In Arizona, the “Western Flycatcher” complex historically referred to two nearly identical species, the Cordilleran Flycatcher (Empidonax occidentalis) and the Pacific-slope Flycatcher (Empidonax difficilis). These two Empidonax flycatchers are notoriously difficult to distinguish by sight alone, as both have olive-green upperparts, yellowish underparts, eye-rings, and wingbars. In fact, until the early 1980s, they were considered a single species under the name Western Flycatcher.
Both species occur in Arizona, though most breeding records in the state are attributed to the Cordilleran Flycatcher (Empidonax occidentalis). This species is typically found in montane forests of pine, fir, and mixed conifers in the “sky islands” of southeastern Arizona, including the Chiricahuas, Huachucas, and Santa Catalinas. They arrive in late spring, nest in shaded areas often near water, and depart by fall migration.
The Pacific-slope Flycatcher (Empidonax difficilis) is more coastal in distribution but does occur as a migrant in Arizona, primarily in the lower desert regions during spring and fall. Because of the nearly indistinguishable plumage, many Arizona reports of “Western Flycatcher” are left identified only to the complex unless vocalizations or genetic analysis are available. Songs and calls are one of the most reliable field distinctions: Empidonax occidentalis has a sharper, higher-pitched “pit-seet” call compared to the softer “psseet” of Empidonax difficilis.
Overall, the Western Flycatcher group in Arizona exemplifies the challenges of identifying Empidonax flycatchers. While Empidonax occidentalis is a breeding bird of Arizona’s mountains, both species (or at least individuals from the complex) pass through the state during migration, and most birders record them cautiously as “Western Flycatcher (Empidonax difficilis/occidentalis).”
