Otus asio vs bird of night

Otus asio and bird of night both are nouns.

Word	Noun	Adjective	Verb	Adverb
Otus asio	Yes	No	No	No
bird of night	Yes	No	No	No

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

Otus asio: small North American owl having hornlike tufts of feathers whose call sounds like a quavering whistle
bird of night: nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes

Other hypernyms of Otus asio include bird of Minerva, hooter, owl.

Otus asio (noun)	bird of night (noun)
small North American owl having hornlike tufts of feathers whose call sounds like a quavering whistle	nocturnal bird of prey with hawk-like beak and claws and large head with front-facing eyes