To test whether the sun is an essential factor for the development of a functioning orientation system in birds, a group of young pigeons was raised as ‘No-Sun’-birds. They were not allowed to see the sun, and they were released to fly around their loft only under total overcast. The control group had an equal number of opportunities to fly under overcast plus additional flights under sun.
When released as untrained birds under solid cloud cover, the ‘No-Sun’-birds were significantly oriented, whereas the controls were not. Small magnets glued between the wings (north toward the head) reversed the ‘No-Sun’-birds' orientation, indicating they used a magnetic compass.
These findings show that the orientation system can develop without information from the sun. Differences in the orientation behavior of the ‘No-Sun’-birds and normally raised young pigeons are discussed.