Demographic structure
What conclusions can we draw from the demographic structure of the Sonso community?
Perhaps the most important thing in the long run for any community whether of chim-
panzees or humans is its productivity, the number of surviving offspring. The structure
of the Sonso community at the time of writing is as follows: 11 adult males, 19 adult
females, 5 subadult males, 5 subadult females, 4 juvenile males, 7 juvenile females, 3 infant
males, 7 infant females, plus one newborn not yet sexed. Total: 62 individuals.
At the time of writing we have more female infants (7) than male infants (3) which is
not good. If all our young females emigrate when they reach adolescence this will seri-
ously deplete the community, and the lack of males will weaken the community’s
strength. Infant males provide the future core of the community, its defence against any
ambitious neighbours who may in the future mount raids on Sonso. This has been the
pattern at Gombe (Goodall 1986) and Mahale (Nishida 1990; Nishida et al. 2003) where
studies have gone on for three or four decades, though it has not happened at Taï in West
Africa (Boesch and Boesch-Achermann 2000). Since the deaths and disappearances of
seven of our adult males referred to above, the Sonso community is already rather weak
numerically. There are nearly twice as many adult females (19) as adult males (11)
largely due to the high male mortality referred to earlier in this chapter. An excess of
females is a feature of the Taï Forest community and also of Mahale, so our Sonso com-
munity is coming to resemble these. Inter-community strife is not a feature of the Taï
chimpanzees, but it is of Mahale, and we have seen evidence of it in Budongo.
Males who go missing temporarily
On a number of occasions, adult males have gone missing for days or even weeks at
a time, and then returned. We have never discovered where they have been. These cases
are not thought to be consortships with females in the Sonso community since evidence
of missing adult females is lacking. However, we have shreds of evidence that females
from other communities may be involved. Bwoya (BY), a fully adult central Sonso
male, disappeared from 22 September to 26 October 1999. He disappeared again on
10 November 1999, last being seen with an unidentified female in full oestrus, heading
southeast. He was seen in Sonso again on 5 January 2000. Nkojo, another central male,
had a series of disappearances in 2001–2002. He was frequently seen until 31 March
2000, after which he was seen on the following days only (he would normally be seen
most days): 26 April, 30 May, 8 June, 20 June, 17–22 July, 29–30 September, 1–24
November, and then in 2001 11–18 January, after which he was seen regularly again. In
such cases we have little idea what these lone male wanderers get up to. On 15 August
2003 Nkojo, who had become a full-time resident again, was seen for the last time; he
has not been seen since and is now presumed dead, though there is a slender chance that,
with his history of short-term disappearances, he may yet be found alive one day.
Males who go missing temporarily 37