… A team looking at Campbell’s monkeys (Cercopithecus campbelli campbelli) in the Ivory Coast’s Tai National Park … studied alpha males in six wild groups. These monkeys do not play a very social role but are alert to potential threats and disturbances and use their calls to highlight them.
The researchers discovered that the monkeys made several distinct alarm cries, among them calls described as “boom”, “krak” and “hok”.
The team found that booms were sounded when a falling branch had been spotted or to initiate group travel.
Kraks were only given after a leopard had been sighted.
While hoks were almost exclusively sounded when a crowned eagle swooped above the canopy.
But further analysis revealed that while booms were always unaltered, the monkeys sometimes added an “oo” to their kraks and hoks – and this transformed the information they were conveying.
Klaus Zuberbuehler, an author of the paper from the University of St Andrews, Scotland, said: “If you add this subtle additional oo unit to turn krak into krak-oo, then that call can be given to a whole range of other contexts. If you take the suffix away then it is almost exclusively a leopard alarm call.”
While krak-oo appeared to be a general alarm call given to almost any disturbance, hok-oo was used for commotion specifically in the canopy, from the presence of neighbouring groups of monkeys to a glimpse of other flying animals.
Professor Zuberbuehler added: “What is interesting is that the same acoustic modifier is being used for these calls and that is really analogous to using a suffix in human language.” …