Fig. 6. Orientation of VIS+ (black lines) and VIS- groups (grey lines) at 1 s intervals after release. Thick lines show r-values (thick broken line indicates critical value for Rayleigh test, 0.5 for N=12 and P=0.050), thin lines show U-test statistic for V-test (thin broken line indicates critical value, 1.64 for P=0.050). For any given group, data are shown until the second when the first bird in that group reaches home.