Research reveals that birds use optic flow cues to guide flight

20 Oct 2011

The beauty and majesty of birds in flight has long captured the attention of artists and photographers.

Now QBI researchers have unlocked the secrets of how birds avoid collisions as they soar, swoop, dive, glide and engage in other aeronautic manoeuvres.

The grace of birds in even cluttered environments is all a function of their perception of something called optic flow, says lead researcher Dr Partha Bhagavatula.

“Our findings show, for the first time, that birds regulate their speed and negotiate narrow gaps safely by balancing the speeds of image motion, or optic flow, that are experienced by the two eyes,” says Dr Bhagavatula.

In order to undertake the study, researchers trained budgerigars to fly through a seven-metre corridor.

Researchers then lined the corridor with different combinations of thick black horizontal and vertical stripes and filmed the budgies’ flight trajectories.

They found that birds flew down the centre of the corridor when optic flow cues were balanced (with identical, vertical stripes on either side of the corridor) but flew closer towards one wall or another when these cues were unbalanced (such as when one wall was lined with horizontal stripes and the other with vertical stripes).

The birds also flew faster when the tunnels were lined with horizontal stripes (rather than vertical stripes), indicating that they were using optic flow cues to regulate their flight speed.

Dr Bhagavatula explains that because the birds naturally flew in a horizontal direction within the tunnel, horizontal stripes (parallel to the direction of flight) would provide only weak motion cues, whereas vertical stripes (perpendicular to the direction of flight) would provide strong motion cues.

Although similar flight behaviours have previously been demonstrated in honeybees, bumblebees and flies, this is the first time that the use of optic-flow signals has been demonstrated in birds.

The findings, which were published in the latest issue of Current Biology, suggest that some of the principles that underlie visually guided flight may be shared by all diurnal flying animals, says Professor Mandyam Srinivasan, head of the laboratory.

According to Professor Srinivasan, who is a Queensland Smart State Premier’s Fellow and a member of the Australian Research Centre of Excellence in Vision Science, these findings also have important implications for robotics.

For example, the speed, agility and accuracy with which birds fly through a thicket of branches can teach scientists a lot about designing vision systems for guiding autonomous aerial vehicles through densely cluttered environments.


Denise Cullen
Executive Communications Officer
Phone: +61 7 3346 6434

Professor Mandyam Srinivasan
Group Head, QBI
Mobile: +0434 603 082

Dr Partha Bhagavatula
Postdoctoral Fellow, ANU/NVRI
Mobile: +0437 399 481


Visual and Sensory Neuroscience laboratory

The goal of our laboratory is to understand how vision guides and shapes behaviour. Finely-tuned behaviour is critical the survival of any species, and this competition for survival promotes the evolution of better visual systems. This is readily apparent to anyone observing a bird achieving a collision-free flight through a dense forest, a bee orchestrating a smooth landing, or a president ducking to evade a flying shoe. Today’s robots perform such tasks with far less finesse. Our mission is to better understand how the eye and brain solve complex visuomotor tasks, and to ask if this understanding can be used to design novel strategies for machines that see, perceive, steer and navigate.

Queensland Brain Institute

The Queensland Brain Institute (QBI) was established as a research institute of the University of Queensland in 2003. The Institute is now operating out of a $63 million state-of-the-art facility and houses 33 principal investigators. QBI is one of the largest neuroscience institutes in the world dedicated to understanding the mechanisms underlying brain function.