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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"〔Not defined by the ICZN〕 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 cytochrome ''b'' 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.〔 Etymology: ''megarhyncha'', "large-billed", from Ancient Greek ''mega''-, "great" + ''rhynchos'', "beak".〕 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) ==Subspecies== 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 ''teep'' like California towhee". * ''megarhyncha'' Baird, 1858: :Breeds from Onion Mountains and Robinson's Butte (southwest Oregon) south through inland northern California to Kearsarge Pass (Inyo County), as well as the western flank of the Sierra Nevada in Mono County. Winters in central and southern California and adjacent Mexico.(Weckstein ''et al.'' 2002) :More large-billed, duller, and grayer than ''schistacea'' slate-colored fox sparrows; intermediate between the very large long-tailed ''stephensi'' and the more ''schistacea''-like ''monoensis'' of this group; intergrades with former.(Weckstein ''et al.'' 2002) * ''stephensi'' Anthony, 1895: :Breeds in areas of the southern Sierra Nevada such as Fresno and Tulare Counties, Mount Pinos and San Gabriel, San Bernardino, and San Jacinto Mountains, California, to the Sierra San Mártir, northern Baja California. In winter, migrates to lower elevations but generally does not migrate long distances. (Weckstein ''et al.'' 2002) :The largest, most massive-billed and longest-tailed fox sparrow; also very gray in coloration. (Swarth 1920) Intergrades with ''megarhyncha''. (Weckstein ''et al.'' 2002) * ''monoensis'' Grinnell & Storer, 1917: :Breeds on the eastern flank of the Sierra Nevada in Mono County, California, and in the Walker River Range in adjacent Mineral County, Nevada. Winters from inland central California coastwards and south into Mexico. (Weckstein ''et al.'' 2002) :Somewhat intermediate between ''megarhyncha'' and ''schistacea'' slate-colored fox sparrows, with a paler, ashy gray back. (Weckstein ''et al.'' 2002) * ''brevicauda'' Mailliard, 1918: :Breeds in the Mendocino Range of California, from the Yolla Bolly Mountains south to Snow Mountain and Sanhedrin Mountains. Migrates coastwards and south in winter. (Weckstein ''et al.'' 2002) :Similar to ''stephensi'', but recognizable by more rusty tinge to brownish areas and the conspicuously shorter tail. (Weckstein ''et al.'' 2002) * ''fulva'' Swarth, 1918: :Mountaineous regions from central Oregon east of Cascades Range (Steens Mountain, Sisters and Keeno Mountains) to Modoc and Lassen Counties, California. Winters in southwesternmost California and adjacent Mexico. :A browner version of ''monoensis''; in winter range, distinguished from ''olivacea'' slate-colored fox sparrows by decidedly ruddy brown and larger bill. (Weckstein ''et al.'' 2002) * ''mariposae'' Swarth, 1918: :Breeding in a limited area in California between the headwaters of the Little Shasta River (Siskiyou County) to Yosemite National Park and Kearsarge Pass. Winter range undocumented (Weckstein ''et al.'' 2002) due to lack of distinctiveness but probably same as ''megarhyncha'' and ''monoensis''. :Probably nothing more than intergrades between ''megarhyncha'' and ''monoensis''; nowadays usually synonymized with the former. (Rising & Beadle 1996) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Thick-billed fox sparrow」の詳細全文を読む スポンサード リンク
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