marsh hen vs Fulica americana

marsh hen and Fulica americana both are nouns.

Word	Noun	Adjective	Verb	Adverb
marsh hen	Yes	No	No	No
Fulica americana	Yes	No	No	No

As nouns, marsh hen and Fulica americana are synonyms defined as:

Other synonyms of marsh hen include American coot, mud hen, water hen.

marsh hen (noun)	Fulica americana (noun)
any of various small aquatic birds of the genus Gallinula distinguished from rails by a frontal shield and a resemblance to domestic hens	a coot found in North America
a coot found in North America