Green monkeys have a special call to warn others a drone is nearby imageBROKER/Alamy Stock Photo

How do you teach a monkey new tricks? Lab trials have proved difficult places to train monkeys to distinguish between sounds and take different actions in response.

But in the forests of Senegal’s Niokolo-Koba National Park, researchers were astonished at the speed one species of monkey adapted its behaviour to a new sound.

Julia Fisher and her team flew drones over one community of green monkeys (Chlorocebus sabaeus) in the area, to see what they made of a new flying object in their environment. They responded instantly, making alarm calls to warn one another of the prospect of a new threat.


The vocalisations were distinct from the ones they made in response to models of leopards and snakes, but almost identical to calls made by a related species of monkey in response to eagles. The results suggest a hard-wired response to the perception of an aerial threat and the use of that specific call.

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The monkeys adapted so quickly to the new noise that they began scanning the skies and making the calls even when played a sound of the drone from the ground.

The monkeys were never seen issuing alarm calls to birds of prey in the area, suggesting the birds they usually see are not considered a threat. The drones, however, seemed to be perceived as dangerous.

“It’s certainly disconcerting, unpredictable, something they’ve not seen before, so it makes sense to alert everybody,” says Fisher.

The dangers of holding a leopard model

She says she was “blown away” by how rapidly the monkeys appeared to learn. “The listeners are smart. It’s almost impossible to get a monkey in a lab to do an audio task.” It is not clear why such learning is harder in a lab environment, she says.

The study involved a year’s worth of fieldwork by a team of eight, who flew the drone about 60 metres above the monkeys. The research wasn’t without incident. Fisher had to duck inside a hide made of palm leaves at one point, after a baboon – which are known to attack leopards – came running to attack the leopard model she was holding.

Vervet monkeys (Chlorocebus pygerythrus) in East Africa, which are related to green monkeys, have been closely studied for the different calls they make in response to a variety of predators including pythons, leopards, baboons and martial eagles.

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The expectation for the green monkey study was they would either stay silent, come up with a new alarm call or come out with one like the vervet monkey eagle call. Fisher’s bet was on the latter, and she was proved right. The vocalisation was highly conserved by evolution.

“It teaches us about how different their vocal communication system is from ours. On the production side there is a very limited level of flexibility,” says Fisher.

Journal reference: Nature Ecology and Evolution, DOI: 10.1038/s41559-019-0903-5