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Female putty-nosed monkeys get their males to run defense against predators

A female putty-nosed monkey Image by C Kolopp / WCS.

  • A new study found that female putty-nosed monkeys use alarm calls to recruit males to be their “hired guns” when a predator is detected, only stopping their vocalizations once males have been enlisted to ward off the threat.
  • Recruited males will vocalize their participation with a “pyow” call, which may aid their reproductive chances in the future, according to the study.
  • The researchers also observed that male putty-nosed monkeys emitted a newly described “kek” call when responding to a simulation of a leopard moving along the forest floor.
  • The researchers say that this study, as well as related studies, can aid conservation efforts for the putty-nosed monkey, a near-threatened species, and broaden our understanding of communicative and cognitive capacities of non-human primate species.

Female putty-nosed monkeys know what to do when they detect a leopard. They chirp out an alarm call to the males, essentially recruiting them to be their “hired guns.” In response, the males approach the group while making “pyow” sounds, demonstrating their commitment to serve as bodyguards, and possibly enhancing their reproductive opportunities, experts say. It’s only after the males spring to action that the females stop calling.

Researchers with the Wildlife Conservation Society’s (WCS) Congo Program and the Nouabalé-Ndoki Foundation observed this behavior in putty-nosed monkeys (Cercopithecus nictitans) across 19 different groups in Mbeli Bai, a swampy forest within Nouabalé-Ndoki National Park in northern Republic of Congo. They recently published their findings in Royal Society Open Science.

“What was surprising … was to find that females and males have very different strategies to use their alarm calls, with females manipulating male behavior to defend them and their offspring, and with males advertising their commitment for predation defence and actively mobbing the predator away,” study co-author Claudia Stephan, a scientific consultant at WCS, told Mongabay in an emailed statement. “It’s like evolution led to the same vocal output in females and in males, namely calling in the presence of a threat, but for at least partly different reasons.”

Male putty-nosed monkeys have been observed to make different calls depending on the predator or situation. For instance, males will make the “pyow” sound when a terrestrial predator, such as a leopard (Panthera pardus), is detected in the area, and a “hack” sound when the predator is a crowned hawk-eagle (Stephanoaetus coronatus). But the researchers also identified a new type of male alarm call, referred to in the study as a “kek.” Males made this sound when a member of the research team donned leopard-print fabric and skulked along the forest floor.

“Whether this call is specifically emitted to moving threats on the ground … or whether kek calls are an expression of population dialects remains to be investigated,” Stephan said. “A vast variety of animal species throughout very different phylogenetic branches use different calls in very different contexts like when facing a danger, during reproduction, in food-related situations or during other social events.”

Liesbeth Sterck, a primate expert and behavioral biologist at Utrecht University, says a nice finding of the study is that female monkeys cease their calling once they enlist the help of the males, but become more persistent in their alarm calling when they can’t recruit any males.

However, she says the study lacks behavioral descriptions of the putty-nosed monkeys reacting to predators. For instance, the study says the females and their offspring hide from predators once the males have been recruited, but this behavior isn’t fully described, Sterck says. There is also no description of what males do when they spot a predator while away from the group, she adds.

“There’s data lacking, and it might be because it’s too difficult [to observe] with unhabituated groups,” she said.

Study coauthor Frederic Mehon (right), and his guide, Lazard Libanga (left) during data collection. The leopard model is visible in the background. Image by Claudia Stephan / WCS.

The putty-nosed monkey, which is a type of forest guenon, is a near-threatened species that is vulnerable to bushmeat hunting, habitat loss through deforestation, and the pet trade.

Stephan says their research can aid conservation efforts in multiple ways, including the creation of jobs for people who might, in other situations, turn to poaching to accrue income.

“Creating alternative income for former hunters by research activities … creates positive attitudes towards conservation and further decreases the support for poaching in local populations,” Stephan said.

Stephan says she and co-author Frederic Gnepa Mehon are working to complete further studies on the putty-nosed monkey vocalizations to broaden their understanding of the “evolution of communicative and cognitive capacities across non-human primate species, and potential parallels to the evolution of human language.”

“There is still far more that remains nebulous about putty-nosed monkey communication and cognition than what we know by now,” she said. “Frederic and I aim to continue contributing insights from forest guenons that might help to unravel the conundrum of animal communication and its relation to our own way to communicate [through] human language.”

Citation: A female putty-nosed monkey Image by C Kolopp / WCS.

Mehon, F. G., & Stephan, C. (2021). Female putty-nosed monkeys (Cercopithecus nictitans) vocally recruit males for predator defence. Royal Society Open Science, 8(3). doi:10.1098/rsos.202135

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