The Slate-colored Fox Sparrows (Passerella (iliac) schistacea) group is 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 and Beadle 1996) until more molecular data and an apparent lack of wide-ranging hybridization coupled with ecological differences and adaptations led to confirmation of their distinctiveness (Zink and Kessen 1999); this group appears to be most closely related to the Red Fox Sparrows (Zink and 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 and Beadle 1996).
The Slate-colored Fox Sparrows is a tiny-billed bird with a gray head and mantle, brown wings, brown breast streaks, and a russet tail.
Sub-species, Range and Identification:
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 (Zink 1994).
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 and Beadle 1996).
As with Red and Sooty Fox Sparrows, Slate-coloreds also prefer to build their nests on the edges of wet habitats but are much less picky about in which plant they build. Their call note is a sharp klink according to Rising and Beadle (1996), or “a sharp smack, like Sooty and Red populations” according to Sibley (2000).
- schistacea Baird, 1858:
Breeds from Crowsnest Pass (British Columbia) and Waterton Lakes Park (SW Alberta) south through the Great Basin mountain ranges. Patchily distributed towards 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 Southern 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 and Beadle 1996).
- altivagans Riley, 1911:
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 the back is noticeably brown, and the wings and tail with pronounced rusty wash. Altogether, it intermediate between schistacea and the Eastern Fox Sparrow (P. (iliaca) iliaca) in morphology, but is well distinguished from the latter by vocal and molecular characteristics (Rising and 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).
- canescens Swarth, 1918:
Breeds in mountain ranges in C Nevada, notably the Shoshone Mountains, 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 and Beadle 1996).
- olivacea Aldrich, 1943:
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 and Beadle 1996). Intermediate between this form and the full 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 and 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 a heavy breast pattern, but as it intergrades with schistacea and canescens (Weckstein et al. 2002) doubtfully distinct from the former (Rising and Beadle 1996).
Breeding / Nesting:
As with Reds and Sooties, Slate-coloreds also prefer to build their nests on the edges of wet habitats but are much less picky about in which plant they build.
Call / Song:
Their call note is a sharp klink according to Rising (1996), or “a sharp smack, like Sooty and Red populations” according to Sibley (2000).