night raven vs night bird

night raven and night bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
night raven	Yes	No	No	No
night bird	Yes	No	No	No

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

night raven: any bird that cries at night
night bird: any bird associated with night: owl, nightingale, nighthawk, etc

night raven (noun)	night bird (noun)
any bird that cries at night	any bird associated with night: owl, nightingale, nighthawk, etc
nocturnal or crepuscular herons