People often ask me to share the best ways to identify migrating warblers — especially in the East and Midwest where post-breeding plumages can sometimes create identification challenges.
My brief answer is that there’s no replacement for doing your homework in the field. Getting out early and often with your binoculars is the best way to see lots of warblers. The more challenging identification episodes you encounter, the faster you become precise with your warbler field skills.
One identification resource I recently found may interest you. It’s an online “chart” that’s found at: http://www.migrationresearch.org/mbo/id/fall_warblers.html
The author, Marcel Gahbauer, does a terrific job of separating 30 species of warblers by various key feather field marks: a) presence of wingbars or not; and b) facial, throat, and undertail characteristics.
Enjoy your autumn birding!