genus Circus vs bird genus

genus Circus and bird genus both are nouns.

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

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

genus Circus (noun)	bird genus (noun)
a genus of haws comprising the harriers	a genus of birds