Together with an international team of scientists, he investigated another sense birds can use to help them—the earth’s magnetic field. And the most likely molecule is the protein cryptochrome. Intagliata: But here’s what they didn’t know: How does that light-sensitive protein, cryptochrome, actually help the birds sense magnetic fields? That, in turn, might trigger a cascade of messaging, which would allow the bird to “sense” the magnetic field. [Jingjing Xu et al., Magnetic sensitivity of cryptochrome 4 from a migratory songbird]This experiment only tested the proteins outside birds’ eyes.