Eine Analyse des Orientierungsverhaltens nachtziehender Vögel im Merkel-Wiltschko-Käfig

Zusammenfassung

Untersucht wird das Verhalten von 3 nachtziehenden Vogelarten imMerkel-Wiltschko-Käfig als Käfig für Orientierungsversuche nach dem Magnetfeld und dem Sternenhimmel. Neben der Übereinstimmung der ermittelten Laborzugrichtungen mit den Literaturdaten entspricht auch das Aktivitätsverhalten dem natürlichen Zugzeitverhalten. Eine Korrelation der Richtungswahlen mit der Aktivität, der Konzentration der Richtungswahl und der Anzahl der Kreisflüge war nicht möglich. Künstliche Magnetfelder riefen eine „Streßreaktion“ bei den Versuchsvögeln hervor: starke Erhöhung der Aktivität und der Anzahl der Kreisflüge, wobei die Orientierungsleistung erhalten blieb. „Nicht-orientierte“ Vögel wiesen in den Einzelnächten eine höhere Vektorlänge und eine niedrigere Aktivität auf als diejenigen im natürlichen Erdmagnetfeld. Aufgrund der unterschiedlichen Aktivitäten und Vektorlängen wird vermutet, daß der Herbst- und Frühjahrszug von unterschiedlichen Faktoren beeinflußt wird. Die durchführbare Verhaltensanalyse erlaubt es, imMerkel-Wiltschko-Käfig gezielt die Auswirkung einzelner Faktoren (z. B. Temperatur, Wind, Luftdruck usw.) auf die Orientierung zu überprüfen. Unterstützt wird das natürliche Verhalten des Vogels in dem Versuchskäfig durch die Möglichkeit einer dem Ruderflug ähnlichen Bewegung.

Summary

Two different cages are used for orientation tests:Emlen funnels andMerkel-Wiltschko-cages. Most of the orientation tests with migrating birds were performed inMerkel-Wiltschko-cages. In this paper I analyzed the activity behaviour of Blackcaps, Lesser Whitethroats and Robins at orientation tests inMerkel-Wiltschko-cages during autumn and spring migration. The orientation behaviour of these night-migrating birds was tested with reference to the dependence on different magnetic field conditions and on an artificial starry sky. The following results were obtained: 1. Blackcaps and Robins are able to get orientational information from the local geomagnetic field, but Lesser Whitethroats are totally disorientated in this test condition. 2. When magnetic N was turned by 180° to geographic S by reversing the horizontal component of the earth magnetic field Blackcaps changed their directional preferences according to this magnetic field. 3. When the horizontal and vertical components of the magnetic field were reversed they had a mean direction which is equivalent to that in the normal earth field. 4. In a partly compensated magnetic field which could not be used for orientation no significant directional preference was found. 5. In an artificial earth magnetic field and with artificial stars robins are able to obtain orientational information by the magnetic field and by star patterns. — The analysis of the orientation behaviour in theMerkel-Wiltschko-cage showes that it is impossible to point out a correlation between activity, the vector length and the amount of circling in the test condition in the geomagnetic field. But in test conditions with artificial magnetic fields there were strong correlations. The birds reacted on these artifical magnetic fields with a higher activity and a higher amount of circlings but the plotting of the night migration direction was not influenced. I interpret this behaviour as a stress reaction on these artifical magnetic fields produced by Helmholtzcoils. The distribution of the headings of the single test night was more concentrated during autumn than during spring migration. But in the single test night the vector length of the mean direction was higher during spring than during autumn migration. An interpretation of these facts may be given by the glacial periods or by the food shortage at wintertime. Therefore in autumn the birds had to fly by the straightest way to their winter ground. At spring they can remove behind the receding winter. The analysis of the orientation data obtained in spring migration revealed a strong correlation between orientation behaviour, temperature and pressure. The analysis showes that theMerkel-Wiltschko-cage is a very good orientation cage to test birds which live in bushes. In this test cage the birds keep up their normal migratory behaviour. An other advantage is that single external factors can be tested under laboratory conditions in this cage.