study using three methods of analysis (minimum polygon, fixed kernel and adaptive
kernel), as between 6.78 and 14.51 km^2 , giving a density for the 46 individuals in
the community at that time of between 6.8 and 3.2 individuals/km^2. This is somewhat
higher than the density estimate of 3.9/km^2 we found for Busingiro by our much cruder
method, and is likely to be more accurate.^6
It is also higher than the density found for the whole of the Budongo Forest. Andrew
Plumptre conceived the idea early in our research of making a study of the whole of the
Budongo Forest and of including in this a survey of the chimpanzees of the forest, based
on nest^7 counts. The survey was carried out in 1992 and was the first accurate survey of
chimpanzees in a large area (previously, single communities had been counted accu-
rately but not larger areas), and all the more remarkable for being in a forest habitat
(Plumptre and Reynolds 1996). With expertise based on his own prior survey work on
gorillas, Plumptre organized our field assistants to conduct transect-based counts of
nests in eight areas of the forest. These areas were chosen to represent the different
forest types and the logging history of the forest. Analysis of the results using adjusted
‘standing crop’ counts gave a figure of 650–890 chimpanzees for the whole forest,
giving a density of 2.12–2.22 individuals/km^2.
We can also draw a comparison with Kibale Forest, to the south of Budongo in
Uganda. Range use by the Kanyawara community was studied there by Chapman and
Wrangham (1993). Using three methods (minimum polygon and two sum-of-cells
methods) they calculated the home range as 7.8–14.9 km^2 , giving a density for the
41 individuals in the community of 5.2–2.75 individuals/km^2. This again is somewhat
lower than Newton-Fisher’s density for Sonso.
The higher density found by Newton-Fisher (3.2–6.8 individuals/km^2 ) than by
Reynolds and Reynolds (1965) and Plumptre and Reynolds (1996) suggested to him that
the area of the Sonso community might be particularly rich in chimpanzee foods, and
there is support for this as we shall see in more detail in Chapter 4. Another reason given
by Newton-Fisher for the higher density of the Sonso chimpanzees is the relatively
lower level of timber exploitation at Sonso compared with Busingiro, and here again he
may well be right. At Busingiro both at the time of our study in 1962, and at the time of
the later studies in the 1960s, there was a considerable amount of legal and illegal
pitsawing for mahogany going on (as it still does today). This has not been the case in
the Sonso area during our studies from 1990 onwards, mainly because the presence of
the BFP has tended to keep illegal pitsawyers away from our study site.
Range and density of the Sonso community 29(^6) All measures of home range (or total range) are necessarily estimates (N. Newton-Fisher, pers. comm.).
(^7) The word ‘nest’ to describe the structure made by chimpanzees each night and sometimes in the daytime
has been criticized by Prof. Toshisada Nishida (pers. comm.), who prefers the word ‘bed’. Indeed there are
problems with the word ‘nest’, which in many species signifies a structure made to lay eggs or rear young.
This is not applicable to chimpanzees. However, the word can also mean a retreat or a place of safety. The
Oxford English Dictionary, after the first definition which is a place for rearing young, gives a second defini-
tion as follows: ‘A place in which a person (or personified thing) finds rest or has residence; a lodging, shel-
ter, home, bed etc., especially of a secluded or comfortable nature; a snug retreat.’ This seems to cover the
chimpanzee case. For that reason, and because the word ‘nest’ is widely used in the literature on the subject,
I have maintained this usage here.