ShuiEro ... from vague up to sometimes ;) crystal clear drop by drop ...

We have investigated whether, and, if so, how birds use vision to regulate the speed of their flight.
Budgerigars, Melopsittacus undulatus, were flmed in 3-D using high-speed video cameras as they
flew along a 25m tunnel in which stationary or moving vertically oriented black and white stripes
were projected on the side walls. We found that the birds increased their flight speed when the
stripes were moved in the birds’ flight direction, but decreased it only marginally when the stripes
were moved in the opposite direction. The results provide the frst direct evidence that Budgerigars
use cues based on optic flow, to regulate their flight speed. However, unlike the situation in flying
insects, it appears that the control of flight speed in Budgerigars is direction-specifc. It does not rely
solely on cues derived from optic flow, but may also be determined by energy constraints.