The slate-colored fox sparrow (Passerella (iliaca) schistacea) group comprises the Rocky Mountain taxa in the genus Passerella. It is currently classified as a "subspecies group" within the fox sparrows pending a more-thorough genetic assay of all forms. It has long been suspected to be a separate evolutionary lineage due to morphological distinctness (Swarth 1920). More recently, it has been split into the present clade and the thick-billed fox sparrow. These have quite similar plumage, but can be readily distinguished according to mtDNA sequence and haplotype data (Zink 1994). However, these results were considered tentative (Rising & Beadle 1996) until more molecular data and apparent lack of wide-ranging hybridization coupled with ecological differences and adaptations led to confirmation of their distinctiveness (Zink & Kessen 1999); this group appears to be most closely related to the red fox sparrows (Zink & Weckstein 2003 contra Zink 1996), judging from biogeography. It breeds in relatively short willow habitats in montane regions from the interior of northwest British Columbia to Nevada and eastern California (Rising & Beadle 1996). It is a tiny-billed bird with a gray head and mantle, brown wings, brown breast streaks, and a russet tail.

Subspecies

Like all "fox sparrow" subspecies, it is differentiated into some morphologically recognizable allopatric populations, which are still genetically indistinguishable due to their recent evolution (Zink 1994). However, the handful or so of subspecies in this complex are poorly differentiated even morphologically for the most part; a two-subspecies arrangement recognizing the rather distinctive altivagans (the northern form) as distinct from the southern populations (schistacea) might be more reasonable (Rising & Beadle 1996). As with red and sooty fox sparrows, slate-coloreds also prefer to build their nests on the edges of wet habitat but are much less picky about in which plant they build. Their call note is a sharp klink according to Rising & Beadle (1996), or "a sharp smack, like Sooty and Red populations" according to Sibley (2000).