The White-headed Marsh Tyrant (Arundinicola leucocephala) is a small passerine bird in the tyrant flycatcher family, the only species of the genus Arundinicola. It breeds in tropical South America from Colombia, Venezuela and Trinidad south to Bolivia, Argentina and Paraguay. The adult White-headed Marsh Tyrant is 12.7 cm long and weighs 15 g. The male is entirely brown-black, apart from the relatively large white head and yellowish lower mandible. The female has brown upperparts and wings and a black tail. Her underparts, sides of the head and forecrown are dull white. This is a quiet species, but the call is a sharp sedik.