In the case of drumming, are individuals (males mainly but also a few females)
identifying themselves when they drum on the buttresses of trees, using their hands or
feet to produce a characteristic series of ‘boom-boom-booms’? The drumming patterns
of individual chimpanzees are in some cases distinct and can be distinguished by human
beings, so evidently individual chimpanzees have their trademark drumming patterns.
Besides our adult males we have two adult females at Sonso who occasionally accom-
pany their roar pant-hoots with drumming, each in her own distinctive way: Mukwano
and Kewaya. At Gombe, the adult females Fifi, Gremlin and Patti all do likewise, giving
roar pant-hoots accompanied by drumming occasionally, but never as often as males
(B. Wallauer, pers. comm.).
Barks
A recent study of chimpanzee vocalizations focuses not on pant-hoots but on barks.
Crockford and Boesch (2003) used discriminant function analysis to see whether the
barks (alarm calls) of chimpanzees at Taï were context specific in the way that, for exam-
ple, the alarm calls of vervet monkeys at Amboseli have been shown to be (Seyfarth
et al.1980). They found some evidence that they were. Their analysis was able to
distinguish two acoustically graded bark subtypes in the context of (a) hunting and
(b) presence of snakes. Second, they found some evidence for context-specific combina-
tions of barks with other call types or drumming. Chimpanzees produced context-specific
calls not only in the alarm context but also when travelling and hunting; the authors spec-
ulate that these may convey specific contextual information to listeners, but more study
is needed to confirm this by analysing the responses of listeners. This work and the
method used may mark a beginning of unravelling the semantics or ‘meanings’ of chim-
panzee calls. However, even if barks contain specific semantic messages that would not
imply that the same is true of pant-hoots, which could be functioning in a different way.
Screams
Studies of vocalizations are continuing at Budongo (Slocombe and Zuberbühler, 2005).
This study focuses on a hitherto neglected but common type of call given in agonistic
contexts: the scream. In this study, 14 different individuals contributed scream bouts to
the data, as both victims and aggressors; in addition 19 other individuals contributed
scream bouts but only in the role of victims. Most scream bouts consisted of three or
more screams, but the first three screams formed the basis of the analysis. Victim
screams were given by chimpanzees of all ages, ranks and sex. In contrast, aggressor
screams were mainly given by low ranking males, females or juveniles, whereas high
ranking males were typically silent when engaging in aggressive acts.
Slocombe and Zuberbühler found regular differences between victim screams and
aggressor screams in terms of the acoustic structure of the calls. Victim screams were
flatter and more symmetrically curved whereas aggressor screams were characterized
by a distinctive down-sweep after mid-call. The difference is shown in Fig. 6.10.
142 Social behaviour and relationships