Green monkeys borrow vervet monkeys’ eagle warning call when threatened by drones
Some 40 years ago, scientists discovered that East African vervet monkeys (Chlorocebus pygerythrus) produce distinct alarm calls when they encounter their three main predators: leopards, snakes and eagles. Their cousins in West Africa, green monkeys (Chlorocebus sabaeus), are also known to cry out at the sight of leopard and snakes, but for some unknown reason, they don’t seem to emit a unique call for birds of prey. A team of researchers recently discovered, however, that the sight of a drone prompts green monkeys to emit an alarm call that is strikingly similar to their vervet cousins’ eagle warning—a finding that suggests such vocalizations are evolutionarily “hard-wired,” the researchers write in Nature Ecology & Evolution.
For the new study, the researchers first tried to get green monkeys in Senegal’s Niokolo-Koba National Park to respond to papermaché models of eagles, without any success.
“Perhaps our artwork was unconvincing,” writes study co-author Julia Fischer, a primatologist at the University of Goettingen in Germany. So the team decided to expose the monkeys to drones, an aerial threat that the animals had not encountered before.
Over the course of several months in 2016 and 2017, the researchers conducted drone flights over three different green monkey groups, using audio equipment to record the sounds they made. Each group was exposed to a drone between one and three times.
When they saw the strange flying object, the monkeys emitted a warning call and ran to hide. Upon conducting acoustic analyses of the drone response call, the researchers found that it was distinct from the monkeys’ leopard and snake warning signal. What’s more, the green monkeys’ drone call was remarkably similar to the vervet monkeys’ eagle alarm—a fascinating discovery, given that green monkeys and vervet monkeys diverged from a common ancestor around 3.5 million years ago. Producing the warning call, perhaps, is not a learned response, but a genetically innate one that has been conserved over a lengthy evolutionary history. [Continue reading…]