'avifaunally' ultimately derives from 'avifaunal', which in turn combines the Latin element 'avis' meaning 'bird' and 'fauna' meaning 'animal life' (from Latin 'Fauna').

'avifaunally' developed from the adjective 'avifaunal' (formed from Neo-Latin/modern scientific 'avifauna'); 'avifauna' itself is a modern compound built from Latin 'avis' + 'fauna' and was adopted into English scientific usage in the 19th century.

Originally the components referred to 'bird' ('avis') and 'animal life' ('fauna'); the compound 'avifauna' came to mean specifically the birds of a region, and derivatives like 'avifaunal' and 'avifaunally' retain that specialized sense.