Scientists have discovered that chimpanzees use different calls when eating different foods – and that fellow chimps can understand exactly what they mean.
The finding, by primate experts at the University of St Andrews, is the first evidence of this type of vocal communication in apes and important for the study of the evolutionary origins of speech signals. Previous studies of apes have provided insights into the evolution of communication by gestures but not speech.
The researchers studied chimpanzees living at Edinburgh Zoo, hoping to establish whether chimps made different ‘rough grunt’ calls when they found either high value or low value food. The researchers, Katie Slocombe and Klaus Zuberbühler, discovered that the chimps made high grunts when they found bread (high value) and low grunts when they found apples (low value).
Their goal was to determine whether other chimps would understand what the calls meant, and whether they would use this information to find food themselves. During playback of the calls, the researchers found a chimpanzee apparently recognising the calls for separate food types and searching in the appropriate places for the food himself. The chimpanzee searched more intensively and for longer in the correct place after hearing the corresponding call.
Katie Slocombe said: “This is the first demonstration that chimpanzee calls function to refer to the nature of discovered food and these calls are meaningful to fellow animals. It shows that, by simply listening to each other’s calls, chimpanzees can infer what kind of food the caller has found. Our focal animal adjusted his foraging behaviour on the basis of the calls he heard.
“We don’t know yet how specific these calls are, i.e. whether they specifically refer to ‘bread’ or ‘apples’, or whether they simply label highly preferred food (the bread) and less preferred (the apples) food types. We are planning further experiments to test these two possibilities.”
The calls are a demonstration of ‘functionally referential’ signals, animal signals that are reliably given in response to an external event or object, such as a particular predator or food. Although functionally referential communication has been found in monkey species, until now there has been no evidence for this in any of the great apes. This is surprising given that apes are cognitively more advanced than monkeys and more closely related to us. This study provides the first experimental evidence that our closest living relatives can produce and understand functionally referential calls as part of their natural communication.
The researchers believe that the calls must have a social function since chimps rarely produce rough grunts when eating alone. Previous observations in the wild have shown that chimps only produce grunts when another individual approaches.
Dr Zuberbühler said: “Chimps may find it genuinely unpleasant to eat without others doing the same. The same seems to be the case for humans. We don’t like to eat in the presence of others who are not eating. In many cultures humans coordinate the timing of starting a meal, for example with vocal cues such as ‘bon appetit’.”
“These ‘rough grunt’ calls are specifically produced when chimpanzees find food. Subtle but consistent acoustic variation is present within this call type and this study indicates chimpanzees use this variation to indicate the presence of different foods. This study is special because it provides the first evidence that listening chimpanzees are sensitive to this variation: they seem to understand that the calls refer to the food encountered by the caller,” he explained. The study is published in the journal Current Biology this week.
NOTE TO EDITORS:
THE RESEARCHERS ARE AVAILABLE FOR INTERVIEW:
Katie Slocombe -Tel: 01334 467279 or email firstname.lastname@example.org
Klaus Zuberbühler – Tel: 01334 462080 or email kz3@st- andrews.ac.uk
NOTE TO PICTURE / SOUND EDITORS:
CHIMPANZEE IMAGES AND SOUND FILES OF THE DIFFERENT GRUNTS ARE AVAILABLE FROM THE PRESS OFFICE – CONTACT DETAILS BELOW.
Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook, Press Officer on 01334 467227 / 462529, mobile 07900 050 103, or email gec3@st- andrews.ac.uk Ref: Language of Food 131005.doc View the latest University press releases at http://www.st- andrews.ac.ukResearch