How baboons decide

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How baboons decide
2 small groups of baboons sit on the ground in Mpala, Kenya.
Seen resting in the shade, this troop of Kenyan baboons was tracked to show the group dynamics related to route choices.
Photo: Rob Nelson

Baboons live in highly structured groups gathering fruits, nuts, even meat. The alpha male gets the females, until he is deposed by a younger competitor. So we were surprised to learn that when they forage across the countryside in Kenya, their decisions are "democratic."

If Roger moves North and Alice moves northeast, Sandra is likely to split the difference, and head north-northeast.

But if Ann joins Roger both move to the north, Sandra will follow them.

If Paul moves North and Jean moves South, Sandra may follow either one.

These results (but not the plain-Jane American names) come from a new study1 of wild baboons, conducted with the help of high-precision GPS collars, by Margaret Crofoot, an associate professor of anthropology at the University of California-Davis.

ENLARGE
Two researchers watch about 12 baboons move up a brushy slope with red gravel underfoot.
Researchers watch the baboon troop forage. About 80 percent of the adults and sub-adults were fitted with high-accuracy GPS collars. Data were collected from 25 individuals, every daylight second for 14 days.
Photo: Rob Nelson
Satellite image of world, with Kenya, Mpala highlighted.

The researchers establish standards for a "pull" (when Clara moves at least 5 meters, and Stephen, nearby, follows) and an "anchor" (when Stephen fails to follow Clara). "Our algorithm looks at the change in distance between two individuals," says Crofoot. "We are looking purely at movement; there is no behavioral data."

We WhyFilers were shocked that the research produced no sign that social status determined who has pull and who doesn’t. According to the authors, "The dominant male did not have the highest probability of being followed, dominance rank did not correlate with initiation success, and no sex differences existed in initiation success.'

When we asked Crofoot, she told us, "Dominance confers first access to food and monopolizes mating access for males, so I was a little bit surprised that we did not find more evidence of a dominant individual using that social power to drive group movement to their advantage.

Previous experiments on primate social decision making were carried out in captivity, she says. "This was the first one in a relevant ecological and social context. Our study highlighted that even if the dominant individual can determine group movement in specific circumstances, most of the time, it's a more democratic process," she added. "As they travel through the habitat … mostly they have an egalitarian, majority rule aspect."

We commented that the baboon behavior seemed highly logical. "Part of what is incredible about this study it that it jibes with the experience we have all had in trying a get a group of people to make a decision when opinions diverge strongly," Crofoot said. "That can stall a group decision so you can't come to any decision, but when the difference between potential choices is small, you can split the difference and push the decision further down the read."

Land Rover in foreground has cables stretching to 3 wire cages in background. About 12 baboons are amidst the cages. 1 cage holds a baboon.
To capture the entire baboon troop, the researchers operated as many as 22 cage traps at once. They hand-triggered the trap doors to avoid recapturing animals that already had a GPS collar, and to ensure that mothers and their offspring were not separated.
Photo: Rob Nelson

Like fish, like birds?

How to Track a Baboon!, a Rob Nelson film

Our conversation was going swimmingly until Crofoot brought up a resemblance to similar decision-making among schools of fish and flocks of birds. Surprisingly, the baboon "results match quite closely with models designed to understand fish movement" Crofoot says. "The majority rules, you split the difference rather than choose between close angles. I was struck by the similarity."

People are a bit more complicated than fish or blackbirds, Crofoot acknowledged. "Human societies have all this stratification, dominance hierarchy, kinship, friendship, various other social relationships, and baboons are a really good system for trying to bridge that gap, because they have dominance, strong kinship, 'friendships' involving preferred social partners."

Think of that before you accuse some bozo of "acting like a baboon."

– David J. Tenenbaum

2

Kevin Barrett, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David J. Tenenbaum, feature writer

Bibliography

  1. Shared decision-making drives collective movement in wild baboons, A. Strandburg-Peshkin et al, Science, 19 June 2015.
  2. More videos like How to Track a Baboon! at Untamed Science