on her vagina as if she was waiting for something. KY repeatedly touched her vagina and moved
about in the tree, changing from one branch to another. At 09:12 she started showing abdominal
contractions with the right (functionless) hand placed on the vagina.
At 09:22 the vagina opened widely: the infant’s head was seen to come out first. The infant
emerged fully at 09:23:20 and KY caught it with her left hand. She immediately pulled the infant on
to her belly and hugged it...At 09:40 the placenta emerged, KY moved her left hand to her vagina,
collected the placenta and started to feed on it immediately. At 09:46 she finished feeding on the pla-
centa and started licking blood from her hands. She did not eat the umbilical cord and she left it hang-
ing. At 09:48 she grasped the umbilical cord from the distal end and started pulling it. At 09:48:30 she
was seen biting the umbilical cord. At 09:49 she stopped and after 30 seconds she started feeding.The social aspects of this birth are interesting and we shall return to them in Chapter 5.
For the moment the following aspects are of note:
● the mother was nulliparous yet fully competent before, during and after the birth;
● this was true despite that she had only one functional hand (the left);
● despite this she gave birth 30 m up in a tree;
● the placenta was eaten within 25 min of the birth, earlier than appears to be the case
at Gombe (Goodall 1968: 223).
Age and age groups
How long do chimpanzees live? From our Sonso data we do not know. Goodall (1986),
Nishida (1990) and Boesch and Boesch-Achermann (2000) give figures of 42–44 years
of active life and the possibility of survival up to 50 years, and there seems no reason not
to accept these figures for Budongo.
We know accurately the ages of the individuals born into the community. The ages we
have allocated to our older animals, those already in the community when we began our
studies, are approximate and are the result of two processes: comparison with chimpanzees
at other study sites where ages are known; and intra-community comparisons, i.e. deciding
on the basis of darkness of the face (chimpanzees’ faces become darker with age), graying
hairs on the back (chimpanzees go grey around the rump as they get older), vigour and
musclemass (chimpanzees tend to suffer from muscular wasting as they get older).
Applying these principles we can age the individuals in our Sonso community with
reasonable accuracy. Dates of birth, known and estimated, together with margins of
error, are given in Appendix A.
For most purposes of analysis, age groups suffice. At Sonso we distinguish the
following age groups: Adult, Subadult, Juvenile and Infant. We categorize and define
these age groups as shown in Table 2.3.^11 These definitions have been arrived at by
Age and age groups 35(^11) This table was revised in December 2003. I am grateful for help provided by S. O’Hara, C. O’Hara,
M. Emery Thompson and L. Bates.