The mechanisms which allow a carrier pigeon to find its way in space are not yet fully understood. Researchers continue to study them to unlock their secret. This article takes stock of the state of knowledge.
It is a reality: even placed in an unknown place, the pigeon is able to find its way back to its loft. The ability of carrier pigeons to find their way back, even though they are several hundred kilometers from their place of origin, with precision and speed, has never ceased to intrigue humans. Sun, stars, terrestrial magnetic field, smells… It would be the crossing of several data captured by the pigeon which would allow it to locate itself in space. But more concretely?
The memory of pigeons
The brain of a pigeon has a neuron density six times higher than that observed in the human brain. The average distance between two nerve cells is 50% shorter than in humans. Thus, the pigeon processes information faster and proves capable of complex cognitive functions, even in the absence of a complex cerebral cortex. Experiments were carried out to reveal the pigeon’s learning capacities, hitherto unsuspected: learning basic numerical rules, memorizing 4-letter words …
However, this memory does not seem to be able to be at work to allow the pigeons to return to their loft when the birds are released in a place they have never seen before, and therefore could not memorize. . The researchers believe, however, that their memory allows them to create the equivalent of a mind map where the position of the Sun during the day and the stars at night play an essential role.
The visual abilities of pigeons
Pigeons have been trained to detect cancer cells on biopsy images. Indeed, they have visual skills superior to those of humans. Color perception is linked to eye photoreceptors called cones. When the human being has 3 types which perceive the 3 primary colors (cyan, yellow, magenta), the pigeons have the same ones plus a fourth. They are tetrachromates. This type of additional photoreceptor allows them to distinguish ultraviolet rays that are invisible to our eyes. A pigeon can therefore differentiate between objects which appear to us to be identical in color. Hence the idea of employing them in laboratories to perform tasks requiring expensive training of medical technicians. And it is probably this additional sensory faculty that allows them to use the Sun and the stars to find their bearings in space.
Smell in pigeons
Italian and New Zealand researchers wanted to know if the pigeon uses its sense of smell to orient itself. Inexperienced pigeons, without training, were used for the experiment. Half of the pigeons had their olfactory nerve cut, thus depriving them of the sense of smell, and the other half the trigeminal nerve, associated with sensitivity to magnetism (see next paragraph). Some of the birds were released 50 km north of Pisa, another 50 km south. As a result, all pigeons with the severed trigeminal nerve returned, except for one, when only one-sixth of the birds with the severed olfactory nerve returned. While the first had taken 24 hours to return, the others had taken one more day.
Magnetoreception of pigeons
The pigeon would be equipped to perceive the earth’s magnetic field and use it to locate itself in space. To confirm this hypothesis, a study carried out in the 1970s consisted of attaching a magnet to pigeons. Thus, as a magnet disturbs a compass which then no longer indicates magnetic North but the place where the magnet placed nearby is located, the pigeon is unable to return to its loft.
The principle of terrestrial magnetism is based on the core of the planet, located more than 3000 kilometers below the earth’s surface. It is made up of 85% molten iron which generates small electric currents that create the magnetic field. If humans don’t feel it, some animals, like pigeons, do. It is called the magnetoreception. Carrier pigeons are not the only animals with a magnetic navigation system. All migratory birds, but also bees, dolphins, sea turtles and even certain bacteria can also orient themselves in this way.
In pigeons, this sensitivity was attributed to the trigeminal nerve by Dr. Wild. Pigeons are found to be very sensitive to magnetic field anomalies caused by unusual geological formations or solar magnetic storms.
Sensitivity to Earth’s Gravity
Gravity is not strictly equal everywhere on the surface of the Earth because it results from the distribution of masses on the surface but also in depth. A researcher from Zurich wanted to know if pigeons could also use Earth’s gravity to find their way around. It is a crater 25 km in diameter located in Ukraine that was chosen as the place of experimentation. The dovecote was located 91 km from where the birds were released. A control group was released at an equivalent distance but outside the crater. If the second found their way in a predictable way, the first took detoured paths, far from the shortest path, thus showing that gravity had to play a role in the pigeons for spatial spotting. However, the principle of the mechanism remains unknown.
Spotting carrier pigeons in space: unknowns persist
In addition to the deepening of spatial identification via terrestrial gravity, there are still many unknowns to be resolved. The study carried out in the 1970s jointly tested the identification by the terrestrial magnetic field that of visual cues. Indeed, if the pigeons carrying a magnet were disoriented in bad weather, they were no longer so in good weather, with the exception of inexperienced young birds.
Thus, researchers do not yet have a perfectly clear idea of how carrier pigeons find their way in space. How are these different types of tracking organized? Would tracking in connection with the Earth’s magnetic field be a back-up when weather conditions do not allow us to base ourselves on visual or olfactory cues? Is sensitivity to terrestrial magnetism innate and is the visual and olfactory navigation system acquired through experience? There is no doubt that this research subject will not be exhausted and that the future will provide us with answers.