genus Aythya vs bird genus

genus Aythya and bird genus both are nouns.

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

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

genus Aythya (noun)	bird genus (noun)
canvasback, redhead, pochard, etc.	a genus of birds