Spider monkeys possess a sophisticated social system, sharing “insider knowledge” about the best fruit trees in the forest rather than foraging randomly, new research has found.
Scientists discovered that these primates constantly change their social subgroups, a dynamic behaviour that enables them to exchange vital information regarding food sources.
The study, a collaboration involving scientists from Heriot-Watt University, the University of Edinburgh, and the National Autonomous University of Mexico, was based on seven years of field observations in Mexico’s Yucatan Peninsula.
Researchers utilised this extensive data to explore a key aspect of Geoffroy spider monkey social behaviour, which sees group members frequently split into smaller subgroups before rejoining in different combinations.
The same subgroup might never forage together twice.
Dr Matthew Silk, an ecologist from the University of Edinburgh, said: “It isn’t random social mingling; it’s a clever system for sharing insider knowledge about where the best fruit trees are located across their forest home.
“By constantly changing their subgroups, monkeys who know different parts of the forest can share information about where fruit is available.
“We tracked individual monkeys’ movements and mapped out their core ranges, or the areas each monkey knows well.
“Some parts of the forest are known by multiple monkeys, like a town’s most popular restaurant, while others are known by only one or two monkeys, like a hidden gem.
“There’s enough overlap for monkeys to meet and exchange tips, but enough separation that each monkey scouts different parts of the forest.
“This maximises the whole group’s collective coverage of the best feeding spots.”
Spider monkeys often travel in subgroups of three or more and their ranges also overlap in sets of three or more.
Ross Walker, a PhD student at Heriot-Watt, developed a method based on abstract mathematical theory rather than traditional ecological models which analyse pair relationships.
He said: “We’ve shown that there’s an optimal middle ground between the monkeys sticking together and spreading out too far.
“It’s not helpful if every monkey knows exactly the same thing, and it’s not helpful if no-one ever meets.
“It’s best when individuals explore different areas, but still reconnect often enough to pool what they’ve learned.”
The team used data on a group of Geoffroy’s spider monkeys collected by experienced observers between January 2012 and December 2017.
The species, which is considered endangered, is also known as the Central American spider monkey and the black-handed spider monkey.
Professor Gabriel Ramos-Fernandez, from the National Autonomous University of Mexico, said: “We have shown that the fluid social dynamics of spider monkeys has an important consequence for their foraging success: by exploring their environment in a distributed fashion and then coming together to share their uniquely obtained information, the group as a whole can know the forest better than a single individual could on its own.
“This foraging strategy is a good example of collective intelligence in natural conditions.
“In further work, we would like to use the same mathematical techniques to explore other interactions between more than two individuals, which are very common and understudied.”
The findings are published in the journal npj Complexity.
