Researchers Spent 600 Hours Watching Chimpanzees Pee

Watch someone yawn and there's a chance you'll yawn, too. Watch someone pee and ... well, if you're a chimpanzee, there's a chance you'll end up urinating as well. So finds a new paper published Monday in Current Biology that NPR reports spun out of a casual observation made by Ena Onishi, a wildlife researcher at Kyoto University. The chimps she was studying "seemed to have a tendency to urinate around the same time," which made her wonder if it was a contagious behavior. What followed was 600 hours spent observing 20 captive chimps, during which Onishi and her fellow researchers tracked each time a chimp urinated, how close they were to other chimps (within arm's reach, within 3 meters, or more than 3 meters away), and whether those other chimps then urinated within 60 seconds.

The upshot after tracking what a press release notes were 1,328 urination events: About 10% of those events appeared to be caught from a chimp within arm's reach, reports NPR, making it a slightly contagious behavior. Proximity had an impact, with the study noting that "individuals spatially closer at the time of urination were more likely to follow the urination of others." And while social closeness didn't have an impact ("they were surprised to find that a chimp that was pals with the first animal to pee wasn't any more likely to follow suit," Scientific American notes), social rank did.

"Individuals with lower dominance status were more likely to follow the urination of others," the study found. Onishi shares potential theories for the behavior: It "could promote a shared readiness for collective behaviors," she tells the New York Times, or reduce their risk of being hunted. "By keeping urination localized, the group can reduce the risk of predators tracking them through the scattered urine scents in their territory," Onishi tells NPR. Andrew Gallup, a behavioral biologist at Johns Hopkins University who wasn't part of the study, tells NPR it might be something simpler: Just hearing or seeing another chimp urinate could trigger the need to pee. (More scientific study stories.)