bird of passage vs traveller

bird of passage and traveller both are nouns.

Word	Noun	Adjective	Verb	Adverb
bird of passage	Yes	No	No	No
traveller	Yes	No	No	No

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

Other hypernyms of bird of passage include traveler.

bird of passage (noun)	traveller (noun)
any bird that migrates seasonally	a person who changes location
someone who leads a wandering unsettled life