The Giant Cowbird is a relatively quiet icterid (Skutch 1954, Skutch 1996, Jaramillo and Burke 1999).
Song: The song of the Giant Cowbird is short, and has a screeching quality. It has been described in various ways by different authors, e.g.: a "spluttering, ascending screech" given during courtship (Skutch 1954, 1996); "a somewhat strident, tri-syllabic whistle, tew-tew-hee, the last note much higher pitched" (ffrench 1980); "estrofe estridente mas melodiosa: tjüli, tchi, tchi, tchi, tchi (Sick 1985, 1993); "an unattractive, spluttering, ascending screech: fwrreeeeee? (Stiles and Skutch 1989); "a rather unpleasant, screechy whistle followed by 3 or more short notes with a metallic quality ... Tchwweeeee, twii-dlee, tic-tic or Shhweaa, t-pic-pic (Jaramillo and Burke 1999); "a remarkable variety of odd, disconnected notes incl[uding] an ascending, screeching freeeeeee; some notes sound electronic or mechanical (Hilty 2003); and "a series of high-pitched rusty screeches and creaks, like unoiled hinges" (Lane in Schulenberg et al. 2007) .
Females give "harsh, nasal whistles" when pursued by oropendolas in nest defense (Skutch 1954, Skutch 1996).
Other calls are a sharp, loud, grating series dzt-dzt-dzt (ffrench 1980) and a more musical pernt uttered in flight (ffrench 1980, Skutch 1954, 1996); sharp and chatty chechk chehk or chehk-chick, a longer chrrik rrik-rrik-rrik-rrik-rrik-rrik (Jaramillo and Burke 1999); a "mew"; and a low dak or kawk (Jaramillo and Burke 1999).
No geographic variation in the vocal repertoire has been described. There is little or no information on the daily or annual pattern of song, or on the social context and presumed functions of most vocalizations of the Giant Cowbird.