hawk owl vs bird of night

hawk owl and bird of night both are nouns.

Word	Noun	Adjective	Verb	Adverb
hawk owl	Yes	No	No	No
bird of night	Yes	No	No	No

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

hawk owl: grey-and-white diurnal hawk-like owl of northern parts of the Northern Hemisphere
bird of night: nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes

Other hypernyms of hawk owl include bird of Minerva, hooter, owl.

hawk owl (noun)	bird of night (noun)
grey-and-white diurnal hawk-like owl of northern parts of the Northern Hemisphere	nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes