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Fitbit-wearing baboons reveal price of social cohesion

Baboons can live and travel in troop sizes of up to 150, with smaller baboons speeding up and bigger baboons slowing down to maintain social cohesion. Photo by Carter Loftus/Max Planck Institute of Animal Behavior
Baboons can live and travel in troop sizes of up to 150, with smaller baboons speeding up and bigger baboons slowing down to maintain social cohesion. Photo by Carter Loftus/Max Planck Institute of Animal Behavior

July 27 (UPI) -- As anyone who has ever gone hiking as a family or taken their toddler to the zoo knows, keeping pace and staying together can be a challenge -- it's not much different for baboons.

According to a new study, published Tuesday in the journal Proceedings of the Royal Society B, individual baboons must move at suboptimal speeds in order to maintain cohesion.

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For baboons and other social animals, living and moving together offers advantages. For one, there's security in numbers. But the animal kingdom is full of tradeoffs, and sacrifices must be made to keep the troop together.

Data from Fitbit-like accelerometers attached to members of a baboon troop in Kenya showed the smallest, slowest individuals tend to make the biggest sacrifice, moving at speeds much faster than their preferred pace.

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Senior study author Meg Crofoot has been studying the same baboon troop for nearly a decade, but until recently, researchers didn't have the technology to precisely track the movements of baboons.

"Locomotor capacity clearly governs the way animal societies move, but so far it's been confined to laboratory studies," Crofoot said in a press release.

"The revolution in wearable technology now makes it possible to take locomotion research into the wild," said Crofoot, director of the Ecology of Animal Societies at the Max Planck Institute of Animal Behavior in Germany.

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For the study, scientists affixed GPS trackers and accelerometers to 25 wild baboons in Kenya -- almost the entire troop.

The GPS data, including more than 10 million data points, revealed the troop's broader movement patterns, while the accelerometers recorded the steps taken and speeds achieved by individual troop members.

Researchers used ergonomic data to estimate the preferred gait and speeds of the baboons based on their size. Bigger baboons are able to achiever faster speeds more easily as a result of their longer limbs.

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"The leg is like a big pendulum that you are swinging and that leads to a preferred gait, which translates into preferred speed of movement," said first author Roi Harel, researcher at the Max Planck Institute of Animal Behavior.

The tracking and movement data showed that all members of the troop move at suboptimal speeds. Bigger baboons move at slower than ideal speeds, while smaller baboons move faster than they would prefer.

"The dominant male clearly wields power over other baboons in one-on-one interactions," said Harel. "But when it comes to collective movement, it seems like a shared decision-making process drives the group."

The troop isn't exactly a utopia. The smallest members of the troop have to make the biggest sacrifice, moving at more uncomfortable speeds, to make sure everyone sticks together.

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"This might be because they have the most to gain from group membership," said Harel.

Harel and his research partners used computer models to confirm the significance of these locomotive sacrifices.

The simulations showed that if individuals moved at ergonomically ideal speeds, the troop's cohesion would be quickly lost.

The simulations also confirmed that cohesion was maintained when smaller baboons sped up and bigger baboons slowed down -- the same pattern scientists measured in the field.

In future studies, scientists hope to investigate the ways these ergonomic dynamics might influence the sizes of different groups.

"Maybe the differing locomotor ability of individual animals actually puts an upper limit on how large groups can be. Maybe it forces certain individuals to group together, like mothers caring for toddlers. Maybe it's driving complex organization," Crofoot said.

"Now we have a way of studying locomotion in the wild, we can finally merge this into how we think about the structure of animal societies," Crofoot said.

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