If you’d looked to the skies in Oxford, UK, during the summer of 2016 you could have been forgiven for thinking you had spotted the world’s first bionic pigeons.
The birds in question would have been members of a very special cohort trained to wear custom-designed head sensors to track how they navigated using eye movements. The results are now revealed in a study published in the Journal of Experimental Biology.
Because pigeons’ eyes are fixed, they monitor their surroundings mainly by moving their head, according to lead researcher Fumihiro Kano from Kyoto University in Japan. Indeed, 90% of pigeon gazes are accompanied by head movements.
This means that head movement can be used as a proxy for where they are looking, and hence provide clues to their behaviour.
“Eyes are the window to the mind,” Kano says, explaining that gaze tells us a lot about how animals behave and think about the world.
For many years, he has been studying emotion and cognition in great apes (including bonobos, chimpanzees, orangutans and gorillas), Japanese monkeys, human infants, children and adults.
In 2016, he and colleagues published a study showing that apes understand when beliefs are false.
For his latest project, he thought it would be interesting to record gaze in free-moving animals, teaming up with primate biologist Dora Biro from the University of Oxford, UK, to do so.
Homing pigeons (Columba liviai) were ideal species to test in motion because they tolerate wearing custom-made masks and sensors on their head and fly back to the home loft so the data can be retrieved.
It took Kano three months to develop the special mask. Every day he rummaged through a local craft store, experimenting with different materials to create something that fitted to the pigeon’s head as stably and comfortably as possible.
The result was a device hand-made with cloths, wires and elastic bands, which he stitched and soldered together himself.
“The most important thing was to design the mask so that it did not interfere with the bird’s breathing when flying,” he explains.
The pigeons were habituated to the head units, which were continually modified until they were comfortable and the researchers were satisfied the birds could walk, take off, and fly normally while wearing them.
The masks bore an inertial measurement unit to track the bird’s head movements using a gyroscope, accelerometer and magnetometer. The pigeons also wore tiny backpacks containing a state-of-the-art GPS tracker, microcomputer and battery.
Altogether, 22 birds were released from a novel site for 172 solo flights, followed by 172 paired flights and 44 repeated solo flights.
The team was delighted with the outcome. Kano says the birds’ heads were extremely stable during the flights, and the data showed every detail of their movements as well as the GPS recording of the return path.
During solo flights, the pigeons undertook detailed scanning of the landscape, moving their heads “far more than necessary for manoeuvring flight,” says Kano.
When they approached landmarks such as a main road and railway line – linear structures that pigeons tend to use for constructing routes – they reduced their head movements, suggesting “that they indeed ‘see’ them to navigate.”
When they were flown in pairs, they reduced their head movements, “indicating that the flock-mate is a key visual cue that they need to pay attention to,” Kano says.
He suggests the method could be applied to understanding how pigeons use attention in the natural environment, and even to develop bio-inspired drones. Next, the team is keen to add a tiny camera into the sensor to get a bird’s eye vista of the world.
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