Billions of songbirds migrate every year to different lands thousands of miles away, and the way they reach the exact same place to nest is fascinating and is as if they have precise GPS instruments installed in them.
This mysterious sense of compass direction is due to a ‘magnetic map’ that is very much like the way we use GPS (Cartesian coordinates).
Adult birds develop navigational maps inside them to help them travel to faraway lands. How this happens is still a mystery and various theories are being considered: infra-sound, smells, and gravity variations.
A theory gathering some evidence is that the earth’s magnetic field forms a grid that is followed by the birds.
Studies done on the reed warbler (Acrocephalus scirpaceus), a Eurasian migratory bird, provide clear evidence of the magnetic field.