Closely related to the Mouse-colored Antshrike (Thamnophilus murinus), from which males of the present species are distinguished reasonably easily by the lack of wing-spots, and the overall darker gray plumage, the Plain-winged Antshrike is a reasonably widespread inhabitant of lowland forest across, principally southern, Amazonia. In areas of overlap between them, principally in western Amazonia, females of the two species are often best distinguished by eye color, red in the present species, but gray or similarly dull in the Mouse-colored Antshrike. The two species’ songs are rather similar, at least to the observer less familiar with Amazonian birds. The present species’ loudsong over much of its range is a slightly accelerating series of even-pitched notes, terminating in an obvious downslur, but in parts of western Brazil and eastern Colombia (T. s. heterogynus) the song differs in being faster and lower-pitched. The Plain-winged Antshrike ranges from eastern Colombia south to northern Bolivia, and thence east across Amazonian Brazil virtually to the mouth of the river.