Chimps Name Foods With Grunts

Nov. 28, 2006 — Whales do it. Chickens do too. And now chimpanzees can be added to the list of animals that appear to produce distinctive word-like calls for specific things, according to a study in this month’s Animal Behavior.

If such vocalizations indicate what’s on the animals’ minds, then for zoo chimps it’s bananas, mangos and bread. Researchers Katie Slocombe and Klaus Zuberbühler discovered that captive chimps likely create referential, vocal labels for these particularly coveted foods.

"Our analyses surprisingly showed that grunts to banana, bread and mango were acoustically distinct," Zuberbühler, a researcher in the School of Psychology at the University of St. Andrews in Scotland, told Discovery News. "It is very possible, therefore, that recipients can use this information to draw inferences about the type of food encountered by the caller."

The scientists studied 11 chimpanzees at the Edinburgh Zoo, as well as a community of chimps in the wild at the Budongo Forest Reserve, Uganda.

For each group, the researchers first identified the chimps' favorite foods. For the zoo animals, the scientists were even able to determine their medium-preferred foods (grapes, plums and chow) and their least faves among food regularly offered (apples, greens and carrots). The wild chimps seemed to feed most often on certain trees, including a type of uncultivated fig tree.

The scientists next recorded the "rough grunt" calls the chimps emitted when they encountered the foods. Computer analysis of these sounds revealed the zoo chimps repeatedly produced specific sounds linked to their food faves, but that other calls were less distinctive.

"Grunts to highly preferred foods are more tonal and therefore easier to analyze," Zuberbühler explained. "Hence, we cannot rule out that similar effects were also present within the medium and less preferred food items, but our acoustic analysis just did not pick it up."

While the scientists couldn’t duplicate their findings for wild chimpanzees, they determined both captive and wild chimp calls were very similar, which Zuberbühler said suggests "they are part of a universal chimp communication system when dealing with food."

Previous research has found that chimps also produce distinct vocalizations when they encounter snakes, bullies, chimp victims and when they are hunting, suggesting chimp vocabulary covers more than just food.

The researchers theorize captive chimps may have a greater gift for food gab because they encounter the same foods all of the time.

Vocal labeling presumes frequent prior exposure to the items in question, along with some need to share information about the items with others. For example, chimps, like humans, might benefit from sharing tasty foods with relatives, friends and potential mates.

Christophe Boesch, professor and director of the Max-Planck Institute for Evolutionary Anthropology in Germany, indicated to Discovery News that he agreed with the findings. Boesch, however, argues that wild chimps also label foods.

"Cathy Crockford and (myself) have demonstrated the use of context-specific calls in wild chimpanzees," Boesch said.

When it comes to chimp's volcalizations, Zuberbühler believes there is much more to learn.

"Not much work has been done on the vocal behavior of chimps, our closest living relatives," he said, "so we may be waiting for a few surprises in the near future."