SHORT-TERM EFFECTS OF HORIZONTAL GEOMAGNETIC FIELD DEFLECTIONS ON THE ORIENTED BEHAVIOUR OF CAGED ROBINS, ERITHACUS RUBECULA (L.)

SUMMARY Single specimens of the European robin, Erithacus rubecula (L.) were placed in a small, L-shaped cage with two arms of the same length, pointing 45° to the left and right of natural North. Pairs of Helmholtz coils around the cage could generate deflections of the horizontal geomagnetic component 45° to the left or right of natural North, thus making it coincide with one of the arms of the cage. Intensity and inclination were unaffected. Birds were subjected to magnetic treatments lasting 2 min for one bird and 8 min for the other four birds used, in which one of the two magnetic deflections was provided. The two types of treatment were given in succession, and repeated several times in each experiment, according to a randomized schedule. Bird displacements were automatically recorded, and the total times and numbers of separate periods of time spent in the two arms of the cage were computed. The percentage tendencies towards one and the other arm were evaluated from these data, and analyzed to see...