mollymawk vs pelagic bird

mollymawk and pelagic bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
mollymawk	Yes	No	No	No
pelagic bird	Yes	No	No	No

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

mollymawk: large web-footed birds of the Southern Hemisphere having long narrow wings; noted for powerful gliding flight
pelagic bird: bird of the open seas

Other hypernyms of mollymawk include oceanic bird.

mollymawk (noun)	pelagic bird (noun)
large web-footed birds of the Southern Hemisphere having long narrow wings; noted for powerful gliding flight	bird of the open seas