dark-eyed junco vs snowbird

dark-eyed junco and snowbird both are nouns.

Word	Noun	Adjective	Verb	Adverb
dark-eyed junco	Yes	No	No	No
snowbird	Yes	No	No	No

As nouns, snowbird is a hypernym of dark-eyed junco; that is, snowbird is a word with a broader meaning than dark-eyed junco:

dark-eyed junco: common North American junco having grey plumage and eyes with dark brown irises
snowbird: small North American finch seen chiefly in winter

Other hypernyms of dark-eyed junco include junco.

dark-eyed junco (noun)	snowbird (noun)
common North American junco having grey plumage and eyes with dark brown irises	white Arctic bunting
	small North American finch seen chiefly in winter
	medium-sized Eurasian thrush seen chiefly in winter