reference to the categories used by other field workers, e.g. Goodall (1986), Boesch and
Boesch-Achermann (2000) and Kawanaka (1990). The object is not just to reflect dis-
tinct changes in the life cycle but also to make the Sonso categories comparable with
those of others to enable cross-site comparisons to be made.
Infertility
There is for all female chimpanzees a period of adolescent infertility^12 when they
nevertheless show sexual swellings. Evidently the senior males are aware of the dis-
junction between these early swellings and infertility because they take little interest in
such females. This period was most marked in the case of Kalema, a late juvenile female
at the start of our study. Kalema was continually swollen for 873 days (2 years 143
days), from 8 July 1992 to 30 November 1994. Her swellings waxed and waned from
stage 1 (small) to 4 (maximal) during this period but never disappeared (stage 0).
Although Kalema and her age-mate Kwera (whose swellings began at the same time as
Kalema’s and were irregular but not constant like Kalema’s) stayed away from parties
containing adult males and kept very much to themselves, the males took little sexual
interest in either of them. However, the adult male Maani was observed copulating with
Kalema on 19 April 1994. We know from subsequent genetic studies (see Appendix C)
that Maani was not the father of Kalema’s subsequent infant but it was around that time
that she conceived (by the adult male Black). Kalema continued to show swellings dur-
ing her pregnancy, she was maximally swollen on 30 November 1994, showed a
reduced swelling (stage 2) on 2 December 1994, and within two weeks had given birth
to a daughter, Bahati, first seen on 16 December 1994. After the birth her swellings
ceased. Her age-mate Kwera kept in parallel giving birth to a son, Kwezi, on or around
7 January 1995, the father being Muga, the son of the alpha female Nambi.
36 The Sonso community
Table 2.3: Age categories.
Age Sex Age where Alternative criteria where age
category known not known
Infant Both sexes Birth to end of 4th year Dependent on the mother
Juvenile Both sexes 5th to end of 9th year Increasing independence from mother
Subadult Male 10th to end of 15th year Beginning to increase in dominance
Testes becoming larger
Female 10th to end of 14th year Sexual swellings begin, may be irregular
No offspring yet
Adult Male 16 years Testicular development complete
Face black
Dominates females and
challenges males
Female 15 years Normally has offspring
(^12) Nishidaet al. (2003) found the median length of this period in four females at Mahale to be 2.8 years.