Thick-billed fox sparrow
| Thick-billed fox sparrow | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Passeriformes |
| Family: | Emberizidae |
| Genus: | Passerella |
| Species: | P. (iliaca) megarhyncha |
| Trinomial name | |
| Passerella iliaca megarhyncha group Baird, 1858 |
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| Subspecies | |
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5-6, see article text |
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| Breeding ranges of the four fox sparrow groups | |
5-6, see article text
The thick-billed fox sparrow (Passerella (iliaca) megarhyncha) group comprises the peculiarly large-billed Sierra Nevadan taxa in the genus Passerella. It is currently classified as a "subspecies group" within the fox sparrow, pending wider-spread acceptance of its species status.
These birds were long considered members of the slate-colored fox sparrow group due to morphological characteristics (Swarth 1920), but according to mtDNA sequence and haplotype data (Zink 1994), it forms a recognizable clade. Research on suspected (Rising & Beadle 1996) hybridization and considering additional DNA sequence data led to confirmation of their distinctiveness (Zink & Kessen 1999); this group appears to be most closely related to the sooty and/or slate-colored fox sparrows. (Zink 1996, Zink & Weckstein 2003)
Thick-billed fox sparrows are almost identical in plumage to slate-colored fox sparrows but have a more extensive blue-gray hood and a less rusty tail. The most striking feature of this bird is its enormous beak which can appear to be three times as large as that of the markedly small-billed slate-colored fox sparrows. A thick-billed fox sparrow's beak also differs in color from that of the slate-colored. Although the culmens of both groups are grayish brown, slate-coloreds have yellow lower mandibles instead of the steel blue of the thick-billeds'. (Rising & Beadle 1996)
The megarhyncha complex breeds in mountains from southern Oregon to southern California east to the Sierra Nevada and shows little geographic variation. It interbreeds with the slate-colored complex along a narrow contact zone from southern Oregon to western Nevada (Rising & Beadle 1996) but as noted above, gene flow is quite limited. Sibley (2000) indicates that this group has the most diagnostic call note, "a high, flat squeak [sic] teep like California towhee".
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