The protein, called Cry4, belongs to a group of proteins known to regulate circadian rhythms, or biological sleep cycles. It turns out that Cry4 serves a previously unknown function, interacting with light to help birds sense magnetic fields.

Researchers have discovered a protein in birds’ eyes that allows them to see magnetic fields.

“This is an exciting advance—we need more papers like these,” says Peter Hore, a chemist at the University of Oxford who has studied chemical reactions involved in bird navigation.

If the researchers are correct, this would be the first time a specific molecule responsible for the detection of magnetic fields has been identified in animals.

One study involving zebra finches analyzed Cry4 along with the proteins Cry1 and Cry2. The team found that Cry4, unlike Cry1 and Cr2, was produced steadily throughout the day. The researchers pointed out that birds may need to navigate their environment any time of night or day.

Another study, this one on European robins, demonstrated that Cry4 levels were consistent throughout a 24-hour cycle. What’s more, levels increased during the robins’ migratory season, when the birds would need to rely on their navigation skills the most. The team also noted that the location of Cry4 in the retina, an ideal location for an internal compass, provides it with access to a lot of light.

Prior to these studies, scientists thought that birds detected magnetic fields using the iron-rich cells in their beaks. Though the current research isn’t conclusive, it suggests that previous beliefs about avian compasses may have misguided.