The Slate-colored Fox Sparrow (Passerella (iliaca) schistacea} group are the Rocky Mountain taxa in the genus Passerella. It is currently classified as a "subspecies group
within the Fox Sparrow pending wider-spread acceptance of species status.
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 are morphologically quite similar, 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 is found to breed in mountaineous 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.
Like all "Fox Sparrow" subspecies
, it is differentiated into some morphologically recognizable allopatric
populations, which are still genetically indistinguishable however due to their recent evolution
However, the handful or so 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 sharp klink according to Rising & Beadle (1996), or "a sharp smack, like Sooty and Red populations" according to Sibley (2000).
- Breeds from Crowsnest Pass (British Columbia) and Waterton Lakes Park (SW Alberta) south through the Great Basin mountain ranges. Patchily distributed to wards the southern end of its range, it ranges as far as northern Nevada (Humboldt County, Elko County), Fort Bridger, Wyoming), and Cochetopa Creek (W Colorado). Moves coastwards in winter, occurring mainly in S California.(Weckstein et al. 2002)
- The nominate subspecies of the group, its head and back are slate grey, with a brown wash on the back. Wings, rump, tail, crown and underside spotting are a rich darkish brown, somewhat more rusty on the tail (Rising & Beadle 1996).
- Breeds inland from C British Columbia to the area of Crowsnest Pass. In winter, mainly in the Cascade Range and Sierra Nevada, California, and coastal areas to the southwest of this south to northernmost Mexico.(Weckstein et al. 2002)
- Overall similar to schistacea, but back noticeably brown and wings and tail with pronounced rusty wash. Altogether, intermediate between schistacea and the Eastern Fox Sparrow (P. (iliaca) iliaca) in morphology, but well distinguished from latter by vocal and molecular characters (Rising & Beadle 1996). Considerable variation in this population suggests some hybridization with the Sooty Fox Sparrow subspecies fuliginosa and the Yukon Fox Sparrow, as well as intergradation with schistacea (around Banff) and the doubtfully distinct olivacea (Weckstein et al. 2002).
- Breeds in mountain ranges in C Nevada, notably the the Shoshone Mountains, and the Toiyabe, and Monitor Ranges, and the White Mountains, California. Winters in the California-Arizona-Mexico border area.(Weckstein et al. 2002)
- Similar to schistacea sensu stricto and doubtfully distinct from it; somewhat greyer overall (Rising & Beadle 1996).
- Breeds from the Nelson area (British Columbia) south along the E slopes of the Cascade Range probably to N Idaho and NW Montana, reaching east as far as the Blue Mountains of Oregon. In winter, migrates to California (Tehama County, Piute Mountains) and the Sierra Juárez in N Mexico.(Weckstein et al. 2002)
- Doubtfully distinct from schistacea sensu stricto (Rising & Beadle 1996). Intermediate between this form and the fulva Thick-billed Fox Sparrows ; darker and browner than the first, and brown olive- rather than red-tinged; bill small as in schistacea with which it intergrades.(Weckstein et al. 2002)
- swarthi Behle & Selander, 1951:
- Breeds from Bannock County and Bear Lake County, Idaho, through mountain ranges in Utah south to Sanpete County. Winter range unknown.(Weckstein et al. 2002)
- A very grey form with heavy breast pattern, but as it apparently intergrades with schistacea and canescens (Weckstein et al. 2002) doubtfully distinct from the former (Rising & Beadle 1996).
- Rising, Jim D. & Beadle, David (1996): A Guide to the Identification and Natural History of the Sparrows of the United States and Canada. Academic Press, San Diego. ISBN 0-12-588971-2
- Sibley, David Allen (2000): The Sibley Guide to Birds. Alfred A. Knopf, New York. ISBN 0-679-45122-6
- Swarth H. W. (1920): Revision of the avian genus Passerella with special reference to the distribution and migration of the races in California. ''University of California Publications in Zoology 21: 75–224.
- Weckstein, J. D.; Kroodsma, D. E. & Faucett, R. C. (2002): Fox Sparrow (Passerella iliaca). In: Poole, A. & Gill, F. (eds.): The Birds of North America 715. Academy of Natural Sciences, Philadelphia, PA & American Ornithologists' Union, Washington, D.C. Online version, retrieved 2006-11-27. (requires subscription)
- Zink, R. M. (1994): The Geography of Mitochondrial DNA Variation, Population Structure, hybridization, and Species Limits in the Fox Sparrow (Passerella iliaca). Evolution 48(1): 96-111. (HTML abstract, first page image)
- Zink, Robert M. & Kessen, A. E. (1999): Species Limits in the Fox Sparrow. Birding 31: 508-517.
- Zink, Robert M. & Weckstein, Jason D. (2003): Recent evolutionary history of the Fox Sparrows (Genus: Passerella). Auk 120(2): 522–527. [Article in English with Spanish abstract] DOI: 10.1642/0004-8038(2003)120[0522:REHOTF]2.0.CO;2 HTML fulltext (without images)