Fig. 25

Distance between selected origin and midpoint between the eyes for the obstacle avoidance flights, in the direction perpendicular to the headpack’s plate. We selected three frames in which the bird’s sagittal plane was almost parallel to the camera plane. We then estimated on each of them the real length of the yellow segment (the approximate distance from the headpack’s baseplate to the bird’s eye), based on the known length of the green segment (the height of marker 1 above the baseplate). We obtained a mean value of 17.3 mm