The results of this study were that significant inter-population differences were found
to exist in the rate of delivery and fundamental frequency of the calls, with Budongo
chimpanzees having a faster build-up phase and a lower fundamental frequency (lower
‘pitch’) in both build-up and climax phases than Kibale chimpanzees. Bringing in
Wong’s comparisons also, she found that Budongo chimpanzees had a slower rate of
delivery of the build-up phase than Gombe chimps. That puts the Budongo chimpanzees
between Kibale with the slowest build-up or even no build-up phase at all (Clark Arcadi
1996), and Gombe with the fastest build-up.
The fundamental frequency (pitch) of the build-up phase in Budongo was found by
Notman to be significantly lower than that at Kibale. Wong did not find a significant
difference between Budongo and Gombe. Mitani et al. (1999) found that males at
Mahale had a higher pitched climax than Gombe chimpanzees. Thus these four-way
comparisons are not able to be put into a linear sequence as with the build-up phase
(above) but we don’t have a proper comparison between Budongo and Mahale. It may
be therefore that the Budongo chimpanzees are at the low end for pitch in their pant-
hoots, with Gombe and Kibale in the middle, and Mahale at the high end. This remains
to be ascertained.
Since the work of Notman and Wong (above), Marshall et al. (1999) in a study of the
vocalizations of captive chimpanzees in two facilities in the USA found that there were
differences between them. Although the individuals in each place had come from a vari-
ety of sources, their vocalizations in each shared common features which must have
been learned. In addition, a novel pant-hoot variant introduced by one male to one of the
groups spread to five other males in the same group suggesting that males modify their
calls through learning.
One thing is clear from the acoustic analyses we have looked at: the variations found
do not follow a geographical pattern. It is not the case, for example, that as you move
from south to north the variation changes in a regular way. Budongo is not between
Kibale and Gombe geographically. In this respect the variations in pant-hoots are like
some other variations found, e.g. in hand-clasp grooming (see Whiten et al. 1999). The
variations found so far are probably not ecological in origin. The evidence indicates
that they are learned differences, cultural in origin, and transmitted by learning from
generation to generation. And, if pant-hoot structure changes according to the calls of
the alpha male, it must change quite often, for changes in leadership mostly occur at
a frequency of less than 10 years, so that the process of learning is a constant one.
Notman (2003) made a second, more detailed study of pant-hoots in the Sonso
community. He explored whether pant-hoots were a single type of call with a great deal of
variation, or whether distinct kinds of pant-hoots could be distinguished, and he looked for
referential aspects (meanings) of different variations of pant-hoots. He discovered four
different kinds of pant-hoots (although there were gradations between them) as follows:
- Roar pant-hoots. These were most likely to elicit a response and were primarily
given during travel on the ground. They may be concerned with locating and joining
other parties.
Pant-hoots 139