subgenus Chen vs bird genus

subgenus Chen and bird genus both are nouns.

Word	Noun	Adjective	Verb	Adverb
subgenus Chen	Yes	No	No	No
bird genus	Yes	No	No	No

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

subgenus Chen (noun)	bird genus (noun)
wild goose having white adult plumage	a genus of birds