Pigeon homing: Effects of magnetic pulses on initial orientation

After treatment with a 0.5-T magnetic pulse, homing pigeons (Columbia livia) showed headings that deviated from the mean direction of untreated controls. These deflections ranged up to 60 degrees and were most pronounced at distances beyond 100 km from the home loft. When birds treated with a pulse south-anterior and birds treated with south-left were released together, they deviated to opposite sides of the untreated controls, indicating that the direction of the pulse determined its specific effects. On the day of treatment, a south-left pulse caused a significantly larger deflection than a south-anterior pulse. The duration of the effects was not entirely clear; the number of releases with significant deflections seemed to decrease as time passed and birds had made additional homing flights. Our findings agree with the hypothesis that magnetite-based receptors provide the pigeons with orientational information. The manifestations of the effect indicate that the magnetic ''map'' rather than the magnetic compass is involved. Apparently the pulse specifically alters map information.