The White-headed Marsh Tyrant perches on aquatic plants and reeds, and the sexes have different plumage. Records are also confirmed in Argentina.
The male has a black body with a conspicuously white head. The female has a white forehead, brown back and pale underparts.
The university account says it perches alone or in pairs on reeds and aquatic plants, then catches small flying prey in the air.
An extinction-risk assessment has not been added yet.