Internal Clocks and Homing

After the documentation of “Zeitgedachtnis” in bees about thirty years ago [1], twenty more years elapsed before the unique role of chronometry for orientation was recognized with the discovery of the sun compass in a series of arthropods [2, 3] and birds [4, 5]. However, the only thing rendered possible by a compass is direction finding. While this mechanism met ecological requirements of numerous arthropods and explained many of their habits, it did not sufficiently elucidate the phenomenon of navigation, e.g., birds homing over wide ranges of unknown territory. Although a series of observations and of field experiments with wild birds had provided evidence for the prevalent role of direction finding in migration [6], there was no evidence of the nature of the mechanism, that is, whether the sun compass or any chronometry at all was employed in the navigation of birds. A rather sophisticated capacity for chronometry and...