gaviiform seabird vs sea bird

gaviiform seabird and sea bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
gaviiform seabird	Yes	No	No	No
sea bird	Yes	No	No	No

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

gaviiform seabird: seabirds of the order Gaviiformes
sea bird: a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.

Other hypernyms of gaviiform seabird include seabird, seafowl.

gaviiform seabird (noun)	sea bird (noun)
seabirds of the order Gaviiformes	a bird that frequents coastal waters and the open ocean: gulls, pelicans, gannets, cormorants, albatrosses, petrels, etc.