Fig. 4

Releases under the dome and artificial sky in the morning (A, D), mid-day (B, E), and afternoon (C, F). A–C, blue filter plus grey filter in the eastern half of the artificial sky. D–F, A–C, blue filter plus grey filter in the western half of the artificial sky and the polarizing filter in the opposite area. The dashed line shows the separation between the grey and the polarizing filter. Each dot represents the direction of one sandhopper; the arrow in each distribution represents the mean vector. The mean angle is also given together with its confidence limits. The black triangles external to the distributions represent the geographic direction of the sea at the home beach. The white triangles indicate the expected direction based on the visual stimuli of the artificial sky. n, number of radially orientated individuals; nt, total number of released sandhoppers. The values of the Rao’s spacing test U, with the probability level P are also given