trees. Polystatic nests, made by both sexes, used two or more branches to provide
support. They were of two subtypes, ‘tension’ nests, made by pulling two or more
saplings together and then interweaving their crown branches, or ‘suspension’ nests,
made by bending a small branch down to rest upon a larger branch; the smaller
branch provided most of the nesting material while the larger branch acted as the
structural support.
In this study, males nested slightly later than females on average (mean 18.21 for
males, 18.18 for females, non-significant) with a negative skew for both studies, some
chimpanzees nesting as early as 17.00. Both McVittie’s and Brownlow’s studies found
that over 30% of nests were constructed between 18.45 and 18.59, roughly correspond-
ing to sunset.
Ground nests were found by Reynolds (1965), McVittie (1998) and Brownlow et al.
(2001). They appear to be a regular, if not common occurrence in Budongo. The case
described by McVittie concerned the adult female Kewaya (KY) who was in oestrus and
the adult male Kikunku (KK). At 18.00 on 22 May 1998, KK was observed shaking
small saplings to indicate his interest in KY. Both individuals were feeding on ground
vegetation. At 18.42 KY built a ground nest for herself and at 18.50 KK built one for
himself half a metre away from hers. The next morning both individuals were still in
their ground nests at 06.30 but left shortly afterwards.
In an effort to get at the significance of nests for chimpanzees, Croxall (2002) studied
nests of the Sonso chimpanzees in relation to their habitat, range and social groupings.
She noted that chimpanzee nests are not concerned with giving birth or rearing offspring
as they are in many species and do not represent ‘homes’ in any sense. However, they
are places of security, fixed points in the landscape of their range, and, even if tem-
porary, do represent markers of some kind within the territory.
We saw from Fig. 5.4 that party size declines at the end of the day as chimpanzees
approach nesting time. From 6.30 p.m. as dusk falls they form parties that will nest
together. We looked at night nesting party size and composition over a 14-month period
(Brownlow et al. 2001); 147 night nest parties were sampled between 19 October 1995
and 6 December 1996. Mean night nest party size (including dependent offspring)
was 4.5, with a range from 1 to 17. Party composition was analysed for the 147 night
nest parties using a principal components analysis. Mother–offspring pairs was the com-
monest combination; another common one consisted of the alpha and beta male dyad
(Duane and Vernon) and another was a disabled male with a juvenile male. Otherwise
individuals nested with others who happened to be nearby at the end of the day, though
there was a tendency for adult males to nest near (and lower than) adult females in
oestrus, perhaps ‘mate-guarding’ them or at least putting themselves in line for an early
pre-breakfast copulation, or even a nocturnal one (Singh 1999). One or more oestrous
females was present in 34 of the night nest parties studied. The size of those 34 parties
in which one or more oestrous females was present was compared with 20 parties in
which non-oestrous females without infants were present. The presence of oestrous
females had a significant effect, increasing the size of night nest parties, particularly the
number of adult males in the nest party.
98 Social organization