A Black Howler monkey

A black howler monkey (Alouatta pigra)

Shutterstock / Ethan Daniels

Black howler monkeys move through their environment using mental maps that they modify and adapt as the landscape changes – a skill previously seen only in humans.

In 2016, Miguel de Guinea at Oxford Brookes University, UK, spent a year in Palenque National Park, Mexico, tracking groups of black howler monkeys (Alouatta pigra) to observe how the primates traverse the complex rainforest landscape.

Tagging the monkeys with GPS tracking technology would have been too invasive, so de Guinea and a group of volunteers had to follow them on foot. “It was a bit exhausting at times,” he says. Tracking the monkeys frequently required the researchers to cross rivers and to climb to the pinnacles of ancient Mayan temples. But the results of their endeavours were surprising.

“We found that the monkeys follow certain routes,” says de Guinea, “but they structure and combine those routes in an efficient, human-like way.”

While most animals move through an environment semi-randomly or by instinct, humans are different. We tend to follow familiar routes encoded in mental maps. We also have a spatial sense of how locations are arranged in the landscape. This means that if an obstacle blocks a familiar path, we can change course – perhaps temporarily switching to another familiar route heading in a different direction – to navigate the obstacle and still reach our desired destination. As de Guinea’s team studied the black howler monkeys, they realised the primates do this too.

For example, the monkeys in the study would always approach favourite fruit trees from the same direction. What’s more, while the monkeys would rarely deviate from established routes, they had no problem doing so if, for instance, a tree forming part of a route had fallen down. In such cases, the monkeys quickly worked out how to connect the broken route to another familiar route, so they could navigate the obstacle and still reach their target.

They could also connect certain routes end to end in order to travel long distances, or they could take shortcuts from one route to another. The way the monkeys would jump from one route to another suggests that they have some concept of how these routes relate to each other in physical space, say the researchers.

In other words, the monkeys can easily amend their route-based view of the world with some knowledge of direction and geography, much like humans do. “It was a big effort,” says de Guinea, “but it was worth it to understand the fascinating cognitive skills that black howler monkeys demonstrate in the wild.”

Journal reference: Journal of Experimental Biology, DOI: 10.1242/jeb.242430

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