I recently found an article by Cin-Ty Lee and Andrew Birch titled "New advances in the field identification of dowitchers". They have figured out a few details that can really help nail down a silent dowitcher, or at least get you most of the way there. How I missed this article before is beyond me (don't judge).
The identification tip I liked most was the pattern of the greater and median coverts in alternate plumage; squared off white in Long-billed Dowitcher while the white extends up the side of the feather in Short-billed. Sure wish I knew about this feature a long time ago!
Just so happens that some of the Dowitchers here in Florida are molting. On 3/31 I photographed this Short-billed Dowitcher at Bald Point State Park. It was part of a flock, and the birds were calling. I didn't get the call recorded, but luckily the covert pattern tells all.
|Molting Short-billed Dowitcher|
|Short-billed Dowitcher covert pattern with white extending up the sides of the coverts (not squared at the tip like in Long-billed Dowitcher).|