University of Oxford scientists have found evidence that cryptochromes (light-sensitive proteins found in plants and animals) may allow birds them to visually “see” the Earth’s magnetic field.

Cryptochromes are stimulated by blue light at dusk to produce two free radicals. The concentrations of each free radical would be controlled by the Earth’s magnetic field, which is known to vary with latitude. As a result, the radicals would bind in varying degrees with other signalling molecules, depending on how far north or south the animal is.