What navigation ability lets migratory birds sense Earth’s magnetic field?

Magnetoreception is the ability that lets migratory birds detect and use Earth’s magnetic field for navigation.

Many migratory birds appear able to sense magnetic direction as part of a wider navigation system. They also use landmarks, the Sun, stars, smells, and inherited route information. Magnetic cues are particularly valuable when birds travel over oceans or through unfamiliar landscapes.

Research suggests that birds may receive magnetic information through light-dependent processes in the eye and through magnetic particles in tissues, although the exact biological mechanism remains an active research subject. Different species may use more than one magnetic-sensing system.

Magnetoreception is not the same as a built-in map that gives a complete route. Young birds can combine inherited directional tendencies with environmental cues, while experienced adults may refine navigation through learning and prior journeys.