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 by 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
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