Physics research shows that sheep herds alternate their leader and achieve collective intelligence

Credits: Luis Gómez-Nava, Richard Bon and Fernando Peruani.

The collective movement of animals in a group is a fascinating subject of research for many scientists. Understanding this collective behavior can sometimes inspire the development of strategies for promoting positive social change, as well as technologies that mimic nature.

Many studies describe swarming behavior as a self-organized process, where individuals in a group continually adjust their direction and speed to eventually achieve “collective” movement. However, this perspective fails to take into account the hierarchical structure of many animal groups and the potential benefits of a “leader” who leads the way.

Luis Gómez-Nava, Richard Bon and Fernando Peruani, three researchers at the Université Côte d’Azur, Université de Toulouse and CY Cergy Paris Université recently used physics theory to investigate the collective behavior of small herds of sheep. Their findings, published in nature physicsshow that by alternating between the roles of leader and follower, the herd eventually achieves a form of ‘collective intelligence’.

“In most herd systems, collective movement is not a continuous process, but occurs in episodes: for example, collective movement phases are interrupted to rest or feed,” Peruani told “Nevertheless, most collective movement studies, including experimental and theoretical, consider groups to remain in motion from start to finish. In addition, it is often assumed that herd behavior requires individuals to continuously negotiate the direction of travel.”

The main goal of Peruani and his colleagues’ recent work has been to investigate the collective movement of an animal system in a way that explicitly takes into account the temporal aspect of the observed self-organized process, specifically that collective movement phases have a beginning and an end. to have. . In addition, the team wanted to adopt an alternative and holistic perspective, which views the animal group’s movement as a collection of “collective phases.”

“From this perspective, questions about the mechanisms of information exchange and consensus decision-making take on a new dimension,” explains Peruani.

In their experiment, Peruani and his colleagues closely studied the spontaneous behavior of small groups of sheep over different time intervals. They analyzed the trajectories of individual herd members and calculated the animals’ overall spatial arrangement and orientation, while also assessing correlations between the speed at which individual animals moved.

“We first showed that none of the existing flow models, or extensions of them, are consistent with our observations,” Peruani said. “We then analyzed how information travels through the group, identified an interaction network that is consistent with the data, and examined what information is transmitted over this network.”

Research shows that sheep herds alternate their leader and achieve collective intelligence

Credits: Luis Gómez-Nava, Richard Bon and Fernando Peruani.

Interestingly, Peruani and his colleagues found that the interaction network that reflects the behavior of the herds they observed was highly hierarchical. In addition, they showed that the only information disseminated through this network is information pertaining to the position of the sheep within the group.

Using their findings, the researchers built a model of animal collective movement that focuses on two key cognitive processes. These processes are the selection of a leader who will lead the herd for a period of time and the mechanism underlying the herd’s navigation.

“Importantly, each collective movement phase has a temporal leader,” Peruani explained. “We investigated the mathematical properties of the resulting model to identify the benefits of the revealed collective strategy. I believe the main contribution is the following: the animals, by using a hierarchical interaction network to move together for a while , you give full control of the group to the temporary leader, but there is also a rapid turnover of temporary leaders.”

Essentially, the researchers’ findings suggest that sheep alternate between the roles of leader and follower as they move in herds. So leaders only lead the group for a certain amount of time, before control of the group is transferred to another sheep.

“If a temporary leader has knowledge relevant to the group (for example, the way out of a maze or the location of a food source), then the temporary leader will be able to efficiently guide the group,” Peruani said. “In this way, all group members benefit from that knowledge. It is worth noting that this only works if all individuals follow the temporary leader without question.”

The findings collected by Peruani and colleagues shed new light on the dynamics underlying the collective movement of small flocks of sheep. However, to investigate to what extent these findings can be generalized, further experiments with larger herds and different animals will have to be performed.

“We wondered: If there is a temporary leader at any given time, how does the group share and process information that each individual member of the group has? Can the group pool information to enhance its ability to accurately navigate to a distant place? In short, does the group exhibit collective intelligence?” Peruvian said. “We have proven that by regularly changing the temporary leader, the group is able to pool information and demonstrate collective intelligence.”

Overall, the recent work of this team of researchers highlights the possibility that some naturally occurring collective animal strategies take advantage of both hierarchical and democratic organizational schemes. In the future, their observations could inspire new studies exploring the physics and biology underlying these intriguing collective animal behaviors.

“We are now investigating collective movement using groups of different agents,” Peruani added. “In particular, we compare the spontaneous behavior of groups of lambs, young sheep and adult sheep to examine whether sheep learn to follow temporal leaders and behave as one over time. We also examine how groups behave in complex environments such as mazes or arenas with different food spots that can create a conflict of interest within group members. And more broadly, we investigate how collectives distribute and process information, using various statistical mechanical tools.”

More information:
Luis Gómez-Nava et al, Intermittent collective movement in sheep results from alternating the role of leader and follower, nature physics (2022). DOI: 10.1038/s41567-022-01769-8

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