Friday, June 25, 2021

We may finally know how migrating birds sense Earth's magnetic field


23 June 2021
By Clare Wilson

Journal reference: Nature, DOI: 10.1038/s41586-021-03618-9

We may finally know the secret to how migrating birds can sense Earth’s magnetic fields: a molecule in their eyes called cryptochrome 4 that is sensitive to magnetism, potentially giving the animals an internal compass.

The process may result in the animals seeing darker or lighter areas in their vision when they look in the direction of magnetic field lines, says Henrik Mouritsen at the University of Oldenburg in Germany. “You may be able to see where north is as kind of a shading on whatever else you would be seeing.”

Previous work has shown that certain species of birds, such as the European robin (Erithacus rubecula), use Earth’s magnetic fields when they migrate, as well as using visual and other cues. Some European robins migrate south every northern hemisphere winter, for instance from Scandinavia to the UK, and return in spring.

At least part of this ability is thought to lie in their eyes, because their magnetism sensing is disturbed in the absence of light. Mouritsen has previously shown that when birds are using their internal compass, the information is processed in the same parts of the brain that process vision.


Roswitha Wiltschko at the Goethe University Frankfurt in Germany says the case isn’t yet closed because there are other cryptochrome molecules in the eye that could also be responsible for magnetic sensing. “Most cryptochromes would in principle be able to do this,” she says.

And while pigeons don’t migrate, they have been found to be able to navigate using magnetism, suggesting that other cryptochrome molecules may play a role, she says.

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