Abstract
We have investigated whether, and, if so, how birds use vision to regulate the speed of their flight. Budgerigars, Melopsittacus undulatus, were filmed in 3-D using high-speed video cameras as they flew along a 25 m 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 first 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-specific. It does not rely solely on cues derived from optic flow, but may also be determined by energy constraints.
Highlights
We began by measuring the average flight speed of the birds when they flew through the tunnel when stationary stripes were displayed on both walls (control condition)
When the birds experienced decreased optic flow, there was a significant decrease in the wingbeat duration, i.e. an increase in wingbeat frequency, as well as a decrease in the total number of wing-beats
Our findings reveal that changes of flight speed are elicited only by forward motion of the patterns. This is consistent with the observation that, to a first approximation, the birds display changes in the gross kinematics of their wing movements only when the patterns move in the direction of flight, and not when they move against it
Summary
We began by measuring the average flight speed of the birds when they flew through the tunnel when stationary stripes were displayed on both walls (control condition). The results are summarized, which shows the mean change in flight speed relative to the control (stationary patterns), for each of the six conditions in which the patterns were in motion.
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