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Monkeys in the Costa Rican jungle modify their social behaviours to adapt to the environmental impacts of deforestation, according to research by University of Toronto Mississauga primatologist Laura Bolt and colleagues.

The researchers found that Central American spider monkeys and white-faced capuchin monkeys displayed different social behaviours along the edges of forests compared to interior forest areas.

“One trend we're seeing with primates worldwide is that when their forests are cut down, they're either able to adapt in some way, or their population declines,” says Bolt, an adjunct professor in U of T Mississauga’s department of anthropology.

The findings are detailed in a new study published in the .

Between 2017 and 2023, Bolt and collaborators, who included Professor Amy Schreier at Regis University, studied the social behaviour of monkeys at La Suerte Biological Research Station (LSBRS), located in northeastern Costa Rica and operated by the Maderas Rainforest Conservancy.

The site is an anthropogenically altered tropical rainforest, meaning part of it has been changed by humans. It includes human-altered forest edge areas that are close to clear-cut sites such as cattle pasture or agricultural fields. The site also contains undisturbed interior forest areas.

The team discovered that spider monkeys engaged less in social behaviours overall when living along the forest edge — likely because they had to conserve their energy. 

“Spider monkeys are adapted to be in the highest parts of the canopy all the time when they move. They also prefer to eat specifically lipid-rich fruit like figs, which tend to come from very tall and mature trees,” says Bolt. “In forest edges, trees tend to be a lot smaller. That means spider monkeys can’t find what they need in terms of food, and they don’t have sufficiently tall trees to be able to travel quite as easily. So, they try to use less energy in general when they’re in forest edges.” 

The researchers also found that white-faced capuchin monkeys, which are quite small and vulnerable to predators, engaged in behaviour that wouldn’t draw attention to themselves. For example, these primates vocalized and fought less often while living along the forest edge. 

“If they’re in an area with smaller trees where it’s easier for predators to see them, they’re especially vulnerable,” Bolt says. “It makes sense that the capuchins would try to avoid getting eaten, essentially.” 

Howler monkeys, however, didn’t appear to change their social behaviour along the forest edge — which Bolt says was a somewhat surprising finding. 

In previous research, she and her colleagues found that howler monkeys change how much they eat and travel while living in different forest areas. But past research has also shown that howler monkeys aren’t as adaptable overall when living in different environments.   

“This could be a concern long-term for howler monkeys. They might be only capable of living one way and then they persist until suddenly, they die out because they’re not able to cope,” Bolt explains.  

The study of primates’ social behaviour builds on Bolt’s previous work related to how habitat destruction impacts species on the verge of extinction – for example, ring-tailed lemurs in Madagascar.  

“Studying social behaviour is such a good way of understanding their quality of life, and whether they’re happy,” she says. “Understanding how species behave is a way of better understanding them, and better understanding how to conserve them.” 

Primatology in Costa Rica is at a pivotal juncture, says Bolt, who serves on the board of directors at the Maderas Rainforest Conservancy.

“We wanted to survey them before they’re on the edge of extinction, as a way of maybe informing conservation plans to preserve some of their landscapes.” 

This study was co-authored by former students from around the world who gained experience at the LSBRS field school and returned to continue their research. The primate field school is open to U of T Mississauga undergraduate students as a course credit.