night raven vs heron

night raven and heron both are nouns.

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

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

night raven: nocturnal or crepuscular herons
heron: grey or white wading bird with long neck and long legs and (usually) long bill

night raven (noun)	heron (noun)
any bird that cries at night	grey or white wading bird with long neck and long legs and (usually) long bill
nocturnal or crepuscular herons