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

Birds and other animals, such as fish and turtles, sometimes migrate thousands of miles. They navigate – usually without issue – 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. New research seems to bring the solution one step closer. He suggested that the magnetic sensation of birds migrating like robots might come from light-sensitive proteins in the eyes.

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

Chicken and pigeon

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

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

Research shows that proteins from Robins retina are sensitive to the Earth’s magnetic field. “It’s interesting and well executed,” said David Lintink of the University of Groningen, who studies the way birds move. According to him, this substance is basically a chemical, eating only the particles isolated in a test tube 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 the magnetic sense that migrating birds use to navigate Earth’s magnetic field. The researchers confirmed this in their article.

“A good next step would be to see if this also works for light falling on the retina at night,” Lintink said. Robins are birds that migrate mainly at night with only starlight and moonlight and most of the morning or evening. Next, this research should move from chemistry to biology by studying what happens at the cellular level of the retina and during flight. For although it has been shown in experiments that birds jumping on the ground respond to magnetic fields, in the end it can only be confirmed that they use magnetic senses to navigate if this can be demonstrated during migration.

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