On the small island of Jicarón, off the coast of Panama, researchers have observed a strange and previously undocumented behavior among male white-faced capuchin monkeys (Cebus capucinus imitator). These monkeys have been seen carrying young howler monkeys (Alouatta palliata coibensis) from nearby Coiba Island, a behavior that has raised questions about the capuchins' motivations and social dynamics. The discovery was made possible by camera traps set up in 2017 after a botanist reported seeing capuchins using stones to feed, which revealed not only tool use but also the unusual act of kidnapping howler monkey infants. The findings were published in the scientific journal Current Biology in July 2025. A video dated January 26, 2022, showed an unidentified young male capuchin carrying a howler monkey infant. The following day, a male named Joker—known for a facial scar—was seen carrying the same young one. This continued for several days until February 3, 2022. Researchers initially thought the howler monkey might have been abandoned and adopted by Joker, but further evidence suggested otherwise. The young howler monkey emitted distress calls typically heard when an infant is separated from its mother, and other howler monkeys responded to these calls, indicating the young had been kidnapped rather than left behind. According to primatologist Zoë Goldsborough from the Max Planck Institute for Ethology and the Smithsonian Tropical Research Institute, the behavior was so unusual that it prompted immediate investigation. The study co-author, Brendan Barrett, noted that while no footage showed how the capuchins captured the howler monkeys, it is known that they can gather in groups to attack the larger howler monkeys. Between April and May 2022, Joker was observed with two other howler monkey young, and videos showed him dragging a third, possibly dead, specimen. Other young male capuchins were also seen carrying howler monkey young, with at least eleven young taken over a fifteen-month period. Researchers believe very few of these young likely survived. The behavior of stealing howler monkey young by white-faced capuchins has not been previously documented, despite an older report of a larger capuchin species in Brazil stealing a howler monkey young. Researchers are intrigued by the social diffusion of this behavior, as it is rare for animals to adopt behaviors without direct physical benefits. Susan Perry, a primatologist from the University of California, Los Angeles, noted that young male capuchins often attempt to capture young of other species, though these efforts usually end in abandonment when the young become too demanding. She suggested that capturing howler monkey young may be particularly unproductive, as these capuchins are more likely to face aggression from their peers. The island environment may play a role in this behavior. On Jicarón, food is abundant and threats are minimal, potentially leading to increased innovation and tool use among capuchins. Zoë Goldsborough explained that animals in predator-free environments, such as islands or zoos, often display more innovative behaviors. While the behavior is considered tragic for the endangered howler monkeys, researchers have chosen not to interfere, hoping the species may adapt by avoiding the capuchin population or the capuchins may eventually lose interest in the activity.