into Sonso territory and our chimpanzees appeared frightened of them. We feared at that
time that all our males might be killed, and the females taken over by the Waibira males
from the north, as happened at Gombe when the Kasakela community attacked the
Kahama community further south (Goodall 1986). But this did not happen; there was a
considerable amount of illegal logging in the area between Sonso and Waibira and it
may be that the northern community was forced to move further north, away from the
loggers and away from our study community.
Second, the migration data confirm a feature of the behaviour of a few of our chim-
panzees, namely disappearance followed by reappearance. This was first noticed in the
behaviour of an adolescent female, Mukwano. Female emigration is the norm in the
philopatric society of chimpanzees. But Mukwano did not simply emigrate at adoles-
cence; she disappeared and returned. She was present from April 1992 when she was
first identified and named until March 1993, then she disappeared and reappeared
20 months later in November 1994. She has remained in the community since that time,
disappearing for short periods. In November 2002 she gave birth to a son, Monday, and
in April 2003 she disappeared with him, returning without him in July 2003.
A second chimpanzee to go missing for a while was Jogo. Jogo was a juvenile male
named in November 1992; he disappeared in October 1993 but reappeared in April
- He was around until October of that year, then disappeared again and was not seen
until March 1995, after which he resumed association with members of the community.
In April 1997 he disappeared and has not been seen since.
In September 1997, Emma immigrated into the Sonso community. At that time she was
a juvenile aged about 6 years. She remained in the Sonso community until January 2003
since when she has not been seen. Thus Emma emigrated at the age of around 12 years.
Another female, a subadult or adult whom we named Juliet in January 2002, had
immigrated into the Sonso community not long before. She remained at Sonso and had
her first maximal sexual swelling in January 2003. Soon afterwards she left the commu-
nity and has not been seen since. She was therefore in the Sonso community for around
a year.
These individuals who come and go may be following a strategy of belonging to two
communities, or it may be that they come to Sonso at a time when their normal home
community is undergoing some kind of trauma or disintegration and they move to and
fro before settling at Sonso.^9 In theory, females who move between two communities
increase the number of mating partners available to them. Alternatively, in theory,
females who move between two communities and become known to males in both can
avoid the danger of infanticide to their infants. We know from all other sites that
adolescent females frequently move from their natal community to another where they
settle and have their young. The only exceptions are certain high-ranking females who
remain in their natal communities, for example Flo at Gombe (Goodall 1986). At Sonso
there are some non-adolescent, parous females whom we know to have moved between
communities; we consider these cases in more detail in Chapter 5.
Community size 31(^9) I am grateful to Melissa Emery Thompson for this suggestion.