Sonso culture 83There are many cultural items at Sonso that need further attention. ‘Groin-tuck’ and
‘neck-tuck’ occur when a small branch with leaves is tucked into a body fold while the
animal is resting, grooming or feeding, and then carried from place to place if the indi-
vidual moves; it is carried manually while walking quadrupedally or in the groin if
brachiating. If this behaviour has a function we have yet to discover what it is, though a
connection with nest-making was suspected on one occasion, observed by Lucy Bates
(pers. comm., 24 February 2003): two juveniles and an infant, Beti, Rose and Janet,
were playing with the leaves of a Cordiatree, breaking off the tips of branches. All three
individuals tucked the branchlets into their groins as they brachiated and held on to them
as they moved around in the tree. Rose used hers to begin a day nest, at which Janet, who
had dropped her leaves, began to pull at Rose’s nest. Janet reached out and tried to hit
her, no physical contact was made and Janet moved away and initiated play with Beti.
After a short while both Janet and Beti picked leaves, groin-tucked them, and added
them to the leaf-nest-pile started by Rose.
Sometimes the branchlet is draped around the back of the neck and a version of it
(‘pearl necklace’) was seen when the branch was from a fig tree. Many individuals have
engaged in this behaviour at Sonso.^24
The Sonso chimpanzees also eat the woody pith of dead Raphiapalm trees, but in a
very strange fashion: they make a hole in the bottom of the dead tree trunk while it is still
standing in the swamp forest, and gradually increase the size of this hole until it is big
enough for small chimpanzees to crawl into it. All the woody pith is extracted with the
hands and teeth, and chewed thoroughly in the mouth before being spat out in the form
of a bolus or wadge. Is there any alcohol in it? The pith of this species of tree is used by
local people to brew palm wine but only when the tree is freshly felled. Is there still a
remnant of alcohol in the dead trees? If so it would be a first observation of alcohol con-
sumption for chimpanzees. Certainly they have something in common with humans
drinking alcohol in that pith-eating is popular and individuals compete with each other
for access to the tree. As before, this behaviour has been filmed by Sean O’Hara.
In regard to vocalizations, we shall see in Chapter 6 a number of cultural variations
between the structure of calls at Sonso and the same calls at other field sites.
In Chapter 3 we discussed the health of the Sonso chimpanzees and their use of
Aneilema aequinoctialefor self-medication. Learning which plant species to use, which
occurs when infants watch their mothers self-medicating, is a cultural process, and we
know that the plants used by chimpanzees for self-medication differ from site to site
(Huffman 2001).
Tool-use, as stated earlier, is minimal at Sonso. A clear demonstration of this is the
way our chimpanzees eat termites. They break open the mound with their teeth and
hands, then eat termite soil and termites with their mouths. They eat honey without
using a stick to probe the nest, just breaking into it with hands and teeth. Use of a stick
has been seen several times as an invitation to play.^25 Nest-making involves a complex
(^24) This and several other items of Sonso culture have been photographed and filmed by Sean O’Hara.
(^25) This does not occur at Mahale (T. Nishida, pers. comm.)