There are several versions of the Birdy frame, Birdy 1 with frame made of aluminum tubes, Birdy 2 monocoque, Birdy 2 World also frame made of aluminum tubes and Birdy 3 monocoque (+ a Birdy 3 with frame made of tubes, 3 generations of limited series Titanium Birdy and an hydro-formed frame P40 limited series not commercialized by Riese & Müller so not officially commercialized in Europe and US).
The geometry and feeling given by these several versions is quite different.