Social waves are hallmarks of animal aggregations. Besides giant honeybees, which display shimmering waves in response to wasps, birds and mammals [4]–[6], [12], social waves have also been described for avian flocks [24], [29], [37], [40]–[45], for the huddles of Emperor penguins [30], and for aggregations of humans in football stadiums [15]. A main question concerning social waves is whether they are advantageous for the aggregation, having received evolutionary function and conveying fitness benefits, or alternatively, whether they are simply a mere epiphenomenon of reactivity