Chimps can "discuss" their favorite fruits and food sources

Chuck Bednar for redOrbit.com – Your Universe Online

Chimpanzees can modify their food call structure in relation to their favorite types of fruits and the size of the trees where those consumable can be found, according to new research published in the March 2015 edition of the journal Animal Behaviour.

The discovery was made by lead investigator Ammie K. Kalan of the Max Planck Institute for Evolutionary Anthropology, who along with co-authors Roger Mundry and Christophe Boesch observed wild chimps making context specific, acoustically graded vocalizations.

While monitoring West African chimpanzees, the trio of researchers found that they modified their call pitch according to tree size of a species of prized fruit known as the Nauclea tree fruit. Nearby chimps appeared to be attracted to calls produced for larger trees, the study authors said, and variation in the call structure could not be explained solely by increased arousal.

According to Discovery News, the study is the first to find that information about tree size and the amount of available fruit is included along with food quality assessments in chimp calls. The findings are based on more than 750 hours of observations conducted in the Ivory Coast.

“Chimpanzees definitely have a very complex communication system that includes a variety of vocalizations, but also facial expressions and gestures,” Kalan told the website.

“How much it resembles human language is still a matter of debate, but at the very least, research shows that chimpanzees use vocalizations in a sophisticated manner, taking into account their social and environmental surroundings,” she added.

Kalan, Mundry and Boesch found that higher-pitched calls were produced when the West African chimps encountered fruits from Nauclea trees. Smaller trees elicited even higher pitched calls, while larger trees with more fruit tended to be somewhat lower in pitch.

“I never tried these fruits myself,” Kalan said, “but they do smell very good in the forest.” She added that these fruits “are also quite big and easy to ingest, and we also know that they have a high energy content, which is important for wild animals.”

The researchers analyzed a total of 379 food calls produced for five different food species. They said that additional work will be required to determine whether or not variation in food call pitch can influence the foraging behaviors of the recipient, but they believe that understanding the data encoded in those variations represent some degree of flexibly modulated vocal communication.

“Chimpanzees are incredibly social beings, and sharing food is just one way of many that individual chimpanzees can solidify relationships within their group,” Kalan said. “Calling for one another at a food tree is one way that they can attract other chimpanzees in order to meet up with members of their group that they have not seen for a while.”

Klaus Zuberbühler, a professor in the School of Psychology and Neuroscience at the University of St. Andrews who was not involved in the study, told Discovery News that “have shown… that (chimp) call structure changes, not only in response to the food type, which was already known before, but also in relation to the size of the tree, a new finding.”

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