Original description: Passerella megarhynchus Baird 1858
Taxonomic history in AOU/AOS Check-list
AOU 1 (1886): Thick-billed Sparrow, Passerella iliaca megarhyncha
AOU 2 (1895): Thick-billed Sparrow, Passerella iliaca megarhyncha
AOU 3 (1910): Thick-billed Fox Sparrow, Passerella iliaca megarhyncha; Stephens’s Fox Sparrow, Passerella iliaca stephensi
AOU 4 (1931): Warner Mountain Fox Sparrow, Passerella iliaca fulva; Thick-billed Fox Sparrow, Passerella iliaca megarhyncha; Trinity Fox Sparrow, Passerella iliaca brevicauda; Mono Fox Sparrow, Passerella iliaca monoensis; Yosemite Fox Sparrow, Passerella iliaca mariposae; Stephens’s Fox Sparrow, Passerella iliaca stephensi
AOU 5 (1957): Fox Sparrow, Passerella iliaca fulva, Passerella iliaca megarhyncha, Passerella iliaca brevicauda, Passerella iliaca monoensis, Passerella iliaca stephensi
AOU 6 (1983): Fox Sparrow, Passerella iliaca
AOU 7 (1998): Fox Sparrow, Passerella iliaca [megarhyncha group, Thick-billed Fox-Sparrow]
IUCN Conservation Status: Of least concern
The habitats used by the Thick-billed Fox Sparrow are not believed to have been affected recently by human activity.
Habitat: Breeding birds occur in damp deciduous thickets between 3,000 and 10,000 feet in elevation; in winter, they occupy chaparral and riparian habitats, especially on south-facing slopes.
Behavior: Like the other fox sparrows, the Thick-billed is a shy but noisy ground feeder, hopping and scratching through leaf litter beneath or very near dense vegetation.
Thick-billed Fox Sparrows are rarely seen in anything approaching sustained flight, instead fluttering into brush with the long tail a-twitch. The flight call—often given by alert perched birds as well—is nearly identical to those of the other fox sparrows, but is lower pitched and less decidedly slurred than the corresponding calls of the Sooty and Red Fox Sparrows; it is practically indistinguishable from that of the Slate-colored. As in other fox sparrows, both sexes are known to sing.
Voice: Unlike the low-pitched, smacking contact notes of the other fox sparrows, this species has a light, bright tdink, higher-pitched and more musical, closer in tone to a California Towhee’s or, especially, a White-crowned Sparrow’s chip. An alarmed fox sparrow of any species may also give a series of high-pitched tsip notes, “spectrographically distinct from the ‘tink’ calls of Thick-billed Fox Sparrows, but [which] can be quite difficult to distinguish by ear.” Waiting, if possible, for the agitation to subside offers the best chance that a bird will return to issuing its typical and distinctive contact note.
The song of the Thick-billed Fox Sparrow in Nevada was praised by Robert Ridgway “as second to none… though in variety, sprightliness, and continuity, and also in passionate emotional character, its song is not equal to that of the [Lark Sparrow], yet it is far superior in power and richness of tone.”
A loud, melodic series of phrases, it resembles the songs of the Sooty and Slate-colored Fox Sparrows in the insertion of rich buzzy notes within and between phrases; some Thick-billed appear to sing a slightly longer song than most Slate-colored Fox Sparrows, but it is not known whether this difference is consistent at the level of populations and thus useful for field identification.
Detailed description and measurements drawn from standard reference works
Adult Passerella megarhyncha megarhyncha: Tail feathers and upper tail coverts bright brown. Rump, back, scapulars, and nape unstreaked medium gray. Primaries brown with paler brown edges; secondaries and tertials rusty brown with paler edges. Greater and median coverts rusty brown with dull whitish tips very indistinct or entirely absent.
Under tail coverts gray brown with conspicuous pale buffy tips and edges. Vent, belly, breast, and throat white with black spots and chevrons, heaviest on upper breast, where they form an extensive ill-defined smudge. Flanks with discrete black spots and streaks. Throat white with heavy blackish flecking; separated from speckled white jaw stripe by short, poorly defined lateral throat stripe. Ear coverts medium gray, faintly streaked whitish and faintly outlined by blackish whisker below and blackish eye line above.
Crown medium gray. Very fine white eye ring, broken behind by faint blackish eye line. Lore and irregularly shaped spot above lore gray with variable whitish speckling.
Tarsus and toes dull pink. Large to very large, thick-based, broad bill light gray to yellow below and on edges of upper mandible; remainder of upper mandible dark gray.
Juvenile Passerella megarhyncha megarhyncha: Gray upperparts more noticeably brown-tinged. Greater and median coverts with indistinct pale rusty tips.
Underparts dull white, dark markings less black and less clearly wedge-shaped.
Length 165-183 mm (6.5-7.2 inches)
Wing chord 75-87 mm (3.0-3.4 inches)
Tail 77-87 mm (3.0-3.4 inches)
Mass 33 g