swamphen vs aquatic bird

swamphen and aquatic bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
swamphen	Yes	No	No	No
aquatic bird	Yes	No	No	No

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

swamphen: any of various small aquatic birds of the genus Gallinula distinguished from rails by a frontal shield and a resemblance to domestic hens
aquatic bird: wading and swimming and diving birds of either fresh or salt water

swamphen (noun)	aquatic bird (noun)
any of various small aquatic birds of the genus Gallinula distinguished from rails by a frontal shield and a resemblance to domestic hens	wading and swimming and diving birds of either fresh or salt water