Migratory orientation of pied flycatchers: interaction of stellar and magnetic information during ontogeny

Abstract

To study the interaction between magnetic compass and star compass during ontogeny, young pied flycatchers, Ficedula hypoleuca, were hand-reared, and after becoming self-sufficient were transferred into outdoor aviaries with full view of the sky. They were divided into three groups: controls experienced the sky while sitting in the local magnetic field; for group WSW, magnetic north was turned by 120 ° anticlockwise to geographical west-southwest; and for group ESE it was turned 120 ° clockwise to eastsoutheast. The birds remained in the aviary until the onset of the migratory season. They were then transferred indoors and tested in the local geomagnetic field without access to celestial cues. The controls showed a significant preference for the seasonally appropriate migratory direction. The group WSW was significantly oriented with a mean 119 ° clockwise from that of the controls. This is in agreement with the hypothesis that celestial cues during the pre-migratory period override any innate magnetic information and establish a new compass course with respect to the magnetic field. The orientation of the group ESE was significantly more scattered, and the mean does not fit the hypothesis mentioned above. Possible reasons for this difference in behaviour are discussed. If it reflects a true asymmetry of the orientation system, the sense of rotation of the sky, being an asymmetric factor, might be involved in the sense that a transfer of information from one system to the other might occur more easily in the direction of rotation than against it.