How birds navigate through the sky, e.g. during migration, is a big question. A team of German researchers have tried to answer this question. It seems that birds 'see' magnetic fields via their eyes.
It was already well-known that the earth’s magnetic field plays a role in navigation, but how birds perceive this field was not clear. There are two rival theories on this subject. One theory claims that receptors in the beak play a role. The magnetic compass information is relayed to the brain via the nervus ophthalmicus. Another theory claims that the magnetic field is perceived via photopigments in the eyes and is processed in cluster N, a specialized area in the frontal brain that is night-active.
The researchers from the university of Oldenburg cut the nervus ophthalmicus in one group of robins and they damaged cluster N in another. The robins with a cut nervus ophthalmicus could still navigate using magnetic fields. Those with a damaged cluster N, on the other hand, could no longer navigate on the basis of magnetic fields. They were, however, still able to navigate on the basis of the sun and the stars.
The results of this study were published in the scientific journals Nature and New Scientist.