In support of this, Fawcett did not find evidence that females competed for core areas
in the centre of the range. In contrast with the situation at Gombe (Goodall 1986), older,
higher ranking females at Sonso did not have core areas in the middle of the community’s
range, with lower ranking females on the periphery. Nor did adolescent or young adult
immigrant females establish core areas on the periphery, they moved into the centre of
the range with the resident adult males and females, sometimes using maximal sexual
swellings as a ‘social passport’ (Boesch and Boesch-Achermann 2000).
Newton-Fisher (2000) concurs that while both males and females at Sonso have core
areas or ‘preferred’ areas of activity, these areas are not exclusive and overlap exten-
sively. He found that males spent most (80%) of their time in their core areas, moving
out for occasional territorial behaviour or for peripheral food sources. In the case of
females, the same was true but they moved out when in oestrus for purposes of joining
parties with adult males. To test whether good food supply was responsible for males
having core areas Newton-Fisher compared them with surrounding areas and found no
difference.^41 Nor did they appear to be related to male rank. He suggests that they may
have territorial functions as zones of safety, and social functions as areas where alliance
partners can be located.
Inter-community movements of adult females
Reference to certain adult females as ‘immigrants’ makes the assumption that they have
come from another community. An alternative explanation is that some or all of these adult
females are not immigrants but are ‘peripheral’ females who have not hitherto made their
presence known to observers because of extreme shyness, so that when they move into the
centre of the range and we see them for the first time it is a case of ‘coming out’ within
the community rather than entering the community from another one. Harriet, for
instance, was first seen with her juvenile Hawa in 1996, since when she has always been
a rarely seen individual who pops up from time to time. In 1996 the Project was still
young and it is unclear whether she was an immigrant or a previously unrecognized
individual. It is also possible some females come and go between communities.
Mukwano, a well integrated and easily seen female, twice disappeared and we concluded
she had emigrated or left the Sonso community. The first time this happened, when she
was a subadult, we did not see her for 20 months; the second time when she was an adult
with a son, Monday, for a shorter period during which she lost her infant son in
unknown circumstances (perhaps as a result of infanticide), returning without him.
The arrival of Melissa with her juvenile son Mark, Sabrina with her juvenile daugh-
ter Sally, and Wilma with her juvenile son Willis, who arrived in quick succession^42 in
October–November 2001, took all observers by surprise. Of these three new adult
females, only one, Sabrina, is suspected to have been seen before, for a short time one
104 Social organization
(^41) This is not to say that core areas elsewhere are not related to food supply, which may indeed be the case,
as for example in the case of female core areas at Gombe. 42
Melissa was first seen on 15 October 2001 and Wilma on 16 October 2001 and Sabrina on 3 October
2001.