genus Bucephala vs bird genus

genus Bucephala and bird genus both are nouns.

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

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

genus Bucephala (noun)	bird genus (noun)
buffleheads and goldeneyes	a genus of birds