]. Stacked space-time density of animal trajectories. a) Space-time cube representation of one month of trajectories of one individual bird. The x-y plane represents geographic space and the z-axis is time (0-24 hrs). b) Brownian stacked space-time density of the trajectories from the space-time cube. c) Gaussian stacked space-time density of the same data and d) isosurface of the highest values in the Gaussian density, indicating a temporal column and a space-time hotspot.