(Covers information from the S.D. Perry novels)
Avis were flying, bat-like BOWs developed by the Umbrella laboratory at the Planet in the American Midwest. They populated the first stage of that facility.
Avis were deployed into the first "stage" of the Umbrella facility called the Planet. Leon Kennedy and John Anders encountered them there, easily making short work of the BOWs before moving on.
Development and Traits Edit
Avis were developed at the Planet facility, probably intended to serve as aerial scouts for either human militaries or other Umbrella BOWs. Although their name is derived from the Latin word for bird (aves), the Planet's staff nicknamed them "Dacs" for their similarity to pterodactyls.
Avis were an extremely delicate BOW, susceptible to just about any kind of conventional firearm, including a 9mm Beretta. The Avis would likely have had to rely on their extreme speed to survive in combat, but the monsters also don't seem to have been especially intelligent. They were highly aggressive, however. It is unknown if the t-virus was used in their creation, and if it was, if they remained a vector.