You may know the Fitbits as handy little doo-dads strapped onto wrists that help people chart their fitness, but now a Fitbit-style device (an accelerometer) is being used to unveil the secrets of group cohesion in baboons.
Researchers from the Max Planck institute of Animal Behaviour, Germany, sought to understand the costs and benefits of moving in groups. To do this, they attached accelerometers to a troop of baboons moving through the wild, as detailed in a new study published in Proceedings of the Royal Society B.
Group living is a common feature among all sorts of animals, including many of our primate cousins. The benefits of group living include protection from predators and the teaching of skills, but there can be associated physical costs, too.
“Anybody who has tried to walk with a toddler knows the challenges of moving with someone who has a different physical ability,” says first author Roi Harel, “but cracking open this mystery in wild animal groups required technology to catch up.”
Baboons, according to the study authors, live in societies of up to 150 individuals, ranging from 30kg adult males to infants, and they travel in mixed-age groups. To understand how members of the group adjust their speed to suit the collective, the researchers attached GPS trackers and accelerometers (like Fitbits) to 25 wild baboons at the Mpala Research Centre in Kenya.
The GPS data showed where the animals moved, while the accelerometers gave high-resolution information about movement including speed and number of steps.
The researchers found that while all members of the group adjust their preferred speed to some degree to match the collective, the littlest members footed the greatest energy bill, exerting themselves to keep up with the rest.
“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,” says Harel. But, despite having a preferred speed, all the animals in the group adjusted their speed to match the animals near to them. The researchers credit this to democratic processes unusual in an extremely hierarchical species.
“The dominant male clearly wields power over other baboons in one-on-one interactions,” says Harel. “But when it comes to collective movement, it seems like a shared decision-making process drives the group.”
Harel suggests the smallest animals may pay the highest cost because they have the most to lose from a lack of group cohesion, being vulnerable and juvenile.
Senior author Meg Crofoot, director of the Ecology of Animal Societies at the institute, has been studying this particular troop since 2012, but says this new study is a first for animal movement research.
“Locomotor capacity clearly governs the way animal societies move, but so far it’s been confined to laboratory studies,” she says. “The revolution in wearable technology now makes it possible to take locomotion research into the wild.”
The team hopes the study will help direct future research into the movement of socially cohesive animals through their natural environments.
“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 organisation?” poses Crofoot.
“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.”