On a remote island in Panama’s Coiba National Park, researchers have recorded white-faced capuchin monkeys engaging in an unusual form of social behavior that has not previously been documented in any primate species. Over a 15-month period, five immature male capuchins were observed carrying infant howler monkeys for multiple days at a time.
A study published in the May 2025 issue of Current Biology describes the behavior as a “non-adaptive cultural tradition.” According to the authors, the capuchins repeatedly abducted and transported at least eleven individual howler monkey infants between January 2022 and March 2023. The scientists concluded that the behavior provided no clear benefit to the carriers and was not motivated by food acquisition, parental care, or play.
“This is the first known documentation of a cultural tradition in which animals repeatedly abduct and carry infants of another species—without any clear benefit to themselves,” said lead author Zoë Goldsborough, a researcher with the Max Planck Institute of Animal Behavior.
Capuchins are a genus of New World monkeys known for their cognitive flexibility, complex social lives, and frequent use of tools. They are part of the Cebinae subfamily, whose members have demonstrated some of the most sophisticated learned behaviors observed among non-human primates. In the wild, capuchins have been recorded using sticks to extract insects from cavities, smashing fruits and snails against hard surfaces, and even fashioning probing tools for termite fishing.
Social learning is central to capuchin societies. Young individuals often acquire behaviors by watching others, and juveniles have been documented imitating older group members in tasks such as food processing and grooming rituals. Tool use, play-fighting, cooperative alliances, and certain vocalizations are among the behaviors known to be passed down through observation rather than instinct.
The capuchin group studied on Jicarón Island has previously been identified for its habitual use of stone tools to crack nuts and shell Terminalia seeds. To monitor the group’s behavior over time, researchers deployed 86 motion-triggered cameras across the monkeys’ home range. These cameras captured 131 separate instances in which capuchins were seen carrying howler infants. These infants, according to the study, were estimated to be between one and four weeks old.
The researchers traced the behavior’s origin to January 2022, when a juvenile male nicknamed “Joker” was first recorded carrying a howler infant. He later carried three additional howler monkeys. By September 2022, the behavior had spread to four other immature males. The carriers transported the infants on their backs and stomachs during normal activities such as foraging and resting. Some infants were carried for as long as nine consecutive days.
“Most howler infants appeared healthy in initial sightings, but deteriorated over time. At least four howler infants died, seemingly from malnourishment,” the authors wrote. There was no evidence of wounding, consumption, or predation. In one recorded encounter, several capuchins prevented an adult howler from recovering her infant by posturing and issuing threat displays.
The press release issued by the Max Planck Institute emphasized that “the males don’t eat the infants, they don’t play with them, and they don’t receive more attention from their group mates while carrying an infant.” The study’s authors found no indication that the behavior conferred status or reproductive advantages on the carriers. “Capuchins appear to carry howler infants solely for carrying’s sake,” the paper states.
Later adopters of the behavior were recorded engaging in actions that increased risk to the infants, including opening nuts with stones while carrying them. In one case, a howler infant fell from the carrier’s back during such activity. The authors describe the behavior as a potential “fashion trend,” referencing earlier findings from chimpanzee groups in which individuals placed grass in their ears despite the absence of any clear function.
While reports of cross-species caregiving exist in the animal kingdom, they are rare and often limited to isolated cases. Domestic dogs have been known to nurse kittens or piglets. Some dolphins have been seen assisting injured members of other cetacean species. However, systematic and socially transmitted interspecies caregiving behaviors are not well documented outside of primates. In particular, repeated, non-functional interspecies infant carrying, such as that reported by the Jicarón study, has not been previously confirmed in any non-primate animal population under natural conditions.
The howler monkeys involved in the study belong to the subspecies Alouatta palliata coibensis, which is endemic to Coiba National Park and classified as endangered. The authors note the potential implications of this behavior for conservation. “If this tradition of infant abduction persists, it poses a serious conservation risk,” the paper concludes.
The findings expand the scope of research into primate behavioral traditions. They also raise questions about the emergence of behaviors that spread through imitation without yielding clear evolutionary advantages. As Goldsborough and her colleagues suggest, under certain ecological conditions, including low predator pressure and minimal social disruption, primate societies may create cultural behaviors that are not directly tied to survival or reproduction.
The behavior recorded on Jicarón Island illustrates how social learning can produce unexpected outcomes in the animal world. It also reinforces the importance of long-term behavioral monitoring in understanding the dynamics of wildlife populations and the cultural traits that may influence their future.
Goldsborough, Zoë, et al. “Rise and Spread of a Social Tradition of Interspecies Abduction.” Current Biology, vol. 35, no. 10, 2025, pp. R375–R376.
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