their bills are bicolored and they are larger. In flight, dowitchers can be picked out of mixed shorebird flocks by the white "v" extending up the back. The Long-billed Dowitcher is very similar to the Short-billed Dowitcher. In alternate plumage, the Long-billed Dowitcher has barred flanks and a reddish belly; some races of the Short-billed Dowitcher have barred flanks and some have reddish bellies but not on the same bird. Juvenile Short-billed Dowithchers have a more orange plumage than juvenile Long-billed Dowithcers. The best field mark for separating the juvenile plumages is the appearance of the tertials. In the Short-billed they have internal orange stripes while in the Long-billed they have a thin brown fringe with no internal markings. Winter plumage dowitchers are very similar.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.