Strix varia vs bird of night

Strix varia and bird of night both are nouns.

Word	Noun	Adjective	Verb	Adverb
Strix varia	Yes	No	No	No
bird of night	Yes	No	No	No

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

Strix varia: large owl of eastern North America having its breast and abdomen streaked with brown
bird of night: nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes

Other hypernyms of Strix varia include bird of Minerva, hooter, owl.

Strix varia (noun)	bird of night (noun)
large owl of eastern North America having its breast and abdomen streaked with brown	nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes