scoter vs common scoter

scoter and common scoter both are nouns.

Word	Noun	Adjective	Verb	Adverb
scoter	Yes	No	No	No
common scoter	Yes	No	No	No

As nouns, common scoter is a hyponym of scoter; that is, common scoter is a word with a more specific, narrower meaning than scoter:

scoter: large black diving duck of northern parts of the Northern Hemisphere
common scoter: a variety of scoter

Other hyponyms of scoter include Melanitta nigra.

scoter (noun)	common scoter (noun)
large black diving duck of northern parts of the Northern Hemisphere	a variety of scoter