Figure 1. Orientation of European robins, Erithacus rubecula , in the local geomagnetic field; effects of a broadband high-frequency field and of Xylocain, a local anaesthetic, applied to the skin of the upper beak.

Upper diagrams: compass orientation in the migratory direction under 565 nm green light; lower diagrams: fixed-direction responses under a combination of 502 nm turquoise and 590 nm yellow light. The symbols at the periphery of the circle mark the mean headings of the test birds based on three recordings each. Open symbols: when untreated, solid symbols, with high-frequency fields added or with the local anaesthetic applied, respectively. The arrows represent the corresponding mean vectors, and the two inner circles are the 5% (dotted) and the 1% significance border of the Rayleigh test (Batschelet, 1981).