“Why did we fly a drone over green monkeys, one may ask.”
One may indeed. The answer is that Fischer and her colleagues are interested in how primates communicate.
In a classic study back in the 1980s, scientists showed that East African vervet monkeys produce alarm calls that are specific for the predators they encounter. So, for example, vervet monkeys hearing a leopard alarm [clip] might scurry up a tree, whereas the eagle call [clip] sends them running for cover under the closest shrub.
Now, the green monkeys that live in Senegal share a similar system to warn of leopards and snakes. But they aren’t known to raise a ruckus in response to birds of prey.
“And so therefore we decided to fly a drone over them.”
The researchers treated 80 green monkeys to a show of drones. How did the animals react to this unfamiliar aerial intruder?
“The monkeys did respond. They responded with alarm calls. [clip] And they responded by uh running away.”
Here’s where things get really interesting: the calls the green monkeys made after spotting the drones were different from the ones they use to signal leopards [clip] or snakes [clip]. But even more intriguing:
“And when we did an acoustic analysis these alarm calls [clip] were almost eerily similar to the ones of the east African vervets. [clip]”
The findings are described in the journal Nature Ecology and Evolution. [Franziska Wegdell, Kurt Hammerschmidt and Julia Fischer, Conserved alarm calls but rapid auditory learning in monkey responses to novel flying objects]
The fact that the two monkey species seem to speak the same language, if you will, even though they diverged from their last common ancestor some 3 million years ago, suggests that this vocal warning system is hard-wired.
So if you hear a monkey go [clip], watch out for a hungry bird. Or check to see if you got a package delivered.
(The above text is a transcript of this podcast)