Assembly of the Birds is not a named poet. This site attaches the heading to a short Imperial lyric on a Cairo papyrus (P.Cairo inv. 67860), the copy dated around the second or third century CE. Heitsch prints the Greek; the Latin heading Conventus Avium is a later editorial name.
What this site holds is that papyrus lyric of bird-song for Zeus’s ear.
Papyrus, not a medieval book.
Available Works
Fragments on Birdsong
Ἀποσπάσματα περὶ Ὀρνίθων ᾠδῆς
1 passages
Also published as PDF.