Original description: Embernagra brunnei-nucha La Fresnaye 1839
Taxonomic history in AOU/AOS Check-list
AOU 6 (1983): Chestnut-capped Brush-Finch, Atlapetes brunneinucha
AOU 7 (1998): Chestnut-capped Brush-Finch, Buarremon brunneinuchus
IUCN Conservation Status: Of least concern
Behavior: The handsome Chestnut-capped Brush Finch is skulky and shy, seldom leaving the dark, heavily vegetated forest thickets of foothills and mountains, where it quietly shuffles in search of seeds and small invertebrates; this species is said not to scratch with its feet while foraging, preferring instead to turn over leaves with its bill.
As might be deduced from its habitat choices and very short, rounded wing, this sparrow spends very little time in the air, and is virtually never seen in truly sustained flight. If it is flushed from its feeding place on the forest floor, it flutters away on shallow, whirring wing beats—or, more usually, scampers beneath the vegetation and out of sight.
Voice: The calls of the Chestnut-capped Brush Finch are surprisingly high, weak, and insect-like for a bird of its bulk. Single thin peek and seep notes sometimes run into a rapid excited series, especially when birds are agitated.
The rather variable song is no more impressive to human ears. Like the calls, the notes of the song are fine and high-pitched, most with a pronounced fingernails-on-the-chalkboard screeching tone, others with the hint of a liquid squeal behind them. Some songs comprise only a strictly rhythmic sequence of notes, spee spee spee-ur-seep; others incorporate soft popping sputters too irregular to be called a tremolo or trill.
Detailed description and measurements drawn from standard reference works
Adult Arremon brunneinucha brunneinucha: Tail feathers brownish green to olive. Upper tail coverts, rump, and back unstreaked olive-green. Primaries, secondaries, and tertials brownish green to olive. Greater and median coverts brownish green to olive; marginal coverts of underwing yellowish. Nape unstreaked olive-green.
Under tail coverts and vent light olive-greenish. Center of belly and breast whitish or grayish. Flanks olive-gray to olive-green; sides of breast gray. Narrow black band separating breast from bright white throat; jaw stripe white, no lateral throat stripe.
Crown chestnut or rusty. Ear coverts and lores black. Forehead black with small white median spot or stripe and two small lateral spots or stripes. Supercilium, and often extreme edge of crown, yellowish to orange-tan.
Tarsus and toes dark brown. Rather thick-based bill with curved culmen black.
Juvenile Arremon brunneinucha brunneinucha: Tail feathers brownish to olive-brown. Upper tail coverts, rump, and back olive-green with brown tinge. Primaries, secondaries, and tertials brownish green. Greater and median coverts brownish green. Nape olive-green.
Under parts dark brown. Belly and breast irregularly streaked pale yellowish, throat streaked and mottled yellowish-white.
Crown dark brown, paler and slightly rustier at edges. Ear coverts and lores dusky brown or blackish. Forehead blackish. Vague supercilium slightly yellowish.
Tarsus and toes dark brown. Rather thick-based bill yellowish with tip and curved culmen blackish.
Length 181-190 mm (7.1-7.5 inches)
Wing chord 82-86 mm (3.2-3.4 inches)
Tail 84-90 mm (3.3-3.5 inches)