A Social Tradition of Interspecies Abduction

演化之聲
Mar 13
2 min read

Updated: Apr 10

Photos showing interactions between a white-faced capuchin (Cebus capucinus imitator) and infant Coiba Island howler monkeys (Alouatta palliata coibensis)（Image source：Goldsborough Z et al， CC BY 4.0 ） — Photos showing interactions between a white-faced capuchin (*Cebus capucinus imitator*) and infant Coiba Island howler monkeys (*Alouatta palliata coibensis*)（Image source：Goldsborough Z et al， CC BY 4.0 ）

"Kidnapping" behavior is extremely rare in the animal kingdom. Yet on Jicarón Island in Coiba National Park, Panama, an unusual tradition has emerged. A population of Panamanian white-faced capuchin monkeys (Cebus capucinus imitator) has repeatedly abducted infants of the Coiba Island howler monkey (Alouatta palliata coibensis). All documented incidents occurred within a single capuchin group on the island. This same group is also known for another unusual behavior: using stones to crack open the fruits of the tropical almond tree (Terminalia catappa) to access the edible interior, a practice that is itself highly distinctive among capuchins.

Observers traced the earliest occurrence of this interspecies abduction to January 26, 2022. The initial individual responsible was a subadult male white-faced capuchin, referred to by researchers as Joker. He was first recorded carrying a newborn howler monkey infant on his back. Over time, this behavior began to spread within the group. By March 2023, four additional subadult or juvenile male capuchins had begun participating. Together they abducted at least eleven howler monkey infants, carrying them for periods ranging from two to nine days.

（Image source：Goldsborough Z et al， CC BY 4.0 ）

At the time of first observation, most of the abducted howler infants appeared healthy. As time passed, however, they gradually weakened and showed signs of malnutrition, and some eventually died. Why young male capuchins engage in such behavior remains uncertain. Researchers suggest that these males, being in a developmental stage characterized by heightened curiosity and experimentation, may be particularly prone to innovation and social imitation. Carrying a howler infant might also function as a potential social signal within the group, or possibly serve as a buffering element in social tension.

Among the individuals involved, only Joker displayed behaviors resembling parental care toward the infants. Later imitators behaved quite differently. Some showed clear neglect or even aggression. For instance, several capuchins continued to use stone tools while carrying howler infants, occasionally causing the infants to fall. Because of these patterns, researchers propose that the behavior resembles certain socially transmitted "fashion-like" traditions observed in other primates. A well-known example is the "grass-in-ear" custom once recorded in chimpanzee communities. Such traditions appear to spread through imitation despite lacking any clear practical function or adaptive advantage.

The ecological conditions of Jicarón Island may help explain why such behaviors arise. The island environment supports relatively low species diversity and reduced predation pressure. Under these circumstances, animals may experience fewer survival constraints and weaker social pressures, resulting in greater behavioral flexibility. The availability of free time, combined with reduced environmental stimulation, could even produce a form of behavioral boredom. In such settings, novel behaviors may emerge simply because animals have the opportunity to experiment.

From this perspective, innovation does not always arise from necessity. While ecological demands can certainly promote new behavioral strategies, idle time and behavioral freedom can also provide fertile ground for unusual traditions to develop.