The word "bird" is used for the HUD speed vektor indicator and inputs are then inertial.
Airbus tried to create illusion of HUD but the "bird" of the AF447 A330 was only a F/D variation and inputs came from the ADIRU alimented by airflow. It is why their "bird" disappeared as written in ACARS. Example of bad copy from the Viper by A...
The FBW Airbus' bird looks like, smells like, but is not HUD
