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

Interestingly, it is not just the presence of more males that increases party size when
oestrous females are present. There is also an increase in the percentage of females
joining the party (after excluding the oestrous females themselves). Thus, presence of
oestrous females is associated with larger party size generally. The maximum party size
seen with one or more oestrous females present was 28 (mean 10.22), whereas the max-
imum party size seen with no oestrous female present was 22 (mean 5.88). Thus mean
party size almost doubled when one or more oestrous females was present.

Seasonality 93

Fig. 5.4: Mean party size by time of day (courtesy of A. Plumptre, WCS, unpublished).

6

5

4

3

2

Number of individuals

1

0

7 8 9 10 11

Mean chimpanzee party size

12

Time

13 14 15 16 17 18 19

Time of day and party size

Mean party size was compared by time of day over a 15-month period using scan-based
party size data (Fig. 5.4). As can be seen, party size increases from 6.30 a.m. until
around 8 a.m., then levels off, dipping a little from mid-day until 2 p.m., then rises again
until 4.30 p.m. after which it drops decisively until nest-making time at 7 p.m.

Seasonality

Temperature and rainfall records are collected every day at Sonso camp. Temperature at
Budongo is fairly constant during the year, but rainfall varies with one major dry season,
as was seen in Fig. 1.2.
For purposes of seasonality analysis, the major dry season (January–February) was
compared with the remaining months (March–December). Tests were performed on