HOPE Report No.15, 24th, February 2005.
Program No.15 (facilitation of exchange between young scientists)
Yukiko Shimooka : Research Associate, Primate Research Institute, Kyoto
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
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
An adult male of chimpanzee, eating vine leaves.
Two males in grooming-hand-clasp.