For a long time, scientists have wondered about how birds manage to navigate in the air over hundreds of miles, sometimes thousands, especially migratory birds. If the theory that the iron present in their beak would serve as a compass has fizzled out, it has been supplanted by another hypothesis: the presence of a protein in their eyes that allows them to see the terrestrial magnetic fields.
This fascinating discovery stems from two scientific studies on European robins and mandarin diamonds (a bird species found in Australia).
The famous protein is called Cry4 and belongs to a class of proteins called cryptochromes. These are photoreceptors sensitive to blue light, found in both plants and animals. These proteins are also involved in the regulation of the circadian rhythm (biological rhythm lasting approximately 24 hours). Recent evidence has shown that cryptochromes in birds’ eyes play a role in their ability to orient themselves by detecting magnetic fields in the Earth. This ability is called a magnetoreception.
The studies have shown that birds are able to perceive these magnetic fields only if certain wavelengths of light are available. In the particular case of the avian magnetoreception, it is especially the blue light which is necessary. All this seems to confirm that it is a purely visual mechanism (based on cryptochromes) that would detect fields thanks to quantum coherence.
It is in order to learn more about these proteins that two teams of biologists have conducted the studies: researchers from Lund University in Sweden studied the mandarin diamonds while researchers from Carl von Ossietzky University in Oldenburg (Germany) studied the European robins.
Lund’s team measured in gene expression three cryptochromes: Cry1, Cry2 and Cry4. They are present in both the brain, muscles and eyes of mandarin diamonds. Their hypothesis is that these proteins associated with the magnetoreception must maintain a constant reception during a day.
They discovered, not surprisingly for circadian genes, that Cry1 and Cry2 fluctuate during the day. On the other hand, Cry4 seems to express at a constant level, which makes it the ideal candidate in the process of magnetoreception.
These findings were supported by the other research, providing the same information. The German researchers found “that Cry1a, Cry1b and Cry2 mRNA have patterns that oscillate strongly in 24 hours, unlike Cry4, which has only a small circadian oscillation”.
On the one hand, the Cry4 protein is concentrated in a region of the retina that receives a lot of light (which corroborates the idea of light-dependent magnetoresponse).
In addition, researchers have also found that Cry4 activity increases in European robins at the time of migration (compared with non-migratory chickens).
Of course, both teams of researchers remain cautious: further research will be needed before stating that Cry4 is the protein responsible for magnetoreception. The evidence collected is strong but not definitive.