Figure 1

Orientation of robins during spring migration. Compass orientation was recorded under 502 nm turquoise light and the 'fixed direction' response under a combination of 502 nm turquoise and 590 nm yellow light. The triangles at the periphery of the circle indicate the mean heading of individual birds based on three recordings each, the arrows represent the grand mean vectors in relation to the radius of the circle = 1, with the two inner circles representing the 5% (dotted) and 1% significance border of the Rayleigh test [17].