black-backed gull vs Larus marinus

black-backed gull and Larus marinus both are nouns.

Word	Noun	Adjective	Verb	Adverb
black-backed gull	Yes	No	No	No
Larus marinus	Yes	No	No	No

As nouns, black-backed gull and Larus marinus are synonyms defined as:

black-backed gull and Larus marinus: white gull having a black back and wings

Other synonyms of black-backed gull include cob, great black-backed gull.

black-backed gull (noun)	Larus marinus (noun)
white gull having a black back and wings	white gull having a black back and wings