These capuchins are abducting babies from howler monkeys—for fun?

While there had been at least one earlier report of a capuchin from a larger species in Brazil stealing a howler monkey infant and carrying it off in its mouth, presumably to eat it, this study is the first to document white-faced capuchins abducting infants in this way—and researchers are especially fascinated that the behavior was subsequently picked up by other individuals, too.

“This observation is particularly intriguing because examples of the social spread of such behaviors with no apparent fitness benefits in animals other than humans are rare,” says Izar. Because there had been camera traps on the island for years before this behavior was ever observed, the researchers probably captured the first time it happened, or at least a very early occurrence.

It is not unusual for young capuchin males to be seen carrying infants of their own species, says Susan Perry of the University of California, Los Angeles, who has studied Costa Rican capuchins at another site for decades, but was not involved in the current study. “Capuchin males often try to steal capuchin infants, and they seem extremely pleased—as if they’ve won a prize—when they succeed. Until the infant gets hungry and starts crying for milk.”

At that point, the infants tend to be abandoned. “Fortunately, the infant’s mother or other female relatives are usually lurking nearby to retrieve their infants.” Capuchin males have a preference for male infants, says Perry. “We think the infants they develop a close relationship with early on will often grow up to become allies with whom they can make the risky move to another group to mate.”

Abducting howler monkeys would obviously be useless in this regard, but perhaps their urge to carry infants is so strong that it sometimes misfires, says Perry. Goldsborough and Barrett agree, but they believe another tendency may be misfiring as well—the desire to do as others do. Perhaps Joker really just wanted to carry an infant, and then the others just wanted to have a go at it as well.