More specific information regarding plumage is available in the accounts for the various taxa.
P. i. iliaca – red fox sparrow (Merrem, 1786), is the generally central and east coast taxa in the genus Passerella. This is the brightest colored group.
P. i. unalaschcensis – sooty fox sparrow (Gmelin, JF, 1789), is the west coast taxa in the genus Passerella. It is browner and darker than the red fox sparrow.
P. i. schistacea – slate-colored fox sparrow Baird, SF, 1858, is the Rocky Mountain taxa in the genus Passerella. It is a tiny-billed bird with a gray head and mantle, brown wings, brown breast streaks, and a russet tail.
P. i. megarhyncha – thick-billed fox sparrow Baird, SF, 1858, is the Sierra Nevada taxa in the genus Passerella. This group features a particularly thick bill, as its name would suggest.
Adults are amongst the largest sparrows, heavily spotted and streaked underneath. All feature a messy central breast spot though it is less noticeable on the thick billed and slate-colored varieties. Plumage varies markedly from one group to another.
These birds forage by scratching the ground, which makes them vulnerable to cats and other predators, though they are generally plentiful. Fox sparrows migrate on the west coast of the United States.
They mainly eat seeds and insects, as well as some berries. Coastal fox sparrows may also eat crustaceans.
Fox sparrows nest in wooded areas across northern Canada and the west coast of North America from Alaska to California. They nest either in a sheltered location on the ground or low in trees or shrubs. A nest typically contains two to five pale green to greenish white eggs speckled with reddish brown.
The review of Zink & Weckstein (2003) which added mtDNAcytochrome b, NADH dehydrogenasesubunit 2 and 3, and D-loopsequence confirmed the four "subspecies groups" of the fox sparrow that were outlined by the initial limited mtDNA haplotype comparison (Zink 1994). These should probably be recognized as separate species, but this was deferred for further analysis of hybridization. Particularly the contact zones between the slate-colored and thick-billed fox sparrows which are only weakly distinct morphologically were of interest; the other groups were found to be distinct far earlier.
The combined molecular data is unable to resolve the interrelationship of the subspecies group and of subspecies in these, but aids in confirming the distinctness of the thick-billed group.Biogeography indicates that the coastal populations were probably isolated during an epoch of glaciation of the Rocky Mountains range, but this is also not very helpful in resolving the remaining problems of within-group diversity, and inter-group relationships.
^Ehrlich, Paul R.; Dobkin, David S.; Wheye, Darryl (1988). The Birder's Handbook: A Field Guide to the Natural History of North American Birds. New York: Simon and Schuster, Fireside. p. 596. ISBN0-671-65989-8.
^Zink, Robert M. (1994). "The Geography of Mitochondrial DNA Variation, Population Structure, hybridization, and Species Limits in the Fox Sparrow (Passerella iliaca)". Evolution48 (1): 96–111. doi:10.2307/2410006.
Weckstein, J. D., D. E. Kroodsma, and R. C. Faucett. (2002). Fox Sparrow (Passerella iliaca). The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Laboratory of Ornithology; Retrieved from The Birds of North American Online database
Blacquiere JR. M.Sc. (1980). Some aspects of the breeding biology and vocalizations of the fox sparrow, Passerella iliaca, Merrem, in Newfoundland. Memorial University of Newfoundland (Canada), Canada.
Kessen AE. Ph.D. (2004). Population structure in the fox sparrow: An investigation using microsatellites. University of Minnesota, United States—Minnesota.
Martin DJ. Ph.D. (1976). STRUCTURE OF SONGS AND ORGANIZATION OF SINGING IN FOX SPARROWS BREEDING IN NORTHERN UTAH AND SOUTHERN IDAHO. Utah State University, United States—Utah.
Zink RM. Ph.D. (1983). PATTERNS AND EVOLUTIONARY SIGNIFICANCE OF GEOGRAPHIC VARIATION IN THE SCHISTACEA GROUP OF THE FOX SPARROW (PASSERELLA ILIACA) (OREGON, NEVADA, CALIFORNIA). University of California, Berkeley, United States—California.
Anon. (1968). Fox Sparrow Very Rare Summer Resident 10-11-65 Swamp Sparrow Rare Winter Visitor 9-11-67 10-29-67 Lykins Gulch Colorado USA. Colorado Field Ornithologist. vol 4, pp. 13–14.
Banks RC. (1970). The Fox Sparrow on the West Slope of the Oregon Cascades. Condor. vol 72, no 3. pp. 369–370.
