[During autumn and spring migration 1975-1977 the non visual orientation of Blackcaps (Sylvia atricapilla) was analysed. The following results were obtained : I. Blackcaps were able to get orientational information from the local geomagnetic field (0.46 Gauss, mN 360°, 66° Incl.). 2. When magnetic north was turned by 180° 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°, 67° Incl.). 3. When the horizontal and the vertical components of the magnetic field were reversed (0.46 Gauss, mN 350°, -60° Incl.), Blackcaps 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 (0.34 Gauss, mN 360°, 60° Incl.). The observed behavior indicates that Blackcaps are 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- and that they use an inclination compass, as it was described for European Robins. During spring migration the individual test birds showed directional preferences ca. 180° opposite to the directions they had prefered in autumn. The headings of the individual birds suggest that a mixed population of SE- and SW-migrants was tested., During autumn and spring migration 1975-1977 the non visual orientation of Blackcaps (Sylvia atricapilla) was analysed. The following results were obtained : I. Blackcaps were able to get orientational information from the local geomagnetic field (0.46 Gauss, mN 360°, 66° Incl.). 2. When magnetic north was turned by 180° 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°, 67° Incl.). 3. When the horizontal and the vertical components of the magnetic field were reversed (0.46 Gauss, mN 350°, -60° Incl.), Blackcaps 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 (0.34 Gauss, mN 360°, 60° Incl.). The observed behavior indicates that Blackcaps are 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- and that they use an inclination compass, as it was described for European Robins. During spring migration the individual test birds showed directional preferences ca. 180° opposite to the directions they had prefered in autumn. The headings of the individual birds suggest that a mixed population of SE- and SW-migrants was tested.]