genus Rhea vs bird genus

genus Rhea and bird genus both are nouns.

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

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

genus Rhea: type genus of the Rheidae; large tall flightless South American birds similar to but smaller than ostriches
bird genus: a genus of birds

genus Rhea (noun)	bird genus (noun)
type genus of the Rheidae; large tall flightless South American birds similar to but smaller than ostriches	a genus of birds