One of the biggest problems in studying animal communication is figuring out whether the animals know what they are doing. A bird may screech and another bird may understand that the screech is a response to danger. But that doesn’t prove the screecher intended to warn others. It might have been a predictable but involuntary response to something scary, like a scream at a horror movie.
So scientists spend a lot of time testing animals in ingenious ways to figure out what might be going on. Three scientists testing wild chimpanzees in Uganda reported Wednesday in the journal Science Advances that chimpanzees can do something that previously had only been known in human beings. They change the way they are communicating to take into account what their audience knows.
Humans do this all the time. To a fellow baseball fan you might say, “So, there’s a runner on third, one out, bottom of the ninth, and McAfee hits a sac fly.” To someone from another planet, you might say, “There was a really exciting moment in a sporting event I was attending last night.” Or you might just forget it.
Catherine Crockford and Roman M. Wittig of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and Klaus Zuberbühler of the University of St. Andrews in Scotland were studying wild chimpanzees in Uganda, so the subject of their communication was snakes, not baseball. When a chimp saw a realistic model of a snake, the animal would make more sounds — called hoos — and make a greater effort to show where the snake was if it seemed that other chimps in the area were unaware of the danger. If it seemed other chimps already knew about the snake, it would make fewer calls and stay a shorter time at the danger.
To run the experiment, the researchers put a model snake on a path chimpanzees used. When a chimp came along, before it reached the snake, they would play two different chimp calls — either a “rest hoo” or several “alert hoos.” The rest hoo would be made by a chimp that was resting, not aware of any danger. The alert hoos would indicate the chimp who made it had seen something dangerous, like a snake. So the chimp on the trail would know either that its neighbors were clueless or aware of danger.
Shortly after the researchers played the calls, the chimp on the trail would encounter the realistic model of a snake. After hearing alert hoos, chimps that encountered the snake made their own alert hoo, like a driver on Waze alerting others of a problem on the road. But chimps that thought their fellows were unaware of the road hazard made more alert hoo calls. They also stayed longer to look back and forth from the snake to where they thought their companions were. That’s the way chimps try to show their friends where a danger is.
The significance of the finding, Dr. Crockford said, is that it challenges the view that only humans keep track of what others know and change their communication to match. “This experiment shows they are monitoring their audience,” she said of the chimps.