fauna vs avifauna

fauna and avifauna both are nouns.

Word	Noun	Adjective	Verb	Adverb
fauna	Yes	No	No	No
avifauna	Yes	No	No	No

As nouns, avifauna is a hyponym of fauna; that is, avifauna is a word with a more specific, narrower meaning than fauna:

fauna (noun)	avifauna (noun)
a living organism characterized by voluntary movement	the birds of a particular region or period
all the animal life in a particular region or period