Isleria hauxwelli ( Sclater, 1857 )

Isler, Morton L., Chesser, R. Terry, Stryjewski, Katherine Faust & Whitney, Bret M., 2025, Systematics of three pan-Amazonian antwren lineages (Aves: Passeriformes: Thamnophilidae: Myrmotherula and Isleria), Zootaxa 5722 (1), pp. 45-78 : 69

Isleria hauxwelli ( Sclater, 1857)

Plain-throated Antwren

Includes the populations designated hauxwelli- W, hauxwelli- C, hauxwelli- E, and hellmayri in the analysis.

Diagnosis. Distinctions in note structure and frequency band width distinguish Songs of I. hauxwelli from those of I. guttata ( Fig. 11), and Alarm Calls differ in the number of elements and duration ( Fig. 12). Male differs from I. guttata in having gray rather than tawny posterior underparts and smaller white (rather than pale cinnamon) wing and tail spots.

Description of plumage. Male is gray, paler below, throat whitish; interscapular patch white (except I. h. hellmayri); wings and tail blackish brown, remiges edged white; wing covert tips and spots on tertials and tail white. Female like male except upperparts paler gray washed cinnamon-rufous; underparts tawny-cinnamon, throat paler, flanks tinged olive; remiges edged cinnamon.

Distribution. Bounded on the north in Brazil by the Rio Amazonas west along the south bank of the Rio Solimões to the mouth of the Rio Japurá, Brazil; thence north, south of the Rio Japurá, to the vicinity of Rio Guainía, Colombia; thence west to near the base of the Andes in Meta, Colombia; thence south along the base of the Andes to La Paz, Bolivia; and thence east, north of Amazonian forest limits from Pando, Bolivia, to eastern Pará and western Maranhão, Brazil.

Remarks. Within I. hauxwelli , a vocal distinction in the Song of study population hauxwelli- W and the absence of an interscapular patch in study population hellmayri support three subspecies within I. hauxwelli : I. h. hauxwelli in the west, I. h. hellmayri in the east; and I. h. clarior (as below) in the center of the range. In an apparent clinal pattern, males become darker in plumage from east to west (except paler in northeastern Bolivia), with no diagnostic differences in coloration between adjoining populations. Female coloration provides less of a clinal pattern than males as I. h. hellmayri females are dark in contrast to the pale males of that subspecies.