ptarmigan vs moor-bird

ptarmigan and moor-bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
ptarmigan	Yes	No	No	No
moor-bird	Yes	No	No	No

As nouns, moor-bird is a hyponym of ptarmigan; that is, moor-bird 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
moor-bird: reddish-brown grouse of upland moors of Great Britain

Other hyponyms of ptarmigan include Lagopus scoticus, moorbird, moorfowl, moorgame, red grouse.

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