Researchers on a remote island off Panama have documented something truly bizarre: young male capuchin monkeys are abducting infant howler monkeys, carrying them around for days—and sometimes, it ends in tragedy.
This never-before-seen behavior was caught by motion-triggered camera traps set up in the forests of Jicarón Island, which is just off the coast of Panama. Scientists from the Max Planck Institute of Animal Behavior have been studying the tool use of Panamanian white-faced capuchins since 2017, but in 2022, their cameras captured something no one expected.
It all started with one monkey.
The Joker Starts a Trend
In January 2022, a juvenile male capuchin, nicknamed “Joker” for a scar near his mouth, was seen carrying a live infant howler monkey on his back. Over the next few months, Joker was spotted with four different howler infants—sometimes holding onto them for up to nine days. Then, other young males started doing the same, because the capuchin is so social all you need is one monkey to start the odd behavior and others will follow behind them.
By late 2022, at least four more capuchins were recorded carrying howler infants. In total, the researchers documented 11 separate “abductions,” all led by young male capuchins.
“It is a very capuchin thing to do. They’re very curious. They like to poke and bother all other creatures,” said Susan Perry, an evolutionary anthropologist at the University of California, Los Angeles. “I would guess that they don’t mean any harm to these babies, but they don’t get that the howlers need milk.”
Not Just Monkeying Around
Capuchins are known for being clever and social, often seen cracking open fruit and shellfish with stones. But this behavior stunned even seasoned primate experts.
Some of the capuchins appeared to treat the infants gently—cradling or grooming them—but others showed frustration, especially when the howlers tried to nurse. If the babies cried or reached for milk, the capuchins sometimes bit or pushed them away.
Tragically, at least four of the infant howlers died, likely from malnourishment. Others disappeared without a trace. In some cases, capuchins continued carrying the lifeless infants even after death.
Why Are They Doing This?
The big question: what’s the reason behind this strange behavior?
Theories range from social bonding to simple boredom. Capuchins on Jicarón Island face no predators and few competitors. With plenty of free time, some researchers believe these highly intelligent monkeys may be inventing their own “games”—and in this case, it’s a dangerous one.
“We did sometimes see them being affectionate or affiliative towards the howler monkey infants,” said Brendan Barrett, co-author of the study. “It’s almost like a kid having a jar of lightning bugs. They think it’s cool. But from the lightning bugs perspective, it’s not the best situation.”
Researchers believe that being there is no social benefit to kidnapping and carrying these babies around that the capuchins are doing it simply because they are bored and they can. Howler monkeys are larger than capuchins, however capuchin monkeys are much faster.
A Rare Look at Primate Minds
While heartbreaking, the study provides new insight into the social lives of capuchins—and a reminder of how complex and unpredictable animal behavior can be.
Researchers hope the findings will deepen our understanding of social innovation in wild primates. For now, though, they’re still trying to answer the question that sparked it all: what was Joker thinking?