White storks do not “see” the magnetic field in the sense that we see colors, but they perceive directional information from this field thanks to mechanisms still being studied by researchers. Two main hypotheses coexist, without any being definitively validated for this species.
Two biological avenues under study
The first hypothesis is based on cryptochromes, photosensitive proteins located in the retina of the eye. Under the effect of blue light, these molecules would produce pairs of radicals whose quantum state would be sensitive to the orientation of the Earth's magnetic field. The bird would then perceive a sort of visual pattern superimposed on its normal field of vision, a map of intensity or pattern that would vary depending on the direction of flight. This mechanism, studied in particular in migratory passerines, remains a hypothesis under construction: direct evidence in the white stork is still lacking.
The second hypothesis involves crystals of magnetite, a naturally magnetic mineral, located in the nerve endings of the upper beak, connected to the trigeminal nerve. These particles, on the order of a micrometer, could act as an internal compass detecting the intensity and inclination of the field, providing position information rather than a precise direction. The two systems are not mutually exclusive: they could work in complement, one providing an orientation, the other a position map over long distances.
A crucial sense for a great migratory
This question goes beyond simple biological curiosity: white storks travel thousands of kilometers between Europe and sub-Saharan Africa every year, and Tunisia constitutes a major migration stopover, particularly around the wetlands in the north and center of the country. Reliable orientation, whether based on magnetism, visual landmarks on the ground or the position of the sun, directly determines the success of these journeys. Research on magnetoreception remains an active area of science, with unresolved debates over the exact location of receptors and their relative role in relation to other navigational senses.
