Scientists Puzzled by Capuchin Monkeys Kidnapping Baby Howlers

Researchers studying primate behavior on a remote Panamanian island have discovered an unprecedented and disturbing phenomenon: young capuchin monkeys are systematically kidnapping baby howler monkeys from rival species, apparently for entertainment. The bizarre behavior, captured on camera traps over 15 months, has left scientists scrambling to understand what drives these cross-species abductions that often prove fatal for the infant victims.

Scientists at the Max Planck Institute of Animal Behavior documented at least 11 infant howler monkeys being carried by capuchins on Jicarón Island between January 2022 and March 2023, representing the first recorded instance of such behavior in the animal kingdom, according to NPR.

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The Birth of a Disturbing Trend

The unusual behavior began with a young male capuchin nicknamed “Joker” due to a distinctive facial scar. Camera footage shows Joker first carrying a howler infant in January 2022, initially treating the baby with some semblance of care. However, by September 2022, four additional young male capuchins had adopted the practice, carrying kidnapped infants more like “accessories” than living creatures.

Behavioral ecologist Zoë Goldsborough initially thought she was observing capuchin babies when reviewing camera trap footage designed to study tool use. A closer examination revealed the disturbing truth: the small figures clinging to capuchin backs belonged to an entirely different, endangered species.

Fatal Consequences for Victims

The kidnapping behavior proves consistently deadly for howler monkey infants, who range from days to months old and are still dependent on maternal nursing. Unlike the documented case of a female capuchin in Brazil successfully raising a marmoset infant, these male capuchins lack the ability to provide proper care.

Camera footage captured tragic evidence of starvation among the kidnapped babies, with some capuchins continuing to carry corpses like “puppets or dolls.” Adult howler monkeys were recorded making distress calls, attempting to locate their missing offspring, while the infants themselves made “lost” calls indicating they were not abandoned but actively abducted, according to Associated Press.

Cultural Fad Theory

Researchers believe the kidnapping represents a “cultural fad” among the island’s capuchin population, similar to other documented primate trends like killer whales wearing salmon hats or capuchins in Costa Rica temporarily grooming porcupines. The behavior appears to spread through social learning rather than serving any evolutionary purpose.

The capuchins on Jicarón Island enjoy unusual conditions that may contribute to innovative behaviors. With no natural predators and abundant food sources, the monkeys have excess time and energy that may lead to experimentation with novel activities. This same environment previously enabled the development of stone tool use, making these capuchins the only known population to employ such technology.

Island Laboratory Conditions

Jicarón Island, located 55 kilometers off Panama’s coast within Coiba National Park, serves as an ideal natural laboratory for studying primate behavior. The island’s isolation and predator-free environment have allowed researchers to observe behaviors that might not emerge under normal ecological pressures.

Brendan Barrett, an evolutionary behavioral ecologist involved in the study, describes capuchins as “chaos agents” that naturally manipulate their environment. “They’re highly innovative, they’re highly explorative. They do interesting, strange things,” he explained, according to CNN.

Implications for Endangered Species

The kidnapping behavior poses additional threats to the island’s howler monkey population, which represents an endangered subspecies of mantled howler monkeys. Female howlers typically give birth only once every two years, making each infant particularly valuable for species survival.

Researchers are now investigating whether the howler population will adapt defensive strategies to protect their young, such as maintaining greater distance from capuchin territories. The behavioral flexibility required for such adaptation could determine the long-term survival prospects for the endangered howler population.

Research Methodology and Future Study

The discovery emerged from an extensive camera trap network established in 2017 to study capuchin tool use after a botanist reported seeing the monkeys using stones to process food. Over 80 cameras documented the kidnapping behavior across 19 months of footage, providing unprecedented insights into the development and spread of primate cultural practices.

Scientists plan to continue monitoring both species to understand whether the kidnapping behavior will evolve, fade away, or inspire additional unusual cultural innovations. The research demonstrates how isolated environments can serve as incubators for behaviors that challenge our understanding of animal cognition and social learning. The study was published in the journal Current Biology, highlighting the significance of this unprecedented primate behavior for understanding animal culture and innovation.

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