red grouse vs moorhen

red grouse and moorhen both are nouns.

Word	Noun	Adjective	Verb	Adverb
red grouse	Yes	No	No	No
moorhen	Yes	No	No	No

As nouns, moorhen is a hyponym of red grouse; that is, moorhen is a word with a more specific, narrower meaning than red grouse:

Other hyponyms of red grouse include moorcock.

red grouse (noun)	moorhen (noun)
reddish-brown grouse of upland moors of Great Britain	black gallinule that inhabits ponds and lakes
	female red grouse