Young male capuchins on an island in Panama have kidnapped 11 infant howler monkeys over the past 15 months, holding them captive for hours or days before releasing them. This is the first documented case of cross-species kidnapping in primates, and it appears to be spreading.
You'd expect primates to mostly ignore other species. Different monkeys occupy different ecological niches, eat different foods, and rarely interact beyond the occasional territorial scuffle. When they do interact, it's usually predatory or competitive. What you would not expect is for one species to start systematically abducting the babies of another, apparently just for fun. Yet that's exactly what's happening on Barro Colorado Island, where capuchins have turned infant-snatching into what researchers describe as a spreading behavioral tradition—less like an evolved survival strategy and more like a cruel fad that juveniles are teaching each other.
According to research published in Current Biology, the kidnappings began in early 2023 when a young male capuchin first grabbed a baby howler monkey. The behavior was so unusual that researchers initially doubted it would persist. Instead, it spread. By mid-2024, at least four other juvenile male capuchins were participating. The abductions follow a consistent pattern: a capuchin grabs an infant howler, carries it away from its mother, and holds it for anywhere from a few minutes to several days. The captive monkeys are sometimes treated roughly—researchers documented cases of infants being dangled, dragged, or struck—though they're eventually released, usually unharmed. None of the howler infants have been killed or eaten. This isn't predation. It's something weirder.
What makes this behavior truly anomalous is that it serves no obvious purpose. The capuchins aren't acquiring food, territory, or mates. They're not reducing competition or improving their social standing in any measurable way. According to the research team's analysis, the kidnappings appear to be what primatologists call play behavior or display behavior—actions that look like practice for dominance or social competence but don't translate into actual survival advantages. The fact that multiple individuals independently started engaging in it, and that it persists despite offering no fitness benefit, suggests something remarkable: capuchins might be engaging in culturally transmitted behavior that's arbitrary and possibly pointless, much like human fads.
Why this started is still mysterious. One hypothesis is that juvenile male capuchins use such dramatic actions to practice dominance displays or to impress peers—a kind of risky one-upmanship among young males trying to establish themselves socially. Another possibility is that it's simply novel play behavior that one individual invented and others copied because it was interesting or challenging. Primatologists have documented cultural transmission before—different populations of chimpanzees use different tools, for instance—but this is the first time researchers have watched a seemingly arbitrary, pointless behavior spontaneously arise and spread across individuals in real time.
The howler monkeys on Barro Colorado Island appear stressed but resilient. Mothers retrieve their infants promptly once capuchins lose interest. No long-term harm has been documented. What's genuinely unsettling—or fascinating, depending on your perspective—is that this reveals something about primate cognition that we're only beginning to understand. Capuchins apparently have the capacity not just to copy behaviors, but to spread behaviors that serve no adaptive purpose, purely because other members of their group are doing it. That's culture in its most arbitrary form. It's also a reminder that evolution doesn't just produce efficient, purposeful creatures. Sometimes it produces creatures clever enough to invent pointless trends, and dumb enough to follow them.