R. Soc. Open Sci. 2, 140355 (2015)

The graceful movements of animal collectives such as flocks of birds and schools of fish have long been studied by scientists interested in animal behaviour. Although the fundamental question of interest is ultimately about their evolutionary origin, significant strides in understanding their mechanistic origin in different species have been made by borrowing techniques from statistical mechanics. For example, it is now established that information such as a change of direction is effectively transmitted through the entire animal aggregate simply as a response mediated by nearest-neighbour interactions between individual animals — a process that is superficially similar to the many-body effects present in simple magnetic systems.

However, the seemingly instant reactivity of animal collectives to predatory attacks — such that they turn in unison to produce so-called escape waves — has so far eluded a simple description. Now, James Herbert-Read and colleagues have addressed this issue by studying the response of fish schools to simulated predatory attacks. They found that escape waves are initiated by individuals changing direction in response to a change in their neighbours' speed. This speed-based mechanism was confirmed numerically, and may explain how escape waves can propagate without centralized control.