Before Sounding an Alarm, Chimps Consider the Knowledge of Their Audience

It's a basic rule of effective communication: Consider your audience. According to a new research report, that rule of thumb is not lost on wild chimpanzees.

Researchers now show that chimpanzees are more likely to make an alarm call about the presence of a snake when others in the group are unaware of the apparent danger they face.

The new findings suggest that chimpanzees keep track of the information available to other chimpanzees and make selective decisions about the messages they convey based on that understanding.

The results of this study conducted in the Budongo Forest, Uganda, from February 2008 to July 2010, were published in the December 29th issue of Current Biology .

The image is of a subadult male from the Budongo Forest, Uganda, vocalizing to other group members. A new study shows that chimpanzees produce a specific 'alert' call to threats, such as a deadly snake. They produce these calls more when audience members are ignorant, rather than knowledgeable, about the presence of the snake. This indicates that chimpanzees understand others' knowledge states and communicate missing and relevant information to ignorant others, a communicative feature previously thought to be limited to humans. Image credit and copyright: Catherine Hobaiter.

"Chimpanzees really seem to take another’s knowledge state into account," said Catherine Crockford of the University of St Andrews, UK, the first author. "They voluntarily produce a warning call to inform others of a danger that they do not know about. They are less likely to inform audience members who already know about the danger."

The researchers made the discovery by placing model snakes in the path of wild chimpanzees and watching their reactions. Those studies show that when an individual chimp detects a snake, they typically produce an "alert hoo" to tell the others they are with.  As new group members arrive on the scene, chimps in the know repeat their "alert hoo," filling in the newcomers that a snake is in their midst.

The findings challenge the notion that only humans recognize ignorance in others and act so as to fill them in, the researchers say. It also shows that chimpanzee vocalizations are influenced by a pro-social motivation, intentionally informing others of danger. It has been known that monkeys make inferences about the directedness of vocalizations even in the absence of visual cues.

The new findings are particularly noteworthy given debates over the role of mental state attribution in the evolution of language. "Some have argued that a crucial stage in this evolution occurred when individuals began producing vocalizations with the goal of informing and thereby reducing ignorance in others," Crockford says. The new findings show that "more of the ‘essential ingredients’ needed to kick start complex communication are evident in chimpanzees than we thought."

It's also key that the findings were made in chimpanzees in the wild, Crockford adds, noting that many earlier studies have been conducted in captivity.

"The advantage of addressing these questions in wild chimpanzees is that they are simply doing what they always do in an ecologically relevant setting, so the task is always relevant," she says.