Capuchins have started abducting newborn howler monkeys in bizarre, deadly fad

[Bayard]

Young male capuchins have developed a strange trend of acquiring baby howler monkeys. It doesn't end well for the babies.

Wild capuchin monkeys have been kidnapping infant howler monkeys, putting them on their backs and taking them for a ride. The trend, which began with one male, spread to other members of the group, and has resulted in deaths of at least four infants since 2022. "The sort of rate at which we see the infants appearing suggests they are not just finding these infants, they are getting them," study co-author Zoë Goldsborough, a behavioral ecologist also at Max Planck Institute of Animal Behavior in Konstanz, Germany, told Live Science. The unprecedented behaviour was spotted by camera traps set up on Jicarón Island off the coast of Panama. Panamanian white-faced capuchins (Cebus imitator) are social monkeys, living in groups in the forests of Central America. The monkeys are smart and learn fast, and were being monitored by motion-triggered cameras to study tool use.

The team from the Max Planck Institute started putting the camera traps on the ground on Jicarón Island in 2017. "These monkeys don't have terrestrial predators, so these capuchins spend the overwhelming majority of their time on the ground," co-author Brendan Barrett, an evolutionary behavioral ecologist at the Max Planck Institute of Animal Behavior, told Live Science. The cameras revealed the capuchins using stones like hammers to crack open snails, fruit called sea almonds and hermit crabs. But Goldsborough, Barrett and their colleagues also saw something even more surprising. The first glimpse of the odd behavior was in January 2022, when one juvenile male capuchin — whom the researchers named Joker after the "Batman" character because of a scar near his mouth — was seen carrying an infant howler monkey on his back. In the months that followed, Joker was spotted carrying four different howler infants for periods of as long as nine days.

And the behavior soon caught on. From September of the same year, four other young male capuchins were caught by the cameras carrying infant howler monkeys for days at a time. A total of 11 infant howler riders were spotted in all, the researchers report in a study published Monday (May 19) in the journal Current Biology. How the capuchins got hold of the infants is unknown, because it happened away from the cameras, but the researchers think the capuchins are abducting them from adult howler monkeys (Alouatta palliata coibensis). "It very likely happens in the trees," Goldsborough said. "I think the term abduction is realistic and adequate for this," Katherine MacKinnon, a biological anthropologist at Saint Louis University in Missouri, who wasn’t involved in the research, told Live Science.

MacKinnon said the howler monkeys are much bigger than capuchins, but they're slower. "I've watched them grapple with capuchins and it's like watching the howlers in slow motion and the capuchins on 45 record speeds. Howlers can put up a fight, but capuchins are in another class." The abducted howler infants seemed healthy at first, but were very young, so needed milk from their mothers to survive. Their health worsened in the days following their abductions and at least four of them died, probably from malnourishment. "We have confirmed deaths of four and for the others it's unknown. Some of them, the youngest ones, are one or two days old, so it's unlikely that a lot of them survived," Barrett told Live Science. Three infants were carried for at least a day after dying. In two sightings, the carrying male capuchins embraced their infant riders, but generally, they just carried them neutrally. However, the capuchins did seem to get annoyed if the young howlers did something they didn't like, such as attempting to suckle, and would bite or push them away.


An infant howler monkey clinging to the back of a young male capuchin. Researchers discovered the strange trend of howler abduction after placing camera traps to study tool use. (Image credit: Brendan Barrett / Max Planck Institute of Animal Behavior)

https://www.livescience.com/animals/monkeys/capuchins-have-started-abducting-newborn-howler-monkeys-in-bizarre-deadly-fad