Bell CP. (1997). Leap-frog migration in the fox sparrow:: Minimizing the cost of spring migration. Condor. vol 99, no 2. pp. 470–477.
Blankson ENT & McKernan RL. (1995). Evolutionary and ecological considerations of seven subspecies of the fox sparrow (Passerella iliaca) wintering in California. Strauss, M. vol S, p. Unity in Diversity.
Burns KJ. (1993). Geographic variation in ontogeny of the fox sparrow. Condor. vol 95, no 3. pp. 652–661.
Burns KJ & Hackett SJ. (1993). Nest and nest-site characteristics of a western population of fox sparrow (Passerella iliaca). Southwestern Naturalist. vol 38, no 3. pp. 277–279.
Burns KJ & Zink RM. (1990). Temporal and Geographic Homogeneity of Gene Frequencies in the Fox Sparrow Passerella-Iliaca. Auk. vol 107, no 2. pp. 421–425.
Christie DS. (1968). Summer Occurrence of the Fox Sparrow in New-Brunswick Canada Passerella-Iliaca. Canadian Field Naturalist. vol 82, no 1.
Hubert P & Smith A. (1974). Possible Fox Sparrow Nesting in Minnesota. Loon. vol 46, no 1.
Jewer OD & Threlfall W. (1978). Parasites of the Fox Sparrow Passerella-Iliaca and Northern Waterthrush Seiurus-Noveboracensis in Newfoundland Canada. Proceedings of the Helminthological Society of Washington. vol 45, no 2. pp. 270–272.
Johnson JW & Johnson L. (1972). Fox Sparrow Observations in the Huron Area. South Dakota Bird Notes. vol 24, no 4.
Martin DJ. (1977). Songs of the Fox Sparrow Part 1 Structure of Song and Its Comparison with Song in Other Emberizidae. Condor. vol 79, no 2. pp. 209–221.
Martin DJ. (1979). Songs of the Fox Sparrow Passerella-Iliaca 2. Intra Population and Inter Population Variation. Condor. vol 81, no 2. pp. 173–184.
Martin DJ. (1980). Response by Male Fox Sparrows Passerella-Iliaca to Broadcast of Particular Con Specific Songs. Wilson Bulletin. vol 92, no 1. pp. 21–32.
Martin DJ. (1990). Songs of the Fox Sparrow 3. Ordering of song. Wilson Bulletin. vol 102, no 4. pp. 655–671.
Martin DJ, Naugler CT & Smith PC. (1993). Song similarity in populations of fox sparrows: A rejection of Naugler's and Smith's conclusions—Comment/reply. The Condor. vol 95, no 4. p. 1057.
Naugler CT & Smith PC. (1991). Song Similarity in an Isolated Population of Fox Sparrows Passerella-Iliaca. Condor. vol 93, no 4. pp. 1001–1003.
Peyton LJ. (1971). Geographical Variation of Fox Sparrow Songs in Alaska. Proceedings of the Alaska Science Conference. vol 22, no 39.
Robert MZ & Jason DW. (2003). Recent evolutionary history of the Fox Sparrows (Genus: Passerella). The Auk. vol 120, no 2. p. 522.
Ryan AG. (1974). An Incubation Period and a Nestling Period for the Fox Sparrow. Canadian Field Naturalist. vol 88, no 2. pp. 230–231.
Schmid U. (1979). 2 Rare Guest Birds on North Sea Island of Scharhoern West Germany Fox Sparrow Passerella-Iliaca and Scarlet Grosbeak Carpodacus-Erythrinus. Vogelkundliche Berichte aus Niedersachsen. vol 11, no 2. pp. 45–46.
Threlfall W & Blacquiere JR. (1982). Breeding Biology of the Fox Sparrow Passerella-Iliaca in Newfoundland Canada. Journal of Field Ornithology. vol 53, no 3. pp. 235–239.
Webster JD. (1975). The Fox Sparrow in Southwestern Yukon and Adjacent Areas. Condor. vol 77, no 2. pp. 215–216.
Webster JD. (1983). Passerella-Iliaca-Chilcatensis New-Subspecies a Fox Sparrow from Alaska USA. Proceedings of the Biological Society of Washington. vol 96, no 4. pp. 664–668.
Zink RM. (1983). Evolutionary and Systematic Significance of Temporal Variation in the Fox Sparrow Passerella-Iliaca. Systematic Zoology. vol 32, no 3. pp. 223–238.