Medium-sized blackbird with a long, thin bill that is found in marshes and reedbeds. Males are all black, whereas females are highly variable across their range. Northern females from Amapá, Pará, Maranhão, and French Guiana are mostly black with an olive belly. Those from southeast Brazil are dark brownish olive above and dark yellow below. Those from central-southern South America are brown above with black streaks, a faint yellow eyebrow, and yellow underparts. The song is a rattle followed by a series of trills.