HOPE Report No.15, 24th, February 2005.

Program No.15 (facilitation of exchange between young scientists)

Yukiko Shimooka : Research Associate, Primate Research Institute, Kyoto University

Place of visit : Kalinzu Forest, Republic of Uganda

Title of Research : Do chimpanzees change the frequency of vocal emission at feeding trees depending on the amount of fruits or the preference of the fruits?

Period of visit : 8 January - 8 February 2005

Chimpanzees have various types of vocalization and each type of vocalization is produced at different context [Goodall 1986; Marler and Tenaza 1977]. Among variable vocalizations, food-grant and pant-hoot are produced in association with feeding [Marler and Tenaza 1977]. [Hauser and others 1993] conducted an experiment in captive chimpanzees, and found that the number of "food-grant" and "pant-hoot" given by chimpanzees increased whe they were presented larger amount of food and divisible food.

 Although food-grant was emitted at any condition of food presentation and was likely to be a functionally refetential signal to food, pant-grant was emitted only when the amount of food was quite large, and was likely to encode the information about the caller's generalized arousal. In this study, I examined the influence of quantity of food at feeding trees on calling behavior of wild chimpanzees, especially on the production of food-grunt. Farthermore, I examined the influence of vocal production at feeding trees on not only party joining, but also the number of individuals gathered in one feeding tree.

The preliminary result of analysis suggests that the frequency of food-grant emission is related both with the food species and the amount of fruits in the feeding tree. In the study period, they mainly foraged five species of fruits: Pseudospondias microcarpa, Syzisium guinensis, Ficus natarensis,Ficus saussuriana, Musanga leo-errerae. Among these five species, mean vocal frequency of food-grant per individual varied from 0.35 / tree at Musanga to 3.74 / tree at Syzisium.

It is likely that chimpanzees emit more food-grants at the preferable food species, especially when there are many mature fruits in the feeding tree.


An adult male of chimpanzee, eating vine leaves. 


Two males in grooming-hand-clasp.