How do migrating birds find their way?

Migration relies on redundancy rather than a single sense. Birds carry a magnetic compass, calibrate direction from the sun's position with an internal clock to correct for its movement, learn star rotation patterns as nestlings to find true north, use olfactory maps in some species, and follow coastlines, rivers, and mountain ranges. Experiments displacing birds hundreds of miles off course have shown that adults can correct and reach their destination while first-year birds often continue on their original heading, indicating that young birds inherit a direction and duration while experienced birds acquire an actual map.

The magnetic sense is the most striking finding. The leading explanation involves cryptochrome proteins in the retina that undergo quantum-level changes in the presence of a magnetic field, which would mean magnetic direction appears as a visual overlay, and supporting evidence includes birds needing certain wavelengths of light for their compass to work. A second mechanism using magnetite particles may detect field intensity, contributing map information rather than direction. Practical implications follow: light pollution disorients night migrants and causes mass collisions with lit buildings, which is why Lights Out programs in major cities measurably reduce deaths, and radio-frequency noise has been shown in controlled experiments to disrupt the magnetic compass entirely.