Why Monkeys are Stealing Babies of Other Species on a Panamanian Island: A Mystery Unraveled by Scientists

At first, behavioral ecologist Zoë Goldsborough saw what she thought was a baby capuchin monkey in her camera trap video. Something felt off, so she showed her colleagues. They were puzzled, too.

Upon closer inspection, they realized it was a baby howler monkey, not a capuchin. Goldsborough was shocked. As she watched more footage, she spotted the same adult capuchin, nicknamed “Joker” because of a scar on his mouth, carrying a baby howler several times. Other male capuchins were doing the same. It left her wondering: why this unusual behavior?

The research team, which included experts from the Max Planck Institute, studied 15 months of footage from Jicarón Island, off the coast of Panama. They discovered that at least 11 howler infants had been abducted by male capuchins. They weren’t eating or caring for the babies, which researchers believe indicates a possible “cultural fad.” This behavior might be a reflection of their unique environment on Jicarón, where howler monkeys are an endangered species.

Goldsborough described the research journey as a roller coaster filled with surprising interpretations that often changed. The team set up camera traps on Jicarón Island, which has no human population. It’s tough to observe these monkeys up close, so they relied on these hidden cameras. However, one limitation is they couldn’t see what was happening in the treetops where howler monkeys live. Thus, confirming how and when capuchins abducted the babies remained elusive.

Initially, the researchers thought it might be an adoption case. Monkeys sometimes adopt abandoned infants, but Joker wasn’t nurturing the howlers. Instead, he carried them around, and sadly, the infants eventually starved.

Pedro Dias, a primatologist, noted this behavior is quite odd for male primates since maternal care is usually observed in females. Similarly, Corinna Most, another behavioral ecologist, initially thought the abductions were for predation. But as the study progressed, it became clear that the capuchins weren’t eating the babies either.

Instead, they carried the baby howlers for days with minimal interactions. Brendan Barrett, one of the study’s co-authors, wondered what drove such energy to take the infants without clear purpose. He pointed out that these capuchins have evolved in an environment without predators. This safety allows them the freedom to explore, which might lead to boredom and other arbitrary behaviors.

Interestingly, boredom can drive innovation, especially among younger animals. Research shows that younger primates often initiate new behaviors. Goldsborough is investigating how the boredom of these capuchins could lead to unique cultural practices, such as stone tool use. Previous studies show younger animals, like the famous "potato-washing" macaque named Imo, often lead in adopting new behaviors.

Overall, it seems that the capuchins might be engaging in a quirky phase. Goldsborough and Barrett hope this behavior fades, much like human trends. They acknowledge that their findings mirror human actions that sometimes harm other species without real purpose. In the end, it highlights how both humans and animals can engage in seemingly senseless activities that impact others.

For more on endangered species, check the IUCN Red List.

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