Fig. 4

Natural headings of the Great Knots at CMDT before (a) and after sunset (b) and at YLE before (c) and after sunset (d). Each filled dot shows the direction of an individual bird. The average direction (α, arrow at the center of the circle), sample size (n), mean vector length (r, length of the arrow), and p value of the Rayleigh test are indicated. The 95% confidence interval (lines beside the arrow) is presented only when the p value is < 0.05. A dashed line in (c) indicates that the confidence interval is unreliable because of small sample size or low concentration. The mean direction of the sun is indicated by a sun icon, and the migration direction at CMDT and YLE is indicated by a bold arrow outside the circle in each panel