Fig. 4. Whole-night orientation of the 12 pied flycatchers that were tested under a stationary planetarium sky, and whose hourly orientations form the basis for Fig. 5. The birds oriented in a southerly direction, not significantly different from the expected autumn migratory direction. Each dot at the circle periphery indicates the mean orientation of one individual bird. The arrow indicates the group mean vector. The dashed circle indicates the radius of the group mean vector needed for significance (P<0.05) according to the Rayleigh Test of uniformity.