The Black-chinned Sparrow is an inconspicuous but locally common songbird of arid brushlands throughout the southwestern United States and south-central Mexico. In summer it favors rocky slopes of mixed chaparral or sagebrush from near sea level to almost 2,500 m. A partial migrant, in winter it generally moves downslope or south into desert scrub and dry wash. The retiring habits and remote haunts of this species render it one of the least-known songbirds of its region; little is known of its behavior, food, enemies, and most aspects of its breeding biology. Thus, this life history draws heavily from the anecdotal accounts and collected specimens of early-twentieth-century ornithologists.
In this species, the most strongly sexually dimorphic Spizella, the male's black chin patch, throat, and lores highlight a gray torso saddled with reddish brown back and wings. Always unassuming, both sexes are best located by voice: the male by its distinctive song, a pure-toned, accelerating trill nearly always delivered from a prominent perch; the female by its strident chipping near nest or young. Individuals seldom stray far from the protective cover of shrubbery, foraging in low brush for seeds and insects and flying through alleyways or low over bushtops.
Although regular and abundant on chaparral slopes fringing the Los Angeles Basin, where it is sometimes the most common species, its occurrence elsewhere can be irregular and unpredictable. Concurrent with documented declines in southern California is a possible post-1950 range extension north from central California to southern Oregon.
Four subspecies, based on variation in size and plumage coloration, are currently recognized. Subspecies character divergence is likely a response to differences in climate and migratory behavior across the range of this species.