Robin “sees” the Earth’s magnetic field with the retina

Birds and other animals, such as fish and sea turtles, sometimes migrate thousands of miles. They navigate – usually without problems – without GPS. Many of them use the Earth’s magnetic field to orient themselves. How they were able to detect this weak magnetic field is still a mystery. The new research appears to bring the solution one step closer. He suggests that the magnetic sensation of migratory birds such as robots may originate from a light-sensitive protein in the eye.

To investigate this, an international group of biologists, chemists, and physicists joined forces. They tested a theory more than forty years old, according to which a light-sensitive molecule interacts with the Earth’s magnetic field via a quantum chemical process. To do this, they looked at a light-sensitive protein called cryptochrome 4 (CRY4) from the retina of European robins. This protein is also found in birds, fish, and other amphibians, which also respond to magnetic fields. their results Wednesday afternoon in nature.

Chicken and pigeons

The researchers isolated the CRY4 protein from robins and showed that it is sensitive to magnetic fields. This works like this: If you shine a light on CRY4, that protein is activated, allowing electrons to jump through the molecule. This arrangement of electrons results in what is called a “radical pair”, that is, two molecules that have an odd number of electrons. These radical pairs are sensitive to magnetic fields. When the magnetic field changes, the radical pairs cause the CRY4 protein to change slightly. Chemists from the research group convincingly demonstrated through their experiments that electrons do indeed jump through the protein, just as theory predicted, and that the radical pairs interact in the presence of a magnetic field.

For comparison, the researchers also looked at CRY4 proteins from chickens and pigeons, which are not migratory birds, but do contain this light-sensitive protein. CRY4 from chickens and pigeons was shown to be much less sensitive to magnetic fields.

The research shows that a protein from Robins’ retina is sensitive to the Earth’s magnetic field. “It’s exciting and well-executed,” says David Lintink of the University of Groningen, who researches the way birds move. According to him, this substance is basically a chemical, eating only the isolated particles in test tubes under artificial sunlight.

Does it work even when very little light falls on the retina of the robin’s eye?

So there is no clear evidence yet that these particles are part of a magnetic sense that migratory birds use to navigate the Earth’s magnetic field. The researchers confirm this in their article.

“A nice next step is to see if this also works for the light that falls on the retina at night,” says Lintink. Robins are birds that migrate mainly at night with only starlight and moonlight and mostly morning or evening. Next, this research will have to move from chemistry to biology by studying what happens at the level of retinal cells and during flight. Because although it has been shown in experiments that birds that jump on the ground respond to magnetic fields, in the end it will only be certain that they use a magnetic sense to navigate if this can be demonstrated during migration.