The Empid complexity.

In my mind the Empidomax complexity can be solved the easiest way I think is by song.
Also there is a Petersons advanced Birding paperback guide that goes into detail about the subtle differences on the Empid Flycatchers call notes, beak and mouth color, eye rings, and many more.
This Empid however I had conformation on his Fitz-Bew that it is a Willow Flycatcher , another interesting vocalization was subtle Pip notes he was uttering.