How birds avoid crashes 'unlocked'

Washington, Oct 28 (PTI) The secret of how birds manage to zip flawlessly through narrow spaces without crashing into obstacles has finally been unlocked by scientists, led by an Indian-origin researcher. Prof Mandyam Srinivasan from the Vision Centre and colleagues at University of Queensland have found birds weave rapidly and safely through dense forests and narrow corridors by using their eyes to sense the speed of background image flow on both sides and adjust their flight according to it. They say the discovery can be used to design bird-safe urban structures and improve versatility of pilotless planes. As animals travel forward, things that are close seem to speed by, and things that are farther away seem to travel more slowly. It's the same for birds. We found that they try to achieve a safe 'balance' by ensuring that the background images are passing at the same speed in both eyes. This means that if the bird flies closer to obstacles on one side, the near eye will see things passing by faster while those seen by its other eye will pass more slowly. This imbalance prompts the bird to veer away to even out the speed of image flow in both eyes, Prof Srinivasan said. To find out how birds navigate through narrow passages and away from danger, the research group trained budgerigars to fly along a corridor with walls lined with horizontal or vertical stripes. We found that birds fly the fastest when both walls are lined horizontal stripes, because the stripes are parallel to the bird's flight direction, and the birds don't 'see' a strong image flow in the background. But when both walls have vertical stripes, birds slow down significantly due to the strong image motion, which shows that birds also regulate their flight speed according to what they see, Dr Partha Bhagavatula, a team member, said. When the walls were set up with different orientations -- one with vertical and the other with horizontal stripes, the group found that birds flew significantly closer to the horizontal stripes. Prof Srinivasan says that flight behaviour in birds is very similar to insects such as honeybees, bumblebees and flies: This suggests that this principle of visual guidance may be shared by all day-active flying animals. Furthermore we believe these findings can contribute to the technology of guiding unmanned aerial vehicles where aircraft have to fly through obstacles in cluttered environments, or through canyons and gorges or under bridges. PTI MOT MOT 10281108