A quantum trick might be behind birds’ ability to navigate using Earth’s magnetic field lines.

Some researchers think birds might be able to “see” the magnetic field via photosensitive proteins in their retinas. The theory is that when a photon strikes one of these proteins, it creates a pair of oppositely charged ions, which separate for a fleeting moment before recombining. Each of these ions contains electrons with a quantum property called spin. Initially, these spins point in opposite directions – but in a magnetic field, they tend to become aligned. When the ions recombine, this alignment triggers a …