Capuchin Monkeys Caught on Camera ‘Abducting’ Baby Howler Monkeys in a Strange Tradition Seen for the First Time Scientists on Panama’s Jicarón Island were mystified by photos and videos of young male capuchins carrying howler monkeys on their backs for days at a time Lillian Ali - Staff Contributor May 19, 2025 11:00 a.m. A howler monkey infant, only a few days old, clings to a subadult white-faced capuchin monkey as it uses tools. Brendan Barrett / Max Planck Institute of Animal Behavior In June 2022, while watching footage from an island off the western Pacific coast of Panama, researchers spotted a strange wildlife behavior they’d never seen before. A young, male capuchin monkey walked past the camera with a baby howler monkey clinging to its back. “What am I looking at here?” Meg Crofoot, an ecologist at the Max Planck Institute of Animal Behavior and one of the researchers observing these capuchins, tells Smithsonian magazine about the first time she saw the footage. “It’s so weird.” As they played back more of the recorded videos, the scientists realized they were observing a new social tradition among young male capuchins: abducting baby howler monkeys. The kidnapped howlers were all less than four weeks old, and in some videos taken by the research team, adult howler monkeys can be seen or heard calling out for the missing babies. While the male capuchins did not directly hurt the babies, they could not provide milk to them, and several howlers died of malnourishment, the research team reports in a study published today in the journal Current Biology. Capuchin monkeys are abducting baby howlers. But why? Watch on The research started on Panama’s Jicarón Island in 2017, when scientists obtained enough funding to set up a project there. They placed camera traps, which took photos or videos when they detected motion, and discovered the island’s white-faced capuchin monkeys regularly use stone tools. That marked the first known population of tool-using capuchins. But after several years of monitoring the monkeys, Max Planck Institute of Animal Behavior researcher Zoë Goldsborough observed the new behavior from the group, spotting the first instance of a young male capuchin carrying around a baby howler monkey. “This has never been observed anywhere else, not on this island, or in any other populations of capuchin monkeys,” Goldsborough says in a statement from the Max Planck Institute of Animal Behavior, which, along with the Smithsonian Tropical Research Institute (STRI), funded the research. Because the researchers used motion-sensing cameras, they could easily jump back and forth in time to look for new sightings and retroactively check if they missed old ones. They traced the first instances of this behavior to one monkey, who they nicknamed “Joker,” initially seen carrying a howler infant in January 2022. But at the start, Joker’s antics didn’t seem to catch on. A howler infant carried on the back of Joker, the first capuchin to "innovate" the carrying tradition. A juvenile capuchin looks at them from the side. Brendan Barrett / Max Planck Institute of Animal Behavior Five months after the first sighting, however, researchers saw even more capuchins seemingly copying Joker and carrying howlers. Over 15 months of footage, they observed 11 infant howlers carried by young capuchins, each for up to nine days at a time. While Joker “paid more attention to the babies that he carries,” and was generally more interactive, the capuchins that later adopted the behaviors “really don’t interact with the babies,” says Crofoot, who, along with Goldsborough, is also a research associate at STRI.  Researchers do not know how the capuchins got the howlers in the first place. Howler monkeys primarily live in trees, so Crofoot assumes that is where the capuchins found them. Why capuchins appear to be abducting baby howlers is still unclear, but the team examined multiple possibilities. Since howlers and capuchins have different diets, the researchers ruled out competition for food. They also did not see the “carrier” capuchins getting positive social attention from their peers, though sometimes one capuchin would lose interest in the howler he was carrying and drop it for another capuchin to scoop up. The team’s suggestion? Boredom. Life on Jicarón Island has few competitors and no predators for the capuchin monkeys. This low-stress and potentially under-stimulating environment might lead the monkeys to create new behaviors, the researchers say. “Capuchins appear to carry howler infants solely for carrying’s sake,” they write in the paper. A white-faced capuchin monkey uses stone tools at a streambed while carrying a baby howler on its back. Brendan Barrett / Max Planck Institute of Animal Behavior Susan Perry, a primatologist at the University of California, Los Angeles, who has studied social behaviors among capuchins and was not affiliated with this research, suggests the carrying behavior stems from capuchin males wanting to alloparent other infants, or take care of babies that are not their own offspring. “Male capuchins frequently steal capuchin infants,” Perry writes in an email to Smithsonian magazine. “I think this is because they are trying to develop relationships with infants that are going to be their sidekicks/henchmen when they immigrate.” Georgia State University primatologist Sarah Brosnan, who was also unaffiliated with the research, compares the behavior to the use of a “toy,” especially because it was primarily observed among juvenile and immature capuchins. “These are juveniles,” Brosnan says. “I don’t think that they are grabbing [howlers] because they’re kidnapping, I think they’re grabbing it because it’s an interesting and engaging toy. It makes noise, it moves.” This isn’t the first time a hard-to-explain social tradition has been recorded in capuchin monkeys. More than 20 years ago, Perry observed capuchin groups demonstrating social behaviors, like “hand-sniffing,” when one capuchin sticks a finger up another’s nose for several minutes, and turn-taking “games,” such as when monkeys try to retrieve objects hidden in each other’s mouths. “It suggests that capuchins are really, really interested in these social traditions—really strongly socially motivated—and easily developed these social traditions,” Brosnan adds. To Crofoot, the findings show that humans are not alone in having “arbitrary” social traditions, born from boredom-fueled innovation. Just as humans tend to compare our species to other primates in positive terms, such as with tool use and intelligence, our primate relatives can share hard-to-explain social dynamics that might harm other species as well. “I think that’s a really interesting, important thing for understanding ourselves, even if it also has this kind of grim side to it,” Crofoot says. Get the latest stories in your inbox every weekday.