Monkey sees, monkey does: Capuchin monkey begins to escape the weird trend of kidnapping baby ll

On an island off the coast of Panama, scientists documented new behaviors of white-headed monkeys, which began with a curious person and spread in a cultural phenomenon about it. The researchers used a motion-triggered camera to capture young male capuchin monkeys, kidnapping the little and mouse monkey for a few days at a time – without obvious benefits for themselves, but with fatal consequences for the baby.

This discovery, published on May 19 in Current Biology, provides a rare glimpse into the origin and spread of the cultural traditions of wildlife. Researchers at the Max Planck Institute of Animal Behavior (MPI-AB) documented 11 different infants howller monkeys carried five immature male tail rolls on the island of Jicarón in the Panama Gobaba National Park.

What makes this discovery particularly important is that researchers witnessed the exact moment of the birth of social traditions, which are rarely documented in wildlife populations. As the behavior spreads from one innovative monkey to the rest of his team, the camera captures not only the first event, but the entire progress.

The birth of a strange tradition

This unusual behavior first appeared in January 2022, when PhD researcher Zoë Goldsborough discovered something strange in camera lenses.

“It was so weird, I went straight to the consultant’s office and asked him what it was,” Goldsborough recalled.

After combing through thousands of images and videos, Goldsborough discovered that a specific male capuchin monkey (she named “The Joker”) lasted four different how babies for up to nine days. Then, five months later, the behavior surfaced – a period of time performed by four additional young male tail roll animals.

The video shows that over 15 months, the five capsules had 11 different hows called babies. As capuchin monkeys engage in normal activities, including using stone tools to crack open food, it is observed that babies, less than four weeks old, are clinging to the carrier’s back or abdomen.

Not adoption, but kidnapping

Although the researchers initially considered whether this might be a case of interspecies adoption, several factors point to a darker reality:

• Roaring babies appear at unusually high (sometimes simultaneously)
• Adult ll was captured on camera with missing baby
• The tail can actively prevent babies from escaping attempts
• In one case, other curly tails threaten an adult’s llo call, trying to retrieve the baby
• At least four infants died, possibly due to malnutrition

Goldsborough stressed: “Capuchins don’t hurt babies, but they can’t provide the milk that babies need to survive.”

What makes this behavior particularly confusing is the apparent lack of benefits for capsules. They don’t eat babies, don’t play with them, and won’t get more attention when carrying their companions.

“We don’t see the obvious benefits of capuchin monkeys, but we don’t see any clear costs, even though this may make the tool more tricky,” Goldsborough said.

Why does this behavior spread?

The researchers believe that the initial carrier’s behavior did not invade his captives and could represent misleading congenital care, which is a false instinct to care for the baby. But later adopters sometimes acted positively on the babies they carried, and they seemed to be involved in something similar to fashion trends.

Will these highly intelligent primates be boring? The team believes this may be a key factor.

Meg Crofoot, managing director of MPI-AB, explained: “It looks easy on Jicarón. There are few predators and competitors, which brings a lot of time to the tail rolls, with little to do. It seems like this ‘luxury’ life is a scenario for these social animals to become innovators.”

She added: “This new tradition shows that necessity does not have to be the mother of invention. For a monkey who lives in a safe, and may not be enough, boredom and free time may be enough.”

Animal culture with destructive results

This study provides an unprecedented window for how animal cultural traditions emerge and spread, even if they do not have obvious adaptive purposes. It also raises important questions about the darker side of animal culture.

“We show that non-human animals are also capable of developing cultural traditions without clear functions, but can bring destructive results to the world around them,” said Brendan Barrett, group leader for MPI-AB and Goldsborough consultants.

Barrett believes that the more interesting question is not why this tradition appears, but why it appears in this particular position. Jicarón Island is home to the only known masonry tool capsule population in the genus Cebus, another cultural innovation unique to that population.

Interestingly, the use of tools and the behavior of infants is mainly performed by young men, suggesting that there may be a link between these two sociological traditions.

The camera surveillance period ended in July 2023, and researchers do not yet know whether this behavior continues or spreads further. If it continues to affect the endangered ridge lutworm on the island, it may become a concern for conservation.

“Witnessing the spread of this behavior has had a profound impact on all of us,” Croft said. “We therefore feel more responsible for continuing to learn from this natural primate, who, to the best of our knowledge, are the only people on Earth who practice this strange tradition.”

As for the actual kidnapping mechanism – the little capuchin can take nearly three times the size of a baby from an adult ll’s baby – this mystery remains. Cameras located on the ground will not capture the tree activity that may occur in kidnapping. However, this study creates an unprecedented record of the origins and dissemination of cultural fashion, providing valuable insights into the complex social dynamics of our primate relatives.

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