Spider monkeys use collective wisdom to find more food

A new study from the Santa Fe Institute (SFI) is describing how spider monkeys create dynamic foraging teams to collectively gain a better understanding of their environment. The researchers found that the monkeys exploit the knowledge of their teammates to make informed decisions.

The study was focused on wild spider monkeys in a protected area near Punta Laguna, Mexico, who live in a fission-fusion society. With this type of community, the composition of the social group changes over time. The animals merge into a group for sleeping and other activities, but split up into small foraging teams during the day.

“By forming these subgroups – constantly coming together and splitting – the spider monkeys develop a more thorough knowledge of their environment,” said study lead author Gabriel Ramos-Fernandez of the National Autonomous University of Mexico.

‘They seem to be pooling information about resources, so that as a group they know their environment better than any individual does on its own.”

Over two years, the research team recorded the interactions of 47 monkeys for five hours per day. Ramos-Fernandez said that the monkeys, which are accustomed to being observed by people, typically formed subgroups of two to 17 animals. However, these subgroups only stayed together for one to two hours. “We noted who was where, and with whom, at any given time.”

According to the observations, the monkeys make individual choices on how long to stay on a foraging team and when to switch to another. This behavior produces a range of foraging team sizes.

The researchers teamed up with computational experts at SFI to investigate how the monkeys collectively compute team sizes by using an approach called inductive game theory.

“This kind of methodology is useful for studying optimal foraging because it requires no a priori assumptions about benefits and costs,” said Ramos-Fernandez. 

The analysis revealed that a monkey’s decision to stay with or leave a foraging team was influenced by the decisions of their teammates. This behavior indicates that spider monkeys take into account the opinions of others on optimal team size and use those opinions to inform their own choices. 

The collective decisions ultimately produced a range of team sizes that worked well given the availability of fruiting trees in the monkeys’ forest, even though the team sizes were not a perfect match. 

The research has implications for understanding the behavior of other collective systems, including flocks of birds or groups of fish.

The study is published in the journal Frontiers in Robotics and AI.

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By Chrissy Sexton, Earth.com Staff Writer