In addition to Brad and Ed's digiscope shots, I was able to get some distant DSLR photos of the Wandering Tattler with a lot of work and experimentation, esp. during the great looks during the first 45 minutes or so.
Although a few supporting field marks are evident, the photos show a key field mark not mentioned in previous posts, so I thought I would chime in. Knowing that the separation of the two Tattler species is difficult at this distance, being without the unique vocalization or close looks at the leg and/or bill structure that can work in any plumage and age. Fortuitously, we realized our luck that this bird was mostly still in alternate plumage for the most part, being so early in migration season. We pinned hopes on getting photos that might possibly show differences in plumage often only seen in alternate plumage of such similar shorebirds.
In this case, the shots show extensive streaking all the way to the undertail coverts and only a small, but still allowable white patch near the vent (which some of us thought we were seeing in the scope views). This is mentioned as being diagnostic on Wandering Tattler in better reference guides (Shorebirds, Hayman, et. al.)