On the morning of 28 May 2016, Stejskal discovered an Empidonax flycatcher at Aliso Spring in the Santa Rita Mountains, Pima County, Arizona (31° 44’ 08” N, 110° 48’10” W). First hearing a distinctive “whit” note of an Empidonax, thinking it was likely from either a Dusky Flycatcher (E. oberholseri) or a Gray Flycatcher (E. wrightii), and realizing that either species would be unusual in southeastern Arizona in late May, he decided to locate and document the bird. Upon finding the flycatcher, he noticed that it appeared odd, appearing superficially like a Dusky but having an entirely orange lower mandible, as in a Western Flycatcher (E. occidentalis or E. difficilis). The bird also appeared to be investigating potential nesting sites, which would be unprecedented for either the Dusky Flycatcher or the Gray Flycatcher in this region of Arizona. That morning and afternoon, and the following morning, he photographed the bird extensively and recorded its call notes. Upon his return to Tucson on 29 May he sent both the photos and sound recordings to Chris D. Benesh and to Rosenberg for opinion and analysis. He suspected the bird was a Pine Flycatcher (E. affinis), with which he was familiar from the mountains of western Mexico. Benesh and Rosenberg compared the photos directly to photos published online of both the Dusky and Pine Flycatchers and, more importantly, compared sonograms of the call notes of the Aliso Spring bird directly to recordings of both the Dusky and Pine flycatchers that they had recorded and uploaded to www.xeno-canto.org