The “striking” gesture has been observed for at least ten years among the zoo mandrill—the world’s largest monkey, according to a new study.
The 23 mandrills in the group all cover their eyes, regardless of age or sex, sometimes for more than 30 minutes and while also raising their elbows in the air.
Laidre and colleagues believe the gesture arose from an individual and was copied by other mandrills, and eventually developed its own meaning.
Scientists aren’t sure exactly what it means, but the rough translation might be “leave me alone.”
operates.”Because the gesture emerged naturally, independent of human involvement, and has now lasted a full generation, it could be considered a cultural behavior, the authors say.
Mark Laidre, an integrative biologist at the University of California, Berkeley, studied 19 other mandrill communities in North America, Europe, and Africa—the monkey’s native continent—and found no other evidence of eye-covering.
The mandrills will cover their eyes for more than 30 minutes.
Laidre told me by email that he also queried several long-term primate observers, and none have seen the behavior.
“While I imagine that other primate species might occasionally cover their eyes, the behavior does appear fairly unique,” he said.
“And at least in mandrills, very few of the hundreds of individuals I have observed around the world do this behavior. So it is obviously special in mandrills, and may not be very common in other species either.”
Monkey-gesturing study published February 2 in the journal PLoS ONE.
Photos courtesy Mark Laidre, University of California, Berkeley