Chimpanzees Behavior

The study conducted by Slocombe and Zuberbuhler on food-associated calls in chimpanzees contained two interesting hypotheses. The first one states that the various vocalizations that are produced by these chimpanzees upon finding food are based on the three types of food preference groups that rank from high to low. The second hypothesis says that these sounds made when the chimpanzee encounters the food label particular food types.

These hypotheses were tested on both wild and captive chimpanzees using two distinct methods. First, the psychologists observed 53 wild chimpanzees of all different ages and sexes in the Budongo Forest over a period of six months (January-March). During this time they found that the three most chosen foods of the animal were bread, mango and banana, and they were put into the high preferred category. They then did the same thing for both medium and low preferred foods. In the second study, for a period of four months (May-September) the psychologists tested 16 captive chimpanzees of different ages and sexes in the Edinburgh Zoo. During this time, they were fed 9 different food types, which included bread, banana, mango, grapes, etc. at various times. The choices that they made as to which food they preferred were filmed and recorded. In order to figure out if the grunts were labeling specific food types, the psychologists controlled preference by putting them into categories of high preferred to low preferred foods and then listened to the grunts within each preference category. Both studies focused and analyzed the calls of four chimpanzees to see if they were a product of food preference or food type and the results are as follows.

For the first hypothesis regarding food preference, the psychologists discovered that both wild and captive chimpanzees had very similar results in the vocalizations produced in accordance to each category, with only some significant differences between the foods in the highly preferred food group. The results show that for high preferred foods, the acoustics were long with a high peak frequency, but for low preferred foods the acoustics were short and had a low peak occurrence. Therefore, their hypothesis that the rough grunts varied according to food preference groups is supported, and it was established that there is a positive correlation between peak frequency and preference. For example, for high preferred groups of food the mean peak frequency was 2.23 and for low preferred groups was .39. The results for the second hypothesis that these grunts labeled specific food types were not as consistent between both wild and captive chimpanzees. They found that the grunts produced by both wild and captive chimps when given high preference foods were slightly different, but within low and medium preferred foods there was no clear evidence of different acoustic