The California Gnatcatcher (Polioptila californica) was first described as a new species by Brewster (1881) from specimens collected at Riverside, California. Later, Grinnell (1926) merged it with Polioptila melanura, as a subspecies.
Phillips (1980) and Rea (1983) considered it a different species, and Atwood (1988), in a taxonomic revision of the black-tailed gnatcatcher complex, demonstrated that the two forms are sympatric in Baja California on the east side of the central peninsula (29°–31° N), have distinctly different vocalizations, and mate non-randomly.