When baboons travel, majority rules

Baboons don’t follow the leader. When a troop of these monkeys splits up and starts moving in two dramatically different directions, animals gravitate toward the more popular choice, a new study finds.

When traveling baboons branch off in only moderately conflicting directions, the animals compromise by taking an in-between path, say quantitative and computational biologist Ariana Strandburg-Peshkin of Princeton University and her colleagues.

Democratic styles of group decision making based on simple rules occur even in complex animal societies, such as those of baboons, the researchers conclude in the June 19 Science. Previous research has found that simple rules for responding to neighbors’ behavior also explain movements of bird flocks and fish schools (SN Online: 7/31/14).

“Decisions about the day-to-day movements of baboons’ lives are made via a very egalitarian process, despite a stratified social structure,” says study coauthor Margaret Crofoot, an anthropologist at the University of California, Davis.

High-ranking baboons control access to food and mates, among other perks. But there are reasons for troop movements to take a democratic turn, Crofoot says. Dominant males, for instance, often guard sexually receptive females and don’t focus on the troop as a whole.

The researchers analyzed the movements of 25 olive baboons (Papio anubis) in a troop of 29 individuals for 14 consecutive days. The animals ranged freely in a savanna near a research center in Kenya and wore custom-designed GPS collars that constantly recorded their locations.

Certain animals tended to move away from the troop and attract followers, but those trailblazers weren’t dominant individuals. Males and females who struck out on their own were equally likely to be followed.

If the angle between diverging paths was greater than 90 degrees, baboons chose one direction over another based on majority rule. For smaller angles between travel options, troop members compromised.

GPS tracking is a new addition to studies of wild baboons. In Strandburg-Peshkin’s investigation, this technology revealed relatively quickly and persuasively that baboon troops move in the direction that has the most support, remarks behavioral ecologist Andrew King of Swansea University in Wales. King and his colleagues are using GPS collars to study baboons in Namibia and South Africa.