Visual guidance of bird flight through narrow passages:
We have been examining the visual cues that budgerigars use to fly safely through narrow passages, by filming their flight trajectories when they fly along a tunnel whose walls are decorated with horizontal or vertical stripes.
The results indicate that:
When both walls carry vertical stripes (and therefore present strong image motion cues), the birds fly closedown the middle of the tunnel, i.e. equidistant between
the two walls (center). When one wall carries vertical stripes and the other carries horizontal stripes (which present weak on no image motion cues), the birds fly very
close to the wall that carries the horizontal stripes (left/right). These results indicate that budgerigars negotiate narrow passages by balancing the velocities of image
motion (optic flow) that are experienced by the two eyes.
More information on this ongoing study is available here:
P. Bhagavatula, C. Claudianos, M. Ibbotson and M. Srinivasan (2011)
Optic flow cues guide flight in birds.
Current Biology 21, 1-6.