Vervet monkeys use a clever strategy to outsmart their rivals

Vervet monkeys are clever enough to determine the optimal foraging route that helps them to avoid stronger rivals, according to a new study. The experts found that the monkeys wait until their dominant group mates are too far away to interfere, selecting the shortest route to reach successive food sites and then leisurely snacking at each stop. 

The vervets appear to assess the time that they will have before the more dominant monkeys return, and choose the best route to minimize their travel distance while maximizing food intake. 

Study co-author Dr.  Julie A. Teichroeb is an associate professor in the Department of Anthropology at the University of Toronto Scarborough.

“Here we show that vervet monkeys make foraging decisions that minimize travel time and distance, but also ensure they get access to their preferred food rewards when competitors are present,” saps Dr. Teichroeb.

The results indicate that vervets have the cognitive ability to plan the ideal foraging route according to how much time they have. In humans, such strategies are related to rational thinking. 

The researchers conducted experiments to study wild vervet monkeys in central Uganda. The experts were able to distinguish between 44 individuals based on their faces, fur color, and other natural markings.

“In previous work we have shown that vervets faced with a similar foraging problem immediately rush for preferred food sites when a competitor is present, but take the route that minimizes travel distance between food sites when foraging alone. In this feeding array, that would be to start at the nearest platform, then move along the outside of the array and only take the banana when it was encountered,” explained Dr. Teichroeb.

“However, the large sample size in the present study allowed us to show that vervet foraging decisions were much more complex than the above simple dichotomy.”

The vervet monkeys selected the route that minimized travel distance when no group mates were near. When the stronger rivals were nearby, the monkeys quickly assessed the risk of competition and modified their route. 

“When the competitor was at the array with them at the onset of the trial, the vervets took the hurried solution and immediately rushed to the banana, retrieving and eating it quickly. They also made a beeline for the banana when there was a high risk of competition,” said study first author Dr. Jean Arseneau-Robar.

“This was the case if the dominant had short travel distance to travel time, or if the focal vervet was unskilled at retrieving the banana. But if the latter had a bit more time, he or she would stop to eat from a corn platform en route to the banana.”

Adults males who outranked the other members of the group did not bother to assess which food sites to visit, as they did not have to worry about competition.

“The adult males only needed to decide which food patches they wanted, and which patches they would let other group members have,” said Dr. Arseneau-Robar.

According to Dr. Teichroeb, the findings show how incredibly complex foraging decisions can be in vervet monkeys. 

“Decision-makers are taking in a lot of ecological and social information, while also considering their own current food-handling skill, and synthesizing this all very quickly before executing their route decision. And they are very good at making the best decisions, as they manage to get their preferred food in the vast majority of cases, even when under pressure.”

The study is published in the journal Frontiers in Ecology and Evolution.

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By Chrissy Sexton, Earth.com Staff Writer