On the remote island of Jicarón, nestled in Panama’s Coiba National Park, a fascinating and perplexing animal behavior has captured the attention of primatologists and animal behaviorists worldwide. Here, a population of wild white-faced capuchin monkeys has been documented engaging in an unprecedented social tradition: the repeated abduction and carrying of infant howler monkeys, an entirely different primate species. This phenomenon, observed and analyzed over a span of more than a year through an expansive network of motion-triggered camera traps, offers groundbreaking insights into the complexities of animal culture, social learning, and interspecies interactions.
The observations began in early 2022 when Zoë Goldsborough, a doctoral researcher at the Max Planck Institute of Animal Behavior (MPI-AB), noticed an astonishing sight while sifting through thousands of images and hours of footage: a young male capuchin carrying a baby howler monkey on his back. This behavior had never been recorded on Jicarón despite continuous monitoring since 2017, marking a startling deviation from known primate interaction patterns. The initial surprise quickly gave way to curiosity, setting the stage for a detailed investigation into this unusual form of cross-species infant carrying.
The primary carrier was identified as a subadult male capuchin, affectionately named "Joker" by the research team. Over time, Joker was seen carrying not just one but multiple howler infants, sparking questions regarding the origin, motivation, and implications of this behavior. The phenomenon was initially hypothesized to be a form of interspecies adoption, a behavior very rarely documented, typically involving females caring for younger infants as part of a nurturing role. However, the fact that it was exclusively young males engaging in this carrying activity challenged this assumption, hinting at a more complex social dynamic at play.
Following the early spike of observations, the behavior ceased temporarily, leading researchers to speculate whether Joker’s actions were a singular experimental behavior typical of juvenile capuchins’ exploratory nature. Capuchins are renowned for their cognitive curiosity and problem-solving abilities, traits that often lead to novel behavioral innovations within their social groups. The gap in observations also prompted questions regarding the stability and potential spread of this behavior throughout the population.
A breakthrough came when, approximately five months later, new recordings revealed that several other young male capuchins had begun adopting this behavior, carrying howler infants with increasing frequency. This rapidly expanding pattern suggested a form of social transmission, a hallmark of cultural behaviors among animals that are learned not genetically but through observation and imitation. The researchers dubbed this unfolding sequence “a social tradition or cultural fad,” emphasizing the parallels between animal and human culture in the propagation of behaviors that may not necessarily confer obvious benefits to the practitioners.
The interspecies infant carrying typically lasted for periods up to nine days, as documented in extended video sequences. During these times, the capuchins engaged in their daily routines—including extensive tool use to crack open food sources such as nuts and shellfish—while the howler infants clung to their backs or bellies. The astonishing tolerance of prolonged physical contact between species, combined with the lack of aggressive interaction, provides valuable insight into primate social flexibility and raises questions about the cognitive underpinnings of such behaviors.
Yet, this social tradition carries a darker undertone. The howler infants, all less than four weeks old, were effectively abducted from their parents, who were observed vocalizing distress calls from nearby trees. Tragically, at least four of these infants were documented to have died, likely due to deprivation of maternal care and essential nutrition such as milk, which the capuchins cannot provide. The phenomenon thus highlights a rare case where social learning produces behaviors with destructive consequences for a vulnerable species, a situation that opens new discourse on how culture in non-human animals can generate maladaptive outcomes.
This leads to a broader and more philosophical inquiry regarding the drivers of such behaviors. Unlike human cultural evolution, where many traditions evolve to serve some functional benefit, these capuchin behaviors appear to have no clear advantage. The males do not gain increased social standing, mating opportunities, or enhanced access to resources through infant carrying. Nor do they engage in play or other interactions that could suggest a practical purpose. This enigmatic behavioral pattern presents a compelling example of social learning decoupled from immediate fitness benefits.
In addressing why this behavior emerged at all, researchers point toward environmental and ecological factors unique to Jicarón Island. The absence of predators and a scarcity of competitors may have created an environment of low external pressures, effectively producing a form of ecological luxury. Under such conditions, boredom and excess free time among intelligent and inquisitive capuchins could act as the impetus for innovation and experimentation. Such an interpretation challenges the classical notion that necessity is the mother of invention, offering instead that cognitive play and social experimentation are important drivers of cultural evolution in animals.
Moreover, the fact that only male capuchins both carry howler infants and participate in the island’s established tool use behaviors suggests a potential connection between these social traditions. Both could stem from the same underlying cognitive and social state—perhaps a form of restlessness or boredom in a relatively stress-free environment, leading to the birth of novel and unexpected behaviors that ripple through the social fabric of the group.
The social dynamics observed underscore the intricate ways in which culture can evolve in animal societies, revealing a capacity for innovation, transmission, and even the adoption of behaviors that might, paradoxically, harm other species. This discovery challenges rigid frameworks that equate animal culture strictly with adaptive benefits and underscores the richness and variety of social learning mechanisms across taxa.
Looking forward, ongoing analysis of the extensive camera trap data, accumulated between January 2022 and July 2023, will shed light on the persistence and potential ecological ramifications of this behavior. If the infant-carrying tradition continues to spread to other capuchin groups or increasingly impacts the endangered howler monkey population on Jicarón, the phenomenon could evolve into a critical conservation concern, necessitating management interventions within Coiba National Park.
Witnessing such a bizarre and unprecedented social phenomenon has profoundly impacted the researchers involved. As Meg Crofoot, managing director at MPI-AB, eloquently puts it, this natural population of capuchins provides a unique live model for understanding animal culture’s surprising and sometimes unsettling trajectories. The team feels a deepened responsibility to continue monitoring, studying, and learning from these intelligent monkeys who have, unintentionally or not, crafted a social tradition bridging species boundaries in a way unseen before.
The findings were recently published in the journal Current Biology, marking a seminal contribution to the study of animal behavior, culture, and interspecies relationships. As we unravel more about the cognitive and social complexities of capuchins on Jicarón, this story reminds us that the natural world still harbors enigmas as strange and fascinating as those in human societies, warranting our ongoing curiosity and respect.
Subject of Research: Animals
Article Title: Rise and spread of a social tradition of interspecies abduction
News Publication Date: 19-May-2025
Web References: Max Planck Institute Interactive Website
References: Current Biology, DOI: 10.1016/j.cub.2025.03.056
Image Credits: Brendan Barrett / Max Planck Institute of Animal Behavior
Keywords: Capuchin monkey, howler monkey, social tradition, animal culture, interspecies behavior, primate tool use, social learning, behavioral ecology, infant carrying, cultural transmission
