On the isolated island of Jicarón, off the coast of Panama, a troubling phenomenon has captivated primatologists: white-faced capuchin monkeys have adopted a behavior never before observed in wild primates. Since 2022, several young male capuchins have abducted babies of another monkey species—the howlers—for no apparent reason.
At first, it could have been written off as a behavioral anomaly. But what began as a rare incident has evolved into a genuine social trend, to the point of worrying scientists who have been tracking this unique population for years.
A perplexing scene in the jungle
Everything started when a doctoral student, Zoë Goldsborough, studied the Jicarón capuchins through motion-activated cameras. These primates, known for their intelligence and their use of stone tools, were the subject of intensive monitoring. One day, while watching the thousands of videos amassed, she stumbled upon a surprising scene: a young male capuchin carrying a baby howler on its back.
This kind of interspecific interaction had never been documented on the island before. Curious, Goldsborough pulled up the archives and found four similar cases, all involving the same individual, nicknamed “Joker.” At this point, researchers considered it a strange form of adoption.
But very quickly, things began to change.
When a quirk becomes a trend
Five months later, the videos show that other young male capuchins begin to do the same. In 15 months, there are 11 distinct kidnappings of infant howlers. Still very young (less than four weeks old), these infants are seen clinging to the belly or back of their captors, following the group as it moves through the forest.
The most puzzling part? The capuchins do not appear aggressive. “They do not harm them,” Goldsborough notes. But they also cannot feed them. Evidence indicates that none of the abducted babies survived, due to the absence of maternal milk.
A cultural tradition… with no aim
This behavior, as strange as it is tragic, does not seem to confer any clear advantage to the capuchins, nor does it impose any obvious disadvantage. Researchers see it as the emergence of a “social tradition” — a non-human cultural phenomenon transmitted through learning from one individual to another.
“ It’s like a social fashion that spontaneously appeared in one individual, then spread to other young males,” explains researcher Brendan Barrett.
A tradition, yes — but without a clear function. A kind of free innovation born out of boredom?
The luxury of animal idleness?
This is precisely one of the hypotheses put forward by the team. On Jicarón, capuchins live in an exceptionally safe environment: no predators, few rivals, a bountiful forest. This particular context could encourage the exploration of new behaviors, even absurd or non-adaptive ones.
Meg Crofoot, director of the Max Planck Institute of Animal Behavior and co-founder of the project, sums up the situation this way:
“Life is easy on Jicarón. Capuchins have free time and few constraints. Boredom, combined with their social intelligence, could be enough to explain the emergence of this strange tradition.”
A threat to the howler monkeys
But beyond the fascinating aspect of this discovery, the ecological consequences are concerning. The Jicarón howler monkeys are already an endangered species. If this kidnapping trend continues, it could weigh heavily on the renewal of local populations.
The phenomenon thus raises a troubling paradox: a cultural behavior in an intelligent species, but with detrimental consequences for another.
A one-of-a-kind story in the world
To date, no other wild primate population has been observed practicing this type of behavior. For researchers, this underscores the importance of monitoring these behavioral dynamics in real time, especially in a context of global change, where ecological pressures and imbalances can give rise to unexpected behaviors.
“ Being witnesses to the birth and spread of this behavior has been deeply unsettling,” Crofoot concludes. “ It reminds us how capable animals are of imitating, innovating, but also of disturbing their environment.”
