I'm probably the last person to ask for an ID, but looks like a classic Dusky Warbler.
There are 2 confusion species (things that look a lot like this), the less common Radde's Warbler and the one or so a year on migration Yellow-Streaked Warbler. Usually they are IDd by how common they are and call.
The guidebooks focus on the "eyebrow" (supercillium), which in your bird's case shows the classic more white in front of the eye and a bit creamier behind the eye.
You'd have to ask the ringers and the folks who own the new ringing book about my second ID point. I haven't looked at Radde's Warbler wings to see if there is a difference, but Dusky Warbler look to have primaries (the group of long feathers to the outside of the wing) which are shorter than the secondaries (the group of long feathers above the the primaries) and your bird fits this perfectly.
