Summary
To test the orientation model that the stars derive their directional significance from the magnetic field, the orientation of European Robins (Erithacus rubecula) to an arbitrary pattern of 16 “stars” (Fig. 1) was examined.
Control tests in a magnetic field too weak for orientation, where the birds showed random behavior (Fig. 2), demonstrated that the artificial star pattern by itself did not contain information of the migratory direction. The main experimental series consisted of sets of two tests performed on consecutive nights. In the first tests (N1), the birds were presented the artificial stars together with a magnetic field of adequate intensity and they oriented according to that magnetic field (Fig. 3a). In the second tests (N2), the “stars” remained unchanged (the cage was turned) and the magnetic field was of the same low intensity as in the control series; here the birds continued to show a directional preference that did not differ significantly from the mean of the nights before (Fig. 3 b).
These findings lead to the conclusion that by applying a suitable magnetic field a directional meaning had been given to the 16 “stars”, which allowed the birds to select the same directions as the night before. For this “star orientation” the natural sky could be replaced by a simple pattern of 16 artificial stars, indicating that number, position and configuration of the stars by themselves is meaningless until directional information from the magnetic field has been transferred to them. Thus the findings presented here support the orientation model that the directional significance of the star compass is dependent on the magnetic compass.
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This study was supported by the Deutsche Forschungsgemeinschaft; the computer work was carried out by the Hochschulrechenzentrum of the Universität Frankfurt. We would like to express our thanks to Miss D. Richter, Mrs. H. Theiss-Jahnke and H. Golle for their valuable help in capturing the test birds and conducting the experiments, to W.T. Keeton and F.W. Merkel for critically reading an early draft of the manuscript and especially to S.T. Emlen for many stimulating discussions.
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Wiltschko, W., Wiltschko, R. Interrelation of magnetic compass and star orientation in night-migrating birds. J. Comp. Physiol. 109, 91–99 (1976). https://doi.org/10.1007/BF00663437
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DOI: https://doi.org/10.1007/BF00663437