Birds’ eyes work as a compass

Migrating birds ‘see’ magnetic fields… and scientists now think they know how.

Many birds, such as robins, travel thousands of kilometres during spring and autumn. For years, scientists have thought that they use Earth’s magnetic field to navigate, like having an inbuilt compass, but they weren’t sure how it worked.

Researchers from Germany and Denmark have now identified that the birds probably use a chemical called a cryptochrome (KRIP-toh-krome) to know which way to fly.

A specific cryptochrome, called Cry4, is found in the eyes of birds, amphibians and fish. When light hits Cry4, it reacts differently depending on the magnetic fields around it. The birds can then use this to know if they’re facing the right way. It’s possible amphibians and fish might too.

The scientists also found that migrating birds have a lot of Cry4, while non-migrating birds, such as chickens, don’t.

Because of Cry4, birds can travel across the world – and never have to ask for directions!

This article was published in Issue 25 of Double Helix magazine (https://www.csiro.au/en/Education/Double-Helix). Copyright for this article is held by CSIRO.