Why Are These Capuchin Monkeys Kidnapping Howler Monkey Babies?

On a remote, human-free island off the coast of Panama, something strange is going on: capuchin monkeys are kidnapping baby howler monkeys. And they’re not eating them, hurting them, or raising them. They’re just…carrying them around.

“This was very much a shocking finding,” said Zoë Goldsborough, a behavioral ecologist at the Max Planck Institute of Animal Behavior. “We’ve not seen anything like this in the animal kingdom.” The research, published this week in Current Biology, documents 11 separate incidents between 2022 and 2023 where white-faced capuchins were seen toting infant howlers on their backs—despite not being the same species.

Scientists had originally set up 80+ camera traps on Panama’s Jicarón Island to study the monkeys’ tool use. But instead of just catching footage of stone-cracking capuchins, the cameras captured them walking, climbing, and hammering away—with baby howlers clinging to their fur. One monkey, nicknamed Joker, was the first repeat offender. But after a while, four other males joined in.

Why Are These Capuchin Monkeys Kidnapping Howler Babies?

“We’ve all spent hours wracking our brains why they would do this,” said Goldsborough. Theories ranged from misdirected caregiving to something even stranger: a social fad. The abductions appear nonviolent, and in some cases, the monkeys continued to carry the infants even after they had died—likely from starvation. “A hopeful part of me wants to believe some escaped and went back to their mothers, but we don’t know,” said co-author Margaret Crofoot.

Goldsborough believes the behavior may have taken hold as part of the group’s evolving “culture”—a rare phenomenon in non-human animals, but not unheard of. It’s like the orcas wearing dead salmon like hats, or chimps sticking grass in their ears for no apparent reason. “To me, it appears less as if they want to keep the howler infant because they are so interested in them…but more that they carry them as an ‘accessory,’” she told ScienceAlert.

So why here, and why now? The capuchins of Jicarón live unusually cushy lives—no predators, no major threats, and plenty of free time. That combination of safety and boredom might be the perfect breeding ground for weird behavior.

To watch the rise and spread of this eerie trend in real time, the Max Planck Institute has published a detailed interactive timeline of the monkey kidnappings.

Humans often search for reflections of ourselves in the animal world—empathy, intelligence, tool use. But sometimes, the mirror shows us something a little harder to explain.