length of observation until asymptote is reached and, however long observation continues,
no more individuals are encountered. This may take hours or days or even in some cases
longer, depending on the species, its dispersion pattern and the thickness of the vegetation.
In the case of fission–fusion species such as the South American red spider monkeys in
which groups constantly split up and re-form (Chapman et al. 1993) a new level of dif-
ficulty is encountered: where does the group begin and end? This is only solved after a
prolonged period of study, when the borders of the range of the animals are established.
In 1962 my wife Frankie and I spent 8 months watching chimpanzees in the
Busingiro part of the Budongo Forest. Jane Goodall was already working at Gombe in
Tanzania when we went to Uganda. Apart from an early study by Nissen (1931) in an
area of open country in Guinea, West Africa, during which sightings of chimpanzees
were few and far between, and a more recent one by Kortlandt (1962) in which he
watched, filmed and did interesting field experiments on chimpanzees in a populated
area near Beni in E. Congo, there had been no prolonged field studies of chimpanzees,
and none in the primary habitat of these apes, the rainforest. In our 1962 study, written
up as a book (Reynolds 1965) and in the form of a scientific chapter (Reynolds and
Reynolds 1965) we did not cut trails through the forest, which made finding and observ-
ing chimpanzees arduous. Despite this we obtained a lot of information and were able
to piece together the fission–fusion system of chimpanzees that had never before been
described, as well as their dietary preferences, their social and sexual behaviour.
When I returned to Budongo in 1990 the first priority was habituation. It took five
years of daily following and observing them by our field assistants and researchers before
we knew the number of chimpanzees in the Sonso community; or, to put it another way,
before the shyest individuals allowed us to observe them (Reynolds 1997/8). Our field
assistants were in the forest for 7 or 8 hours a day.^4 The first individuals they identified
were the big, confident males; later they made progress in identifying the females and
younger animals which were shy and disappeared at the first sign of human presence.
The process of discovering how many chimpanzees we had in our Sonso community
is graphically illustrated by Fig. 2.1. From this figure it looks as if the Sonso community
was growing over the first five years, but it was not: our knowledge of it was growing.
Let us consider this process in more detail.
As mentioned, one of our first actions on establishing the site at Sonso was to employ
four field assistants. These were Zephyr Kiwede, Geresomu Muhumuza, Dissan
Kugonza and John Tinka. I met them first in September 1990 when I returned to Uganda
after my initial visit in March of the same year. I was immediately struck by their lively
enthusiasm for the work.
By the end of 1992 we had identified 20 individuals. At that time we had no idea that we
had still named less than one half of the community. It was not until September 1995, three
years later and five and a half years after the beginning of the project, that we had identi-
fied, without knowing it then, all 50 of the chimpanzees living in the Sonso range at that
time. Some of the individuals in the Sonso community are illustrated in Figs. 2.3 and 2.4.
22 The Sonso community
(^4) Since January 2003 this has increased to 10.5–13.5 hours a day.