auk vs sea bird

auk and sea bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
auk	Yes	No	No	No
sea bird	Yes	No	No	No

As nouns, sea bird is a hypernym of auk; that is, sea bird is a word with a broader meaning than auk:

auk: black-and-white short-necked web-footed diving bird of northern seas
sea bird: a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.

Other hypernyms of auk include seabird, seafowl.

auk (noun)	sea bird (noun)
black-and-white short-necked web-footed diving bird of northern seas	a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.