rare bird vs doer

rare bird and doer both are nouns.

Word	Noun	Adjective	Verb	Adverb
rare bird	Yes	No	No	No
doer	Yes	No	No	No

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

Other hypernyms of rare bird include actor, worker.

rare bird (noun)	doer (noun)
a rare or unique person	a person who acts and gets things done