Myrmotherula omissa Todd, 1927

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 : 63

Myrmotherula omissa Todd, 1927 , subspecies elevated to species

Eastern Gray Antwren

Includes the study populations designated omissa- E and omissa- W in the analysis.

Diagnosis. Myrmotherula omissa is distinguished from M. cinereiventris and M. menetriesii s.s. by vocalizations and plumage. The structure of individual notes distinguishes Songs of Myrmotherula omissa from those of M. cinereiventris ( Fig. 6), and the sequence of abrupt notes and longer downslurred notes in Long Calls of Myrmotherula omissa differs from those in Long Calls of both M. cinereiventris and M. menetriesii ( Fig. 7). Males of omissa differ from M. menetriesii s.s. by the absence of black patches on throat and upper breast.

Description of female plumage. Female upperparts are Olive Gray (generally 5Y4/1 for omissa- E and 5Y4/2 for omissa –W, but with intermediates); underparts typically Brownish Yellow (10YR6/8) but sometimes as light as Yellow Ochre (10YR7/6) and therefore not entirely distinguishable from those of menetriesii s.s. or cinereiventris , but tend to be paler on chin and sides of head.

Distribution. Bounded on the north by the Amazon River, forest limits in central Isla Marajó, and the Atlantic Ocean; on the east by the Rio Pindaré, Maranhão; on the southeast by Amazonian forest limits; and on the southwest in the region between the lower Rio Madeira/lower Rio Aripuanã/lower Rio Roosevelt and the headwaters of the Rio Teles Pires.

Remarks. Some male specimens of M. omissa have a scattering of black spots on the throat and upper breast. Specific status for Myrmotherula omissa is reinforced by mtDNA genetic distances of ~5.9% among the three species that formerly constituted M. menetriesii . The intersection of the geographic ranges of M. omissa and M. menetriesii berlepschi is unclear and awaits further field exploration. The genetic analysis identified mtDNA genetic distances of 1.6% between study populations omissa -E and omissa- W, but no diagnostic vocal characters were found, although female plumage may differ.