greater scaup vs Aythya marila

greater scaup and Aythya marila both are nouns.

Word	Noun	Adjective	Verb	Adverb
greater scaup	Yes	No	No	No
Aythya marila	Yes	No	No	No

As nouns, greater scaup and Aythya marila are synonyms defined as:

greater scaup and Aythya marila: large scaup of North America having a greenish iridescence on the head of the male

greater scaup (noun)	Aythya marila (noun)
large scaup of North America having a greenish iridescence on the head of the male	large scaup of North America having a greenish iridescence on the head of the male