A little help from your friends can come in handy when you find yourself faced with a foe, and new research published in the journal Royal Society of Open Science has found that some monkeys call for back up, too. Looking at a population of putty-nosed monkeys (Cercopithecus nictitans), the researchers found that females would use specific calls to target just the males, who would swoop in like “hired guns” to get predators of their backs.
The scientific team, in collaboration with the Wildlife Conservation Society's (WCS) Congo Program and the Nouabalé-Ndoki Foundation, looked at 19 different groups of wild putty-nosed monkeys for the research. Each was found within Mbeli Bai, a designated area for study that sits within the forests in Nouabalé-Ndoki National Park, Northern Republic of Congo.
Groups using specific warning calls is commonplace among primates, who have learnt to receive warning calls and respond appropriately, sometimes even picking up on the calls of other species (captive orangutans have even established a new way of communicating not seen in the wild). Among the forest guenons (monkeys from the genus Cercopithecus, including putty-nosed monkeys) males carry some of the loudest alarms but they’re not necessarily more specific than female calls, as a single sound can be used for many functions.
The researchers on this study wanted to experimentally test if sex differences came into alarm call strategies, so they enlisted the help of a “leopard,” a moving model that was convincing enough to make the putty-nosed monkeys think they were under attack. They unleashed the leopard on male and female groups separately, to see how the other monkeys, of a different sex, responded to their calls.
Interestingly, when female monkeys spotted the leopard and raised the alarm, the males would come running but the same effect didn’t happen when it was the males raising the alarm. Before the recruited males knew what was going on, they would make a racket on their approach which the researchers suggest could play a role in establishing the male’s value within the group. The males’ call would then change once they spotted the leopard to a specific anti-predator call, and it was only at this point that the females would stop vocalizing. The different strategies could be tied to the fact that males less involved in such defensive events may get turfed out of the group sooner than those who take the lead, a motivation which may have driven the sex-dependent responses to predators and warning calls.
"Sexual selection might play a far more important role in the evolution of communication systems than previously thought,” said co-author Claudia Stephan of the WCS Congo Program and the Nouabalé-Ndoki Foundation in a statement. “In a phylogenetic context, what strategies ultimately drove the evolution of communication in females and in males? Might there even be any parallels to female and male monkeys' different communication strategies in human language?"
The specific call males made when approaching the leopard was a new one to the researchers, who named it “kek”, which to their knowledge has never before been reported in observational research of putty-nosed monkeys. There are a few reasons why this might be, but it could mean that kek is a population-specific call. If true, it would be an indicator for vocal production learning among these monkeys, a huge scoop for science as it’s widely believed this form of learning doesn’t exist within the animal kingdom.
6
