Laura Erickson's For the Birds

This and the Cordilleran 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, the Cordilleran 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.

One subspecies of the Pacific-slope Flycatcher, found in the Channel Islands, may actually be a distinct species. It is larger than mainland populations, has a longer bill, a paler chest, slightly different vocalizations, and differs genetically.

I’m hoping the Cordilleran and Pacific-slope Flycatchers 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. Had I ever seen a Pacific-slope Flycatcher on Santa Cruz Island, lumping the larger populations wouldn’t help if they made the island population its own species, but I don’t think I saw any during my two visits to the Island in 2005 or 2013.