Article and photo courtesy of The Jane Goodall Institute

May 28, 2005 — Just as Jane Goodall took to the jungles of East Africa in 1960 to study chimpanzee behavior, another young woman inhabited Uganda's Budongo Forest in parts of 2003 and 2004 to research chimpanzee vocalizations. Her studies, which have identified two new calls, could help us understand the evolution of human communication.

Katie Slocombe, a Ph.D. student at St. Andrews University's Center for Social Learning and Cognitive Education, conducted research in Budongo Forest in western Uganda, studying the chimpanzees for eight months in total. She also observed chimpanzees at the Edinburgh Zoo.

In Budongo, Slocombe tracked down parties of chimps each day, gathering data on members of the "Sonso" community. Following a chimp through the dense, dark jungle was no easy task.

"The research was very interesting and enjoyable, but it was also challenging on a number of different levels," she said. To begin with, the temperature at Budongo upon her arrival was 35°C (95°F), a far cry from the 5°C (23°F) she left behind in Scotland. Then there were the biting ants, stinging caterpillars, strenuous walking required to keep up with chimps and the fact that the dense foliage made spotting chimps difficult.

"The visibility in the forest was very low in parts," she said. "It was vital to be able to see the behavior of the vocalizing individual in order to record a detailed context for the call."

Often this was impossible. "Many times ... the undergrowth was too thick and the chimpanzee was moving too fast to be able to get a good view of what was happening. This certainly reduced the amount of useable data I was able to collect."

One of the more complicated parts of her research was capturing the calls of the chimps efficiently. "In the beginning," she said, "it was very frustrating — repeatedly missing vocalizations. It took time to be able to anticipate the vocalizations and react quickly enough in order to capture them with my sound equipment."

As her understanding of the chimps increased, so did her ability to anticipate their calls.

The vocalizations themselves, however, presented another challenge. The human ear is not a good tool for identifying the complex acoustic structure of chimp calls. Another method for classification is needed.

"Armed only with Dr. Goodall's descriptions of the calls, it was very difficult to classify some of the calls, as they all grade into one another," Slocombe explained. "One thing that is sorely needed, and (that) I would love to one day accomplish, is an objective acoustic classification of the chimpanzee vocal repertoire."

Although Slocombe said such a classification is years away, the finished product would detail acoustic information showing one call type to be measurably different from the other types. This would be accompanied by a detailed description of when these calls are used, mimicking Goodall's own classification system.

Another challenge was identifying the chimps by sight. Although aided by a field assistant who was expert at telling them apart, it was important to Slocombe that she could identify them herself. With a background in studying captive chimps, she was not used to having to identify chimps on the move through thick undergrowth.

Fortunately, her ability to recognize individuals came with time. The study community of chimpanzees contained about 60 members, most of whom Slocombe could identify upon her departure.

Acoustic analysis

As she overcame the obstacles of working in the jungle, she took an interest in collecting data on the more subtle vocalizations, although she has only scratched the surface of these subtleties.

After eight months of recording the sounds and behavior of the chimps, Slocombe headed back to St. Andrews to begin the laborious process of analyzing the data.

The analysis involved examining the acoustics and statistics of the data. Researchers had to test if the chimps reliably gave acoustically distinct calls in specific contexts. The sound as well as the regularity of the calls was important.

"I started by looking at the screams the chimpanzees gave when they were involved in agonistic interactions," she explained. The work is still ongoing, but Slocombe has already found two new types of screams.

"Chimpanzees give different screams depending on their role in an agonistic interaction. Screams given by victims and aggressors had subtly different acoustic structures."

These different screams were consistent for all chimps studied. Fourteen individual male and female chimps, ranging in age from seven to 35, all vocalized in the same way during fights.

From this, Slocombe suggested that specific screams may serve to inform other chimps within earshot, but not within sight, of what is happening in the fight.

"Listening chimpanzees may be able to extract important social information from the screams, such as the role the caller has in the interaction," she explained. "This could influence their decision as to whether approach and intervene."

Although the observations point to this being true, further study must be done to draw firm conclusions.

What are the potential benefits of Slocombe's research?

"As language is one of the key abilities which distinguishes us from the rest of the animal kingdom, an evolutionary explanation for this complex ability is of enduring interest," Slocombe said.

In addition, the vocalizations of chimps are an essential part of chimpanzee behavior, as sound is often their only source of information.

"Given the low visibility in their natural environment, vocal communication seems to be a very important modality for communication in chimpanzees. If we understood their vocal communication better, it would help us make sense of many other behaviors."

The research also has some possible important practical applications. "The more we can reveal about the complexities of chimpanzee behavior, the better we can care for them in captivity, and the more chance we have of persuading the world how imperative protection of this species in their natural habitat is."

To read more about Katie Slocombe's work and that of St. Andrew's Center for Social Learning and Cognitive Education, click here.