Surnia ulula vs bird of night

Surnia ulula and bird of night both are nouns.

Word	Noun	Adjective	Verb	Adverb
Surnia ulula	Yes	No	No	No
bird of night	Yes	No	No	No

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

Surnia ulula: 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 Surnia ulula include bird of Minerva, hooter, owl.

Surnia ulula (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