Willow Flycatchers Empidonax traillii is one of a family of notoriously difficult to identify genus of flycatchers that birders refer to as "empids" that are most easily identified on their breeding grounds by their songs and calls. In the area I live we have resident Pacific-slope flycatchers Empidonax difficilis and Hammond's Flycatchers Empidonax hammondii that return by early to mid May of each spring from their wintering grounds, and then it seems like a long wait for our other common breeding "empid" the Willow Flycatcher.
This Willow Flycatcher was typical of the early returning birds, as it was perched in a brushy open forest edge singing from an open perch loudly and repeatedly. It's song is remembered by the mnemonic "Fitz-bew" which is not at all like our other resident or common migrant "empids", and could only be comfused with Alder Flycatcher Empidonax alnorum by voice, and Alder Flycatchers are extraordinarily rare here.
Willow Flycatchers are notable visually by having a very minimal eyering, and relatively faint wingbars, a clean white throat, a yellow lower mandible, and with wings that are considerably shorter than the somewhat similar Western Wood Pewee.
I think of Willow Flycatchers being a sign that summer is almost here, because they don't return until late May.
A Western Wood Pewee for comparison.
Welcome back Willow Flycatchers. Good birding.