Figure 4. The light-dependent magnetosensor involves the antennae.

(a) Fall migrants that were oriented equatorwards during their initial flight (left; red; n=5) had significantly less directional flight (that is, Z<500) when both antennae were painted black during their second flight (right; black; n=5). (b) In contrast, fall migrants that were directed towards magnetic South during their initial flight (left; red; n=5) shifted towards magnetic North when tested with clear-painted antennae under reversed inclination angle conditions (right; grey; n=5). For both a and b, monarchs (left diagrams; red) were tested in a generated field with a 45° inclination angle and an intensity of 141 μT. In contrast, monarchs (right diagrams; black for a and grey for b) were tested in a generated field that had the same intensity, but where the inclination angle was −45°. In both a and b, each bar graph indicates the mean Z±s.e.m. score of animals for each group. Each circular diagram consists of the group orientation behaviour for each group in which each monarch plotted (dot) had a Z score >500. For each circular diagram, the arrow indicates mean group orientation, shaded area is 95% confidence interval, and mN is magnetic north.