The mystery behind how birds navigate might finally be solved: it's not the iron in their beaks providing a magnetic compass, but a newly discovered protein in their eyes that lets them "see" Earth's magnetic fields.
These findings come courtesy of two new papers - one studying robins, the other zebra finches.
The fancy eye protein is called Cry4, and it's part of a class of proteins called cryptochromes - photoreceptors sensitive to blue light, found in both plants and animals. These proteins play a role in regulating circadian rhythms.
There's also been evidence in recent years that, in birds, the cryptochromes in their eyes are responsible for their ability to orient themselves by detecting magnetic fields, a sense called magnetoreception.
We know that birds can only sense magnetic fields if certain wavelengths of light are available - specifically, studies have shown that avian magnetoreception seems dependent on blue light.
This seems to confirm that the mechanism is a visual one, based in the cryptochromes.