And if the observation of peaceful sheep changes our view of collective animal organization in elephant herds, flock of starlings, grasshopper flight, school of fish? This is the promise contained in an article published on October 20 in Natural Physicswhich models sheep behavior in a new way.

This theory validates several findings, not particularly surprising but for the first time measured by individual monitoring of several herders. First, a flock of sheep “lives” intermittently. It alternates the grazing phase and the movement phase in one file. Over 30 minutes of observation, the researchers observed that the average browsing lasted 2 to 3 minutes, at nearly zero speed, and that movement in a single file, at a rate of more than one meter per second, lasted forty seconds. Then, India’s file leader changed; it is randomly selected. Finally, the direction taken by the leader is also random.

Scenario, equation

There are so many seemingly simple facts, which however cannot be explained by models of interactions between animals… Part of this article is even devoted to pointing out this failure. The old model, for success, since Tamas Vicsek in 1995, describes a collective movement by individuals seeking to match their pace with the average of their peers. If this results in very complex shapes, like a flock of starlings, it fails to create an Indian file, as Panurge, the Rabelaisian character…

Furthermore, this framework assumes that group movement never stops. But clearly, the peaceful sheep did not obey this painstaking rule. “The current model manages to make a change of direction, but in too short a time, which does not match the duration we observed. They do not reproduce the disjointed behavior of the sheep and the leaders do not change.”, slice Fernando Peruani, professor at the University of Cergy-Paris, who later proposed something else. Much simpler.

The sheep, looking down, graze quietly. One of them decided to stop and leave. Another followed, then a third followed the second, and so on. The line is in progress. The leader stopped and the troops started eating again. Then another leader left. Etc.

“By changing leaders regularly, groups demonstrate what is often called collective intelligence. » Fernando Peruani, professor at the University of Cergy-Paris

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