Contrary to common assumptions, pigeons do not lock their eyes in place during flight. Instead, they make slow, subtle eye movements that may help them gather more information about their surroundings.
That is the key finding of a new study led by Dr. Anthony Lapsansky (AL), who conducted the research as a postdoctoral fellow at UBC, and Dr. Doug Altshuler (DA), professor in the department of zoology. In this Q&A, they discuss what the findings reveal about animal vision and autonomous flight.
Why study homing pigeons?
DA: Pigeons make a good model for research because they're representative of many birds—their eyes are located on the sides of their head, giving them an almost panoramic view of the world. They're also easy to work with, easy to train—and they fly home, so you don't have to worry about losing them.
How did you MacGyver a system to track pigeon flight?
AL: I worked as a falconer before graduate school, so I was familiar with falconry hoods. I sewed many different sizes of hoods to hold the camera in place on the pigeon's head, along with little backpacks for the rest of the equipment, and tried them on the pigeons until I found the perfect fit.
The system weighs just 27 grams and includes a miniature computer, about half the size of a credit card; a tiny modified commercial camera, a motion and orientation measurement unit and cables and electronics tape to reduce static during flight.
We fitted cameras and backpacks onto two pigeons at a time in a flock of about 16, while half wore dummy packs. We released them on a familiar route and I would race them home in my truck to collect the footage.
What did you discover?
AL: When any animal moves through the world, its image of the world moves around it. That can be a really useful signal. When you're walking down a hallway, you know you're centered because both walls move across your retina at the same speed. If you get too close to one wall, that nearby wall appears to move much more quickly.
Many people assumed that birds like pigeons, with eyes on the sides of their heads, would keep their eyes still in flight so that eye movements would not interfere with visual motion caused by flying.
Instead, we found really subtle, slow drifting eye movements as pigeons fly forward. Rather than locking their eyes in place, they compensate for that visual motion with eye movements—potentially to resolve finer details or see features of their surroundings that can aid navigation.
We also found that pigeons turn both eyes inward as they land on a perch. This may enable stereopsis—judging depth by comparing the slightly different view from each eye. Until now, this ability has only been seen in a few birds of prey.
How may this research inform robotic flight?
AL: Many robots and drones have a rigid camera and as the drone flies, the visual motion in the camera tells the drone how fast it is flying, in what direction, and whether or not it is going to hit an object,
Birds use vision to do all these things, but they are also moving their "cameras" to get even more information from the environment. Essentially, things are more complicated than we assumed.
Like birds, humans are highly visual, and this research tells us about basic strategies for extracting visual information for movement that birds and humans have in common. We could potentially use these strategies to make autonomous flying robots or drones more animal-like: more skilled at navigating complex environments and closer to truly autonomous flight.
