Chimpanzees of the Budongo Forest : Ecology, Behaviour, and Conservation

Nesting and nesting parties 97

Table 5.6: Day and night nests compared (both sexes, N104 day nests,

601 night nests).

Day nests Night nests Significance

(Mann–WhitneyU)

Nest height

Mean 15.4 m 12.1 m p0.0001

Tree DBH

Mean 43.0 cm 26.4 cm p0.0001

% Re-used 16.3% 9.6% p0.04

% Weak 60.0% 0.7% p0.0001

(^37) Nishida (pers. comm.) writes ‘At Mahale, in my impression, day beds are built lower than night beds.
I do not know why this is different between sites.’
in the tree. In regard to the relationship between males and females, nesting close
together, with the male lower than the female, may indicate a degree of sexual interest
between the two, as evidenced by a number of occasions on which males have shaken
branches at females in oestrus in whom they were interested, and later nested below
them, nesting either before or after the female.
We explored whether presence of an oestrous female in the party had any effect on the
height at which males nested; it did not.
The structure of day nests was compared with that of night nests. Day nests were
structurally simpler than night nests, more quickly made and less dense and leafy. As a
result they were less permanent and fell to pieces more rapidly than night nests. We con-
cluded that day and night nests need to be more clearly distinguished than is often the
case. They serve different functions: day nests for resting over short periods, night nests
for sleeping over periods of 10 –12 h. There was no sex difference in nest height for day
nests, they were higher than night nests^37 and were made in larger trees. Both day and
night nests were occasionally re-used (see Table 5.6).
The most commonly used tree for day and night nests was the ironwood tree,
Cynometra alexandri. This is a species characterized by many small leaves creating a
mass of foliage and doubtless making comfortable nests. A different species,Uvariopsis
congensis, was favoured in a study of 143 nests in the northeast of Budongo forest, at
Kaniyo-Pabidi (O’Hara and O’Hara 2001), with 74% of all nests being made in that
species.Uvariopsislike Cynometrahas many small leaves but is lower than Cynometra,
being an understorey tree that often grows beneath Cynometrain Kaniyo-Pabidi
(S. O’Hara, pers. comm.). Mean night nesting height was just below 12 m at Kaniyo-
Pabidi, just above 12 m at Sonso (see Table 5.6).
Nest structure and nest types were distinguished by McVittie (1998). He climbed
up to 65 nests and was able to distinguish six types. Monostatic nests, mostly made
by males, were low (5–10 m) and made from a single small tree stem, often bowed
over by the weight of the chimpanzee, while female monostatic nests were higher
(15–20 m) and situated at the terminal tips of crown branches in smaller, unbent