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The magnetic compass of blackcaps sylvia atricapilla






Behaviour 68(1-2): 24-30

The magnetic compass of blackcaps sylvia atricapilla

During autumn and spring migration 1975-1977 the non visual orientation of blackcaps (S. atricapilla) was analyzed. Blackcaps were able to get orientational information from the local geomagnetic field (0.46 Gauss, mN 360.degree., 66.degree., incl. [inclusive]). When magnetic north was turned by 180.degree. to geographic south by reversing the horizontal component of the earth magnetic field, they changed their directional preferences according to this artificial magnetic field (0.46 Gauss, mN 180.degree., 67.degree., incl.). When the horizontal and the vertical components of the magnetic field were reversed (0.46 Gauss, mN 350.degree., -60.degree., incl.), blackcaps had a mean direction which is equivalent to that in the normal earth field. In a partly compensated magnetic field which could not be used for orientation, no significant directional preference was found (0.34 Gauss, mN 360.degree., 60.degree., incl.). Blackcaps were able to get oriental information from the magnetic field-not by the polarity of the magnetic field, but by the interpretation of the inclination of the axial direction of the magnetic field lines in space. They use an inclination compass, as it was described for european robins, to obtain information. During spring migration, the individual test birds showed directional preferences about 180.degree. opposite to the directions they had preferred in autumn. The headings of the individual birds suggest that a mixed population of southeast- and southwest-migrants was tested.


Accession: 006712851

DOI: 10.2307/4533940



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