Pineal Body and Bird Navigation: New Experiments on Pinealectomized Pigeons

and Summary Three series of experiments were performed with pinealectomized homing pigeons released under sun. In the first series, birds were not subjected to further treatments; their homing behaviour turned out to be scarcely or not at all impaired. In the second series, birds were kept in an oscillating magnetic field before release. The same deflecting effect of the treatment was observed in both control and operated birds; this shows that the pineal is not involved in this magnetic effect and adds to the evidence contrary to a role of the pineal in processing magnetic information for navigational purposes. In the third series, birds were kept in continuous dim light (DD) or in artificial light dark cycles (LD) for three or five days before the test. In intact birds in DD, free running of the circadian rhythm which controls the sun compass was observed. The rhythm of pinealectomized birds turned out to be entrainable to light‐dark cycles, as birds in LD were capable of homeward orientation. Operated birds in DD, on the contrary, performed poorly in orientation; also their homing success was impaired. Therefore, the pineal body turns out to act as a pacemaker for the circadian rhythm controlling the sun‐compass orientation.