The Undulated Antshrike is a species of large antshrike in the monotypic genus Frederickena that is distributed throughout western Amazonia in northeastern Ecuador, southern Colombia, south through eastern Peru and western Brazil to northern Bolivia. Males are black with very fine grayish-white barring throughout. Females are entirely rusty-brown with black barring. Both sexes have a long bushy crest that it often hold flat. Two subspecies described, with birds south of the Amazon River differing mainly in the females, which are buffier, and less barred underneath. Found mainly in isolated pairs in the understory of terra firme forst, where birds stay mostly hidden in dense thickets. Song is a series of 10-15 clear whistles “wur-wee-wee-wee-wee-wee-wee…,” often on one pitch, but sometimes with notes rising in pitch and intensity. Unlike other species of Thamnophilids in Amazonia. Fasciated Antshrike (Cymbilaimus lineatus) is somewhat similar, and overlaps with Undulated, but has a black crown (less crested), a red iris, frequents vine tangles in the mid-story and sub-canopy, and has a very different song.