'avifaunal' originates from Neo-Latin, specifically the word 'avifauna', where 'avis' meant 'bird' and 'fauna' referred to 'animal life'.

'avifaunal' changed from the Neo-Latin word 'avifauna' with the English adjectival suffix '-al' added to form the modern adjective 'avifaunal'.

Initially it referred to the noun 'avifauna' (the bird life of a region), but over time it evolved into the adjectival sense 'relating to birds' now expressed by 'avifaunal'.