tawny owl vs bird of night

tawny owl and bird of night both are nouns.

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

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

tawny owl: reddish-brown European owl having a round head with black eyes
bird of night: nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes

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

tawny owl (noun)	bird of night (noun)
reddish-brown European owl having a round head with black eyes	nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes