I caught the end of a television programme in which it was explained that birds are able to sense magnetic forces and that they use these forces as a type of satnav to help them find their way home - and presumably on migration as well. The programme went on to tell that a homing pigeon can sense the forces without using its eyes whereas the robin "sees" the forces through its right eye, its left eye being just a normal eye. Magnets around a bird cause disturbance to its navigation system as they upset the magnetic forces on which the bird relies.
True or not? I really couldn't say.