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Video abstract for the article 'The origin of traveling waves in an emperor penguin huddle' by R C Gerum, B Fabry, C Metzner, M Beaulieu, A Ancel and D P Zitterbart (R C Gerum et al 2013 New J. Phys. 15 125022). Read the full article in New Journal of http://iopscience.iop.org/1367-2630/15/12/125022/article, and see the Supplementary Videos in the special playlist below. GENERAL SCIENTIFIC SUMMARY Introduction and background. The emperor penguin (Aptenodytes forsteri) is the only vertebrate species that breeds during the severe conditions of the Antarctic winter. To conserve energy, they form densely packed huddles with a triangular lattice structure. Video recordings from previous studies revealed coordinated movements in regular wave-like patterns within these huddles. It is thought that these waves are triggered by individual penguins that locally disturb the huddle structure, and that the traveling wave serves to remove lattice defects and restore order. The mechanisms that govern wave propagation are currently unknown, however. Main results. Here we present a model to address the origin and mechanism of the traveling wave. The equations describing the penguin motion are similar to those used for traffic systems. When a penguin moves forward, it pushes the penguins in front and pulls the penguins behind, which in turn start to move. This movement spreads through the entire huddle as a wave. The model recapitulates key experimental findings: traveling waves maximize the density of the huddle, lead to an overall locomotion of the huddle, and allow for merging of huddles. Furthermore, the model predicts that any penguin within the huddle can trigger such a wave, which is confirmed by video recordings that show waves starting at different positions within the huddle. Wider implications. Our extension of conventional traffic models provides insights into the mechanism by which penguins dynamically organize their huddle structure and solve the conflicting aims of mobility and high packing density.