Top panel: the histogram shows the cumulative fraction of the ratio R = ω/ω_self for all edges (blue) and for the edges connecting members of the same cluster from the calibration set (orange). The dashed red line indicates the threshold below which we consider the edge as non-significative and we remove it from the graph. Bottom panel: the histogram shows the cumulative fraction of the ratio between the node degrees after and before the edge breaking. All stars are shown in blue, while members of the calibration set are in orange. The dashed red line indicates the threshold below which we consider the star as “migrator.”