genus Aepyornis vs bird genus

genus Aepyornis and bird genus both are nouns.

Word	Noun	Adjective	Verb	Adverb
genus Aepyornis	Yes	No	No	No
bird genus	Yes	No	No	No

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

genus Aepyornis (noun)	bird genus (noun)
type genus of the Aepyornidae: elephant birds	a genus of birds