A new study is exploring the way language has evolved. Researchers from the German Primate Center (DPZ) - Leibniz Institute for Primate Research are examining how West African green monkeys react to unknown sounds as part of a study on language evolution.
Previous studies have shown that East African vervet monkeys warn their fellow animals about predators with special alarm calls that mean "leopard," "eagle" or "snake."
The researchers looked at the closely related West African green monkeys in their own examination.
The researchers flew a drone over the group and later played them the sound of the drone from a recording. By observing the monkeys, it was determined that the animals learn very quickly what the drone noise means.
Borrow words to extend the language
The monkey group did not create a new alarm call for the new sound though instead adopted a call that the East African vervet monkey uses to warn against aerial predators like eagles.
This initial research suggests to the research group that the vocal call structure is closed having been established long ago in the course of evolution.
The East African vervet monkeys have three main enemies: leopards, eagles, and snakes. The monkeys have a specific warning call for each of these potentially dangerous animals. Each call is accompanied by a specific protective action that is undertaken by individual monkeys when they hear the call.
For example when the call for "leopard" is made other monkeys in proximity climb a tree, when they hear the call for "eagle," they search the sky and hide, and when the call for "snake" is uttered, they stand on two legs and remain motionless.
Look and listen
West African green monkeys also have alarm calls for leopards and snakes, but they do not have a sound for skyborne enemies. Julia Fischer from the German Primate Center led the new research into the alarm call system.
The aim of the drone research project was to determine how quickly the monkeys could learn the meaning of new sounds.
Fischer and her team confronted a group of West African green monkeys occur near the DPZ research station Simenti in Senegal with a drone flown over the group at the height of 60 meters. When the sound was played back to the monkeys later they responded with alarm calls, and some even searched the sky and hid.
These alarm calls differed a lot from the sounds the animals made in the presence of snakes and leopards; however, they did resemble the alarm calls that East African vervet monkeys produce when an eagle approaches from the air.
"The animals quickly learned what the previously unknown sounds mean and remembered this information," says Julia Fischer, head of the Cognitive Ethology Laboratory at the German Primate Center and lead author of the study.
"This shows their ability for auditory learning." The scientist have concluded that alarm calls are deeply rooted in the broader evolution of the vervet monkeys