The #1 source for news about monkeys and apes

[Carrie McLaren <stay.free AT verizon.net>]

Chimp "Dinner Conversation" Proof of Ape Speech?
Adrianne Appel
for National Geographic News
October 20, 2005
http://news.nationalgeographic.com/news/2005/10/1020_051020_chimps_talk.html

Scientists say they have discovered the first evidence that 
chimpanzees speak to each other about objects in their environment.

Chimps at the Edinburgh Zoo in Scotland use a crude language of 
grunts to talk to each other about their food, say primate experts at 
the University of St. Andrews in Scotland.

The chimps utter high-pitched noises (hear the audio) or low-pitched 
grunts (hear the audio) to tell each other about the food they find 
in their pen, the researchers say.

The finding could lead to better understanding of the origins of 
human speech, the scientists say.

Previous studies have found that monkeys, as opposed to apes, 
communicate with each other through sound about events in their 
environment and that great apes can use hand signals. The new chimp 
finding, however, may be the first evidence of great apes using vocal 
communication.


Bread Good, Apples Bad

At the Edinburgh Zoo the chimps make high grunting noises when they 
find bread, a food they seem to like, and low grunting sounds when 
they find apples, which they apparently don't care for very much, 
according to the study, published last week in the journal Current 
Biology.

After noting the different types of grunts, the researchers set out 
to see if other chimps listening to the grunts interpreted them the 
way the researchers had ("bread" and "apple"). The researchers found 
that the listening chimp did seem to understand what the grunts mean.

The scientists recorded the grunts and played them to a chimp in the 
pen. When the chimp heard the "bread" grunt, the ape looked in the 
place in the pen where bread is usually found. When the "apple" call 
was played, the chimp searched appropriately for an apple.

"It shows that, by simply listening to each other's calls, 
chimpanzees can infer what kind of food the caller has found," said 
researcher Katie Slocombe, who worked with colleague Klaus 
Zuberbuhler on the project.

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 [such as bread] and less preferred food types 
[such as apples]. We are planning further experiments to test these 
two possibilities," Slocombe said.

In research terms, the grunts are known as functionally referential 
signals: signals that animals give to each other in response to an 
outside event or object, such as an alarm call that warns of a 
predator.

"These 'rough grunt' calls are specifically produced when chimpanzees 
find food," Zuberbuhler said. "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 added.

Debby Cox, the Jane Goodall Institute's executive director for 
Uganda, said the chimp grunting research is "just the beginning."

"It's a no-brainer that they're going to have high grunts for highly 
prized food. It's the same with people," Cox said from the 
institute's Arlington, Virginia, headquarters. "Chimps are very 
motivated by food. In any research we use food as a reward."

That's not to say the new findings aren't surprising. "If other 
chimps recognize the high grunts, that's something that hasn't been 
looked at before,'' Cox said.

Also, "if specific grunts identify a specific food, that is something 
we haven't seen before," Cox said.

Dinner Bell

Study co-author Zuberbuhler believes that the grunts serve a social 
function, since the chimps hardly ever make the noises when they are 
eating alone.

The grunts may be a call to dinner, Zuberbuhler says. "Chimps may 
find it genuinely unpleasant to eat without others doing the same."

The Jane Goodall Institue's Cox has observed different behavior among 
chimps, however. "I'm not sure that I agree with chimps not grunting 
when they're alone. When infants, they grunt when we offer them food, 
but maybe that's because we're considered parents," Cox said.

The possible dinner-bell grunts may be related to certain human 
vocalizations, Zuberbuhler said.

"We don't like to eat in the presence of others who are not eating," he said.

"In many cultures humans coordinate the timing of starting a meal, 
for example, with vocal cues such as 'bon appetit.'"