On a remote Panamanian island, researchers have observed for the very first time young male capuchin monkeys stealing howler monkey babies, according to a new study.
Since 2017, researchers have used camera traps to study Panamanian white-faced capuchins (Cebus imitator) on Jicarón Island in Coiba National Park, where the monkeys use stone tools to crack open hard foods like coconuts and crabs.
In January 2022, Zoë Goldsborough, a doctoral researcher at the Max Planck Institute of Animal Behavior in Germany and study lead author, saw footage of a young male capuchin monkey carrying a baby howler monkey (Alouatta palliata coibensis) on its back.
Goldsborough reviewed all the camera footage from around that period and found the same individual, named Joker by researchers, carrying four different howler monkey infants. After no new footage appeared for some time, the researchers decided “it was one individual trying something new,” Brendan Barrett, study co-author and Goldsborough’s adviser, said in a statement. This isn’t uncommon among capuchins, which are “deeply curious animals,” he added.
But after five months, the researchers spotted four more capuchins with howler monkey babies in their camera footage. In all, they observed five capuchins, all young males from the same group, carrying 11 different howler babies for up to nine days. The infants were all less than 4 weeks old.
Initially, the researchers suspected adoption. However, anecdotes of interspecies adoptions mostly involve adult females of one species adopting abandoned babies of another species.
Since only male capuchins were seen carrying howler babies, the researchers speculate the capuchins were stealing them. In some videos, they could hear or see the howler monkey parents calling to their babies from nearby trees.
Male white-faced capuchins are known to care for capuchin babies that aren’t biologically theirs. But in the capuchin-howler dynamic, cameras captured at least four dead howlers on the capuchins’ backs, and the researchers suspect no baby survived, likely because the young males couldn’t provide them with milk.
Why the capuchins take the babies isn’t clear yet, but the authors suggest they might “carry howler infants solely for carrying’s sake” — a behavior one male capuchin likely picked up from another.
Sarah Brosnan, a primatologist at Georgia State University, U.S., who wasn’t involved in the study, told the Smithsonian the male capuchins’ behavior is akin to using a “toy.” “These are juveniles,” Brosnan said. “I don’t think that they are grabbing [howlers] because they’re kidnapping, I think they’re grabbing it because it’s an interesting and engaging toy. It makes noise, it moves.”
The authors write their observations suggest necessity isn’t always the driver of new behaviors, “especially on islands, where both need and free time are often abundant.”
However, if the infant-stealing tradition persists, it could be problematic for Jicarón’s howler monkeys, which are an endangered subspecies, the authors add.
Banner image: A subadult male capuchin with a howler monkey infant. Image courtesy of Brendan Barrett/Max Planck Institute of Animal Behavior.
This story first appeared on Mongabay
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