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The many described subspecies of the Fox Sparrow (Passerella iliaca) have been parsed into four groups, the Red (iliaca group, two or three subspecies), Sooty (unalaschcensis group, seven subspecies), Thick-billed (megarhyncha group, five subspecies) and Slate-colored (schistacea group, four subspecies). Intermediate populations and contact areas between these groups play a role in answering the question whether any of the groups should be considered separate species. P. i. canescens of the Slate-colored group shows genetic characters of both the Slate-colored and Thick-billed groups. As currently classified it comprises two disjunct populations, one breeding in the White Mountains of California and Nevada, the other in the Toiyabe Range of central Nevada. We analyzed the vocalizations and bill sizes of these two populations to see if this might shed light on their taxonomic relationships. Our analyses of song, call, and bill measurements, along with a re-examination of previously published morphologic and genetic data, suggest that the two disjunct populations currently assigned to P. i. canescens represent different subspecies: the central Nevada population P. i. schistacea (in the Slate-colored group) and the White Mountains population P. i. megarhyncha (in the Thick-billed group), thus eliminating P. i. canescens as a synonym. Our findings may have implications for any future proposals to split the Fox Sparrow groups into distinct species. If that split results in the Slate-colored and Thick-billed groups assigned to separate species, our results would include the White Mountains population in the Thick-billed species and the central Nevada population in the Slate-colored species. [ABSTRACT FROM AUTHOR]