Researchers have found evidence of shared decision-making among a troop of wild baboons, providing insight into how animals that live in socially complex, hierarchical societies reach consensus on decisions that affect the entire group. Until now, researchers had wondered if animals with clear hierarchies, such as primates or wolves, use democracy to reach a consensus - or if their decisions are governed by dominant leaders.

It's been difficult to study this, however, because recording the behavior of many individuals simultaneously has been a challenge, restricting studies of collective animal behavior to species with comparatively simpler social systems. Here, Ariana Strandburg-Peshkin and colleagues leveraged recent advances in global positioning system (GPS) technology to track the movements of baboons.

They fitted 25 wild olive baboons at the Mpala Research Center in Kenya with custom-designed GPS collars and recorded the baboons' locations every second of the day, analyzing the animals' movements relative to one another.

Their data identify certain baboons as initiators - animals that start moving away from other baboons and either "pull" followers with them or "anchor" those individuals in place until the initiator wanders back. Strandburg-Peshkin and her team found that baboons are generally more likely to follow others when multiple individuals act as initiators and agree on a particular direction.

However, when initiators' opinions are split over where to go, decisions get delayed, according to the researchers. Baboons typically don't attempt to negotiate, instead choosing one direction over the other, if the angle between the options is larger than 90 degrees, but the monkeys do attempt to compromise if two initiators suggest different directions with less than 90 degrees difference between them.

These findings suggest that shared, democratic decision-making is widespread even among species with highly stratified social hierarchies. Understanding how groups that exist in such hierarchies reach consensus is critical to understanding the evolution of other socially complex species.

Article #15: "Shared decision-making drives collective movement in wild baboons," by A. Strandburg-Peshkin; I.D. Couzin at Princeton University in Princeton, NJ; D.R. Farine; M.C. Crofoot at University of California, Davis in Davis, CA; D.R. Farine; M.C. Crofoot at Smithsonian Tropical Research Institute in Balboa, Panama; D.R. Farine at University of Oxford in Oxford, UK; I.D. Couzin at Max Planck Institute for Ornithology in Konstanz, Germany; I.D. Couzin at University of Konstanz in Konstanz, Germany.