In the Blink of Bird’s Eye, a Model for Quantum Navigation | Wired Science | Wired.com
"Many animals — including not only birds, but some mammals, fish, reptiles, even crustaceans and insects — navigate by sensing the direction of Earth’s magnetic field. Physicist Klaus Schulten of the University of Illinois at Urbana-Champaign proposed in the late 1970s that bird navigation relied on some geomagnetically sensitive, as-yet-unknown biochemical reaction taking place in their eyes.

Research since then has revealed the existence of special optical cells containing a protein called cryptochrome. When a photon enters the eye, it hits cryptochrome, giving a boost of energy to electrons that exist in a state of quantum entanglement.

One of the electrons migrates a few nanometers away, where it feels a slightly different magnetic field than its partner. Depending on how the magnetic field alters the electron’s spin, different chemical reactions are produced. In theory, the products of many such reactions across a bird’s eye could create a picture of Earth’s magnetic field as a varying pattern of light and dark."