Unusual behavior was observed between 2022 and 2023 on a small island in Panama, where capuchin monkeys were recorded carrying baby howler monkeys. This discovery was made by researchers from the Max Planck Institute of Animal Behavior and the Smithsonian Tropical Research Institute while analyzing footage from more than 80 cameras originally installed to study tool use among capuchins. The video showed at least 11 howler infants being transported on the backs of male capuchins. These two monkey species are not closely related. Most of the baby howlers were only a few weeks to months old and still dependent on their mothers. The reason behind this behavior remains unclear, but it has never been documented before. The findings were published in the scientific journal Current Biology.

Experts have suggested that the first case might have come from a confused caring instinct, as the male capuchin appeared gentle while handling the infant. Other young males later imitated this conduct. There were no signs of hostility or feeding behavior, which excluded the possibility of predation. Sadly, most of the infants were believed to have died from starvation, and some were seen being carried even after death. Scientists noted that similar behavior—carrying dead young—has been observed in other animals, such as gorillas and whales, but the reasons are still speculative. This phenomenon has shown the exceptional behavioral diversity within primate social groups and emphasized the importance of further investigation into animal cognition and social learning. Only one group of capuchins has shown this specific conduct so far.