Homing pigeons navigate like pilots
Homing pigeons navigate in the same classic way as human pilots, by spotting landmarks on the ground, research has shown.
And like their human counterparts, they can be confused by landscape that all looks the same.
The birds are best able to memorise flight paths when the terrain below is neither too featureless nor too crowded.
"We discovered that pigeons' ability to memorise routes is highly influenced by the visual properties of the landscape in a 250 metre radius below them," said lead scientist Dr Richard Mann of Uppsala University, Sweden.
"Looking at how quickly they memorise different routes, we see that that visual landmarks play a key role. Pigeons have a harder time remembering routes when the landscape is too bland like a field or too busy like a forest or dense urban area.
"The sweet spot is somewhere in between; relatively open areas with hedges, trees or buildings dotted about. Boundaries between rural and urban areas are also good."
Dr Mann and colleagues from Oxford University and the Zoological Society of London released 31 pigeons from four sites around Oxford for an average of 20 flights each.
Their findings, published in the Royal Society journal Biology Letters, showed the birds were better navigators over landscapes with a certain visual complexity, such as rural areas with hedges or copses.
Pigeons navigate exceptionally well despite having small brains. Whatever method they use must make highly efficient use of their limited mental processing, scientists believe.
"There may be certain rules that free-flying birds use to structure information that enable them to map the environment using their limited brain power," said co-author Professor Tim Guilford, from Oxford University's Department of Zoology.
"Fundamentally understanding how they do this will tell us more about their abilities and limitations, and could reveal methods that robots with limited processing power might use to navigate."
Knowing the landscape features that pigeons use to navigate could also help researchers to predict the flight patterns of any birds that are active during the day, or diurnal.
Identifying the likely flight paths of birds could be of use to conservationists, birdwatchers and town planners.
"Homing pigeons provide a reliable model for studying navigation and there's no reason to believe that other diurnal birds won't use similar methods," said Prof Guilford.