hoatzin vs gallinaceous bird

hoatzin and gallinaceous bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
hoatzin	Yes	No	No	No
gallinaceous bird	Yes	No	No	No

As nouns, gallinaceous bird is a hypernym of hoatzin; that is, gallinaceous bird is a word with a broader meaning than hoatzin:

hoatzin: crested ill-smelling South American bird whose young have claws on the first and second digits of the wings
gallinaceous bird: heavy-bodied largely ground-feeding domestic or game birds

Other hypernyms of hoatzin include gallinacean.

hoatzin (noun)	gallinaceous bird (noun)
crested ill-smelling South American bird whose young have claws on the first and second digits of the wings	heavy-bodied largely ground-feeding domestic or game birds