ptarmigan vs red grouse

ptarmigan and red grouse both are nouns.

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

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

ptarmigan: large Arctic and subarctic grouse with feathered feet and usually white winter plumage
red grouse: reddish-brown grouse of upland moors of Great Britain

Other hyponyms of ptarmigan include Lagopus scoticus, moor-bird, moorbird, moorfowl, moorgame.

ptarmigan (noun)	red grouse (noun)
large Arctic and subarctic grouse with feathered feet and usually white winter plumage	reddish-brown grouse of upland moors of Great Britain