|Empidonax occidentalis||Order: Passeriformes||Family: Tyrannidae (Tyrant Flycatchers)|
This and the Pacific-slope Flycatcher were once considered a single species, the Western Flycatcher, and some taxonomists believe they really are just two subspecies of the same species so they may be re-lumped. The two species are essentially identical as far as measurements and plumage go, but the calls of male Pacific-slope Flycatchers have a single syllable while those of Cordillerans have two syllables. During the breeding season, they are found in two different areas, this one sticking to the Rocky Mountains and Mexico’s Sierra Madre while the Pacific-slope Flycatcher is found west of there, in the forests and mountains along the West Coast. Their ranges do overlap in some parts of the Northwest, and there they hybridize. In this area, it’s hard to be sure if vocalizations were made by one or the other, or by hybrids. Both species winter in essentially the same area of Mexico, where it’s impossible to distinguish them since they only make their distinctive calls during the breeding season.
I’m hoping the two do get lumped. I’ll lose a species on my life list, but that will bump the Smooth-billed Ani, one of my favorite birds, into the #700 position on my ABA Continental List